Advanced Programming (C++)

Ahmad Yoosofan

University of Kashan

http://yoosofan.github.io/course/cpp.html

Files

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• Binary Files

---

 1 #include<fstream>
 2 #include<iostream>
 3 using namespace std;
 4 int main(){
 5   int i;
 6   ofstream f1("2.out.txt");
 7   for(i = 0; i < 20; i++)
 8     f1 << i << endl;
 9   f1 << "salam" << endl;
10   f1.close();
11 }

---

 1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 int main(){
 5   ifstream f1("input.integers.txt");
 6   if(!f1){
 7     cout << "The file could not be opened " << endl;
 8     throw 1;
 9   }
10   int i; //cin>>i;
11   f1 >> i;
12   cout << i << endl;
13   f1 >> i;
14   cout << i << endl;
15   f1.close();
16 }

---

 1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 int main(){
 5   ofstream f1("2.out.txt");
 6   if(!f1){
 7     cout << "The file could not be opened " << endl;
 8     throw 1;
 9   }
10   int i = 819; //cin>>i;
11   f1 << i << "  ";
12   cout << i << endl;
13   i = 4765;
14   f1 << i;
15   cout << i << endl;
16   f1.close();
17 }

---

 1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 int main(){
 5   ifstream f1("input.integers.txt");
 6   //ifstream f1("folder2/folder3/file1.txt");
 7   //ifstream f1("../../folder2/folder3/file1.txt");
 8 /*
 9   Relative addressing:
10   آدرس دهی نسبی در این جا یعنی از پوشه‌ی کنونی یکی بالاتر برو
11   سپس در آن پوشه به داخل پوشه‌ی folder2 برو سپس از آنجا به پوشه‌ی folder3 برو
12   در آن پوشه‌ی آخری پرونده‌ای به نام file1.txt باید وجود داشته باشد
13   ../folder2/folder3/file1.txt
14  Absolute addressing
15  آدرس دهی مطلق، مسیر را کامل از / مشخص می‌کند و دقیق مسیر مشخص می‌شود.
16  /home/ahmad/folder2/file1.txt
17  یا در ویندوز به صورت
18  D:\\folder2\\file1.txt
19  توضیح بیشتر درباره‌ی آن را در کلاس بپرسید تا توضیح دهم
20 */
21   if(!f1){
22     cout<<"The file could not be opened "<<endl;
23     throw 1;
24   }
25   int i; //cin>>i;
26   f1 >> i;
27   cout << i << endl;
28   f1 >> i;
29   cout << i << endl;
30   f1.close();
31 }

---

 1 #include<fstream>
 2 #include<iostream>
 3 #include<iomanip>
 4 using namespace std;
 5 const int MAX_STR = 200;
 6 int main(){
 7   char st[MAX_STR];
 8   string st2;
 9   ifstream f1("input.students.txt");
10   if(!f1){
11     cout << "couldn't open" << endl;
12     throw "Cannot open file";
13   }
14   f1.read(st, MAX_STR - 1); // 199 charactes + \0
15   while(!f1.eof()){
16   //~ while(getline(f1, st2)){
17     //~ st[9]= 0;
18     cout << st << endl;
19     //~ cout << st2 << endl;
20     //~ f1.seekg(9, ios::cur);
21     f1.read(st, MAX_STR - 1);
22   }
23   cout << st << endl;
24   f1.close();
25   cout << std::hex << int('9') << endl;
26   //~ cout << std::hex << int('7') << endl;
27   //~ cout << std::hex << int('4') << endl;
28   //~ cout << std::hex << int('3') << endl;
29 }

---

 1 #include<fstream>
 2 #include<iostream>
 3 using namespace std;
 4 const int MAX_STR = 200;
 5 int main(){
 6   char st[MAX_STR];
 7   ifstream f1;
 8   f1.open("input.students.txt");
 9   if(!f1)
10     cout << "couldn't open" << endl;
11   else {
12     f1.getline(st, MAX_STR - 1);
13     while(! f1.eof()){
14       cout << st << endl;
15       f1.getline(st, MAX_STR - 1);
16     }
17     f1.close();
18   }
19 }
20 /* Rererence for more study
21  * http://www.cplusplus.com/reference/fstream/fstream/open/
22 */

---

 1 #include<fstream>
 2 #include<iostream>
 3 using namespace std;
 4 const int MAX_STR = 200;
 5 int main(){
 6   char st[MAX_STR];
 7   ifstream f1;
 8   f1.open("input.students.txt");
 9   if(!f1.is_open() )
10     cout << "couldn't open" << endl;
11   else {
12     f1.getline(st, MAX_STR - 1);
13     while(! f1.eof()){
14       cout << st << endl;
15       f1.getline(st, MAX_STR - 1);
16     }
17     f1.close();
18   }
19   return 0;
20 }
21 /* Rererence for more study
22  * http://www.cplusplus.com/reference/fstream/fstream/is_open/
23 */

---

 1 #include<fstream>
 2 #include<iostream>
 3 using namespace std;
 4 const int MAX_STR = 200;
 5 int main(){
 6   char st[MAX_STR];
 7   ifstream f1("input.students.txt");
 8   if(! f1){
 9     cout << "couldn't open" << endl;
10     throw 1;
11   }
12   //cout<<f1.getline(st,200).gcount()<<endl;
13   while(f1.getline(st, MAX_STR - 1).gcount() > 0 )
14     cout << st << endl;
15   f1.close();
16 }

---

 1 #include <fstream>
 2 #include <iostream> //#include <cstdlib>
 3 using namespace std;
 4 int main(){
 5   string st= "ali";
 6   ofstream f1("2.out.txt");
 7   fstream f2("3.out.txt", ios::out); //ofstream
 8   if(!f1){
 9     cout << "Can not open f1" << endl;
10     throw 1;
11   }
12   if(!f2){
13     cout << "Can not open f2" << endl;
14     f1.close();
15     throw 2;
16   }
17   f1 << st << ' ' << "Hamed" << endl;
18   f2 << "Sadegh" << "  Salehi " << endl;
19   f2.close();
20   f1.close();
21   fstream f3("2.out.txt", ios::in);
22   if(!f3){
23     cout << "Can not open f3" << endl;
24     throw 0;
25   }
26   f3 >> st;
27   cout << st << endl;
28   f3.close();
29   ifstream f4("3.out.txt");
30   char cst[50];
31   f4.getline(cst,50);
32   cout << cst << endl;
33   f4.close();
34 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 using namespace std;
 4 int main(){
 5   string st =  "ali";
 6   ofstream f1("2.out.txt");
 7   fstream f2("3.out.txt", ios::out); //ofstream
 8   if(!f1)
 9     cout << "Can not open f1" << endl;
10   if(!f2)
11     cout << "Can not open f2" << endl;
12   f1 << st << endl << "Hamed" << endl;
13   f2 << "Sadegh" << "  Salehi " << endl;
14   f2 << "ali" << "  Seifi " << endl;
15   f2 << "Sahar" << "  Safi " << endl;
16   f2.close();
17   f1.close();
18   fstream f3("2.out.txt",ios::in);
19   if(!f3){
20     cout << "Can not open f3" << endl;
21     return 0;
22   }
23   f3 >> st;
24   cout << st << endl;
25   f3.close();
26   ifstream f4("3.out.txt");  //f4>>st; cout<<st<<endl;
27   char cst[50];  //while(f4.getline(cst,50).gcount()>0)
28   while(f4.getline(cst, 50))
29     cout<< cst << endl;
30   f4.close();
31 }

---

 1 #include<fstream>
 2 #include<iostream>
 3 using namespace std;
 4 struct student{
 5   int std_no;
 6   char name[100];
 7   double avg;
 8   char course[100];
 9   int m, n;
10   void readFromFile(ifstream& f1){
11     f1 >> std_no;
12     f1 >> name;
13     f1 >> avg;
14     f1 >> course;
15     f1 >> m;
16     f1 >> n;
17   }
18   void print(void){
19     cout << std_no <<'\t';
20     cout << name << '\t';
21     cout << avg << '\t';
22     cout << course << '\t';
23     cout << m << '\t';
24     cout << n << endl;
25   }
26 };
27 int main(){
28   int i;
29   double x;
30   char st[100];
31   student m1;
32   ifstream f1("input.students.txt"); // ofstream , ifstream, fstream
33   m1.readFromFile(f1);
34   while(!f1.eof()){
35     m1.print();
36     m1.readFromFile(f1);
37   }
38   //while(f1>>i) cout<<i<<'\t';cout<<endl;
39   //f1.close();  f1.open("1.inp.txt");
40   //f1.seekg(0,ios::beg);
41   //while(!f1.eof()){ cout<<i<<'\t';f1>>i;} cout<<endl;
42   f1.close();
43 }
44 /*
45   void read2(ifstream&f1){
46   constexpr auto max_string=1000;
47   constexpr auto max_stringMinus1=1000-1;
48   char st[max_string];
49   f1.getline(st,max_stringMinus1);
50   sscanf(st,"%d%s%lf%s%d%d",&std_no,name, &avg, course, &m, &n);
51   }
52 */

---

 1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 class myIntArray{
 5   static const int N = 2000;
 6   int a[N];
 7   ifstream f1;
 8   int n;
 9   public:
10   myIntArray(const char* fileName = "input.integers.txt"){
11     int i;
12     f1.open(fileName);
13     if(!f1){
14       cout << "file ";
15       throw "cannot open file"; // throw
16     }
17     for(i = 0 ; f1 >> a[i] && i < N; i++)
18       ;
19     n = i;
20     f1.close();
21   }
22   void sort(void){
23     int i, j;
24     for(i = 0; i < n-1; i++)
25       for(j = i+1; j < n; j++)
26         if(a[i] > a[j]){
27           int temp = a[i];
28           a[i] = a[j];
29           a[j]=temp;
30         }
31   }
32   int search(int key){
33     for(auto i = 0; i < n; i++)
34       if(a[i] == key)
35         return i;
36     return -1;
37   }
38   void print(void){
39     for(auto i = 0; i < n; i++)
40       cout << a[i] << endl;
41     }
42 };
43 int main(){
44   myIntArray m1("input.integers.txt");
45   m1.sort();
46   cout << m1.search(12) << endl;
47   m1.print();
48 }

---

 1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 class myIntArray{
 5   const static int N = 2000;
 6   int a[N];
 7   ifstream f1;
 8   int n;
 9  public:
10   myIntArray(const char* fileName = "input.integers.txt"){
11     int i;
12     f1.open(fileName);
13     if(!f1){
14       cout<<"file ";
15       throw "cannot open file";
16     }
17     for(i=0; f1 >> a[i] && i<N; i++)
18       ;
19     n = i;
20     f1.close();
21   }
22   void sort(void){
23     int i,j, temp;
24     for(i=0;i<n-1;i++)
25       for(j=i+1;j<n;j++)
26         if(a[i]>a[j]){
27           temp = a[i];
28           a[i] = a[j];
29           a[j] = temp;
30         }
31   }
32   int search(int key){
33     for(int i=0; i < n; i++)
34       if(a[i] == key)
35         return i;
36     return -1;
37   }
38   void print(void){
39     for(int i=0; i<n; i++)
40       cout << a[i] << endl;
41   }
42 };
43 int main(){
44   myIntArray m1("input.integers.txt");
45   m1.sort();
46   cout << m1.search(12) << endl;
47   m1.print();
48   return 0;
49 }

---

 1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 class myIntArray{
 5   int* a;
 6   fstream f1;
 7   int n;
 8   public:
 9   myIntArray(const char* fileName="input.integers.txt"){
10     int i;
11     f1.open(fileName);
12     if(!f1){
13       cout << "file ";
14       throw "cannot open file";
15     }
16     a = new int[2000];
17     int k = 2000;
18     for(i=0; f1 >> a[i]; i++)
19       if(i > k-2){
20         int* b = new int[k *= 2];
21         for(int j=0; j < i; j++)
22           b[j] = a[j];
23         delete[] a;
24         a = b;
25       }
26     n = i;
27     f1.close();
28   }
29   ~myIntArray(){delete[] a;}
30   void sort(void){
31     int i, j, temp;
32     for(i=0; i<n-1; i++)
33       for(j=i+1; j<n; j++)
34         if(a[i] > a[j]){
35           temp = a[i];
36           a[i] = a[j];
37           a[j] = temp;
38         }
39   }
40   int search(int key){
41     for(int i=0; i < n; i++)
42       if(a[i] == key)
43         return i;
44     return -1;
45   }
46   void print(void){
47     for(int i=0; i<n; i++)
48       cout << a[i] << endl;
49   }
50 };
51 int main(){
52   myIntArray m1("input.integers.txt");
53   m1.sort();
54   cout << m1.search(12) << endl;
55   m1.print();
56   return 0;
57 }

---

 1 // https://www.systutorials.com/how-to-process-a-file-line-by-line-in-c/
 2 #include <iostream>
 3 #include <fstream>
 4 #include <string>
 5 int main (){
 6   std::ifstream file("input.txt");
 7   std::string str;
 8   while (std::getline(file, str))
 9     std::cout << str << "\n";
10 }

---

 1 // https://codereview.stackexchange.com/a/38954
 2 // https://codereview.stackexchange.com/questions/38879/parsing-text-file-in-c
 3 // https://www.codespeedy.com/cpp-program-to-create-a-text-file-open-and-read-a-particular-line/
 4 // http://www.cplusplus.com/forum/beginner/11304/
 5 // https://www.tutorialspoint.com/read-file-line-by-line-using-cplusplus
 6 // https://www.geeksforgeeks.org/encrypt-and-decrypt-text-file-using-cpp/
 7 // https://coderedirect.com/questions/119182/how-to-read-a-file-line-by-line-or-a-whole-text-file-at-once
 8 // https://www.codegrepper.com/code-examples/cpp/getline+from+file+c%2B%2B
 9 // https://www.educba.com/c-plus-plus-getline/
10 // https://www.codegrepper.com/code-examples/cpp/getline+from+file+c%2B%2B
11 // https://stackoverflow.com/questions/43573658/c-how-to-read-a-line-of-text-from-file-to-char-array
12 // https://www.geeksforgeeks.org/getline-string-c/
13 
14 struct Person
15 {
16     std::string name;
17     std::string age;
18     std::string salary;
19     std::string hoursWorked;
20     std::string randomText;
21 
22     friend std::istream& operator>>(std::istream& str, Person& data)
23     {
24         std::string line;
25         Person tmp;
26         if (std::getline(str,line))
27         {
28             std::stringstream iss(line);
29             if ( std::getline(iss, tmp.name, ':')        &&
30                  std::getline(iss, tmp.age, '-')         &&
31                  std::getline(iss, tmp.salary, ',')      &&
32                  std::getline(iss, tmp.hoursWorked, '[') &&
33                  std::getline(iss, tmp.randomText, ']'))
34              {
35                  /* OK: All read operations worked */
36                  data.swap(tmp);  // C++03 as this answer was written a long time ago.
37              }
38              else
39              {
40                  // One operation failed.
41                  // So set the state on the main stream
42                  // to indicate failure.
43                  str.setstate(std::ios::failbit);
44              }
45         }
46         return str;
47     }
48     void swap(Person& other) throws() // C++03 as this answer was written a long time ago.
49     {
50         swap(name,        other.name);
51         swap(age,         other.age);
52         swap(salary,      other.salary);
53         swap(hoursWorked, other.hoursWorked);
54         swap(randomText,  other.randomText)
55     }
56 };

Bianry file

 1 #include <fstream>
 2 #include<iostream>
 3 using namespace std;
 4 int main(){
 5   int i = 12;
 6   ofstream f1("a1.txt", ios::binary);
 7   if(!f1)
 8     throw "Cannot Open File";
 9   f1.write((char*) &i, sizeof(int));
10   const char* st1="ABC";
11   const char st2[]{'A', 'B', 'C', '\0'};
12   const char st3[]{65, 66, 67, 0};
13   const char st4[]{0x41, 0x42, 0x43, 0x0};
14   f1.write((char*) st1, 4 * sizeof(char));
15   f1.write((char*) st2, 4 * sizeof(char));
16   f1.write((char*) st3, 4 * sizeof(char));
17   f1.write((char*) st4, 4 * sizeof(char));
18   f1.write((char*) &(++i), sizeof(int));
19   // f1.write((char *) &(i++),sizeof(int));
20   // f1.write((char *) &(i+1),sizeof(int));
21   f1.write((char*) &(++i), sizeof(int));
22   f1.write((char*) &(i += 234234), sizeof(int));
23   f1.close();
24 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 using namespace std;
 4 int main(){
 5   int i = 12, j;
 6   ofstream f1("a1.txt", ios::binary);
 7   if(!f1)
 8     throw "Cannot Open File";
 9   f1.write((char*) &i, sizeof(int));
10   const char* st1="ABC";
11   const char st2[]{'A', 'B', 'C', '\0'};
12   const char st3[]{65, 66, 67, 0};
13   const char st4[]{0x41, 0x42, 0x43, 0x0};
14   f1.write((char*) st1, 4 * sizeof(char));
15   f1.write((char*) st2, 4 * sizeof(char));
16   f1.write((char*) st3, 4 * sizeof(char));
17   f1.write((char*) st4, 4 * sizeof(char));
18   f1.write((char*) &(++i), sizeof(int));
19   // f1.write((char *) &(i++),sizeof(int));
20   // f1.write((char *) &(i+1),sizeof(int));
21   f1.write((char*) &(++i), sizeof(int));
22   f1.write((char*) &(i += 234234), sizeof(int));
23   f1.close();
24   fstream f3("a1.txt", ios::in | ios::binary);
25   if(!f3)
26       throw "Cannot Open File";
27   f3.read((char*) &j, sizeof(int));
28   char ast[20];
29   f3.read(ast, 4 * sizeof(char));
30   f3.read(ast+4, 4 * sizeof(char));
31   f3.read(ast+8, 4 * sizeof(char));
32   f3.read(ast+12, 4 * sizeof(char));
33   cout << j << endl;
34   cout << ast << endl;
35   cout << ast + 4 << endl;
36   cout << ast + 8 << endl;
37   cout << ast + 12 << endl;
38   cout << "number of read character: "
39     << f3.read((char*) &j, sizeof(int)).gcount() << endl;
40   while(f3.read((char*) &j, sizeof(int)))
41       cout << j << endl;
42   f3.close();
43 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 using namespace std;
 4 void write2file(const char* fname);
 5 void readFromFile(const char* fname);
 6 int main(){
 7   write2file("a1.bin");
 8   readFromFile("a1.bin");
 9 }
10 void write2file(const char* fname = "a1.bin"){
11   ofstream f1(fname, ios::binary);
12   // fstream f1(fname, ios::out | ios::binary);
13   if(!f1) throw "Cannot Open File";
14   int i = 6, j = 1;
15   f1.write((char*) &i, sizeof(int));
16   for(; i > 0; i--)
17     f1.write((char*) &(j += 3), sizeof(int));
18   f1.close();
19 }
20 void readFromFile(const char* fname = "a1.bin"){
21     //fstream f3(fname, ios::in | ios::binary);
22     ifstream f3(fname, ios::binary);
23     if(!f3)   throw "Cannot Open File";
24     int n, j;
25     f3.read((char*) &n, sizeof(int));
26     for(; n > 0; n--){
27         f3.read((char*) &j, sizeof(int));
28         cout << j << endl;
29     }
30     f3.close();
31 }

---

 1 #include <fstream>
 2 #include <iostream>
 3 using namespace std;
 4 class myArray{
 5   fstream f1;
 6   public:
 7   myArray(const char* fname = "temp1.in"){
 8     f1.open(fname, ios::in | ios::out | ios::binary);
 9     if(!f1){
10       f1.open(fname, ios::out | ios::binary);
11       if(!f1){
12         cout << "Can not open file" << endl;
13         throw "Cannot Open File";
14       }else{
15         f1.close();
16         f1.open(fname, ios::in | ios::out | ios::binary);
17       }
18     }
19   }
20   ~myArray(){f1.close();}
21   int read(const int index){
22     int j;
23     f1.seekg(index * sizeof(int), ios::beg); // ios::end  ios::cur
24     f1.read((char*) &j, sizeof(int));
25     return j;
26   }
27   void write(int data, int index){
28       f1.seekp(index * sizeof(int), ios::beg);
29       f1.write((char*) &data, sizeof(int));
30   }
31   int readNext(void){
32     int j;
33     f1.read((char*) &j, sizeof(int));
34     return j;
35   }
36   void writeNext(int j)
37   {f1.write((char*) &j, sizeof(int));}
38   void rewind(void){
39     f1.seekg(0, ios::beg);
40     f1.seekp(0, ios::beg);
41   }
42 };
43 int main(){
44   myArray myi;
45   myi.writeNext(12);
46   myi.writeNext(14);
47   myi.rewind();
48   cout << myi.readNext() << endl;
49   cout << myi.readNext() << endl;
50   cout << myi.read(0) << endl;
51   cout << myi.read(1) << endl;
52   myi.write(13, 10);
53   cout<<myi.read(25)<<endl<<endl;
54 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 using namespace std;
 5 template<typename T>class myArray{
 6   fstream f1;
 7   public:
 8   myArray(const char* fname = "temp1.in"){
 9     f1.open(fname, ios::in | ios::out | ios::binary);
10     if(!f1){
11       f1.open(fname, ios::out | ios::binary);
12       if(!f1){
13         cout << "Can not open file" << endl;
14         exit(0);
15       }else{
16         f1.close();
17         f1.open(fname, ios::in |ios::out |ios::binary);
18       }
19      }
20   }
21   ~myArray(){ f1.close();}
22   T read(int index){ T j;
23     f1.seekg(index * sizeof(T), ios::beg);
24     f1.read((char*) &j, sizeof(T));
25     return j;
26   }
27   void write(const T j, const int index){
28     f1.seekp(index * sizeof(T), ios::beg);
29     f1.write((char*) &j , sizeof(T));
30   }
31   T readNext(void){ T j;
32     f1.read((char*) &j , sizeof(T));
33     return j;
34   }
35   void writeNext(T j){f1.write((char*) &j, sizeof(T));}
36   void rewind(void){
37     f1.seekg(0, ios::beg);
38     f1.seekp(0, ios::beg);
39   }
40  };
41 int main(){
42   myArray<int> myi("temp4.in");
43   myi.writeNext(16);  myi.writeNext(19);  myi.rewind();
44   cout << myi.readNext() << endl;
45   cout << myi.readNext() << endl;
46   cout << myi.read(0) << endl;
47   cout << myi.read(1) << endl;
48   myArray<double> my2; my2.writeNext(4.23);
49   my2.writeNext(5.34); my2.writeNext(67.43); my2.rewind();
50   cout << my2.readNext() << endl << my2.readNext() << endl;
51 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T> class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const char* fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13       if(!f1){
14         cout << "Can not open file" << endl;
15         throw "Cannot Open File";
16       }else{
17         f1.close();
18         f1.open(fname, ios::in | ios::out | ios::binary);
19       }
20     }
21   }
22   ~myArray(){
23     f1.close();
24   }
25   T read(const int index){
26     T data;
27     f1.seekg(index * sizeof(T), ios::beg);
28     // ios::end   ios::cur
29     f1.read((char*) &data, sizeof(T));
30     return data;
31   }
32   void write(const T& data, const int index){
33     f1.seekp(index * sizeof(T), ios::beg);
34     f1.write((char*) &data, sizeof(T));
35   }
36   T readNext(void){
37     T data;
38     f1.read((char*) &data, sizeof(T));
39     return data;
40   }
41   void writeNext(T data){
42     f1.write((char*) &data, sizeof(T));
43   }
44   void rewind(void){
45     f1.seekg(0, ios::beg);
46     f1.seekp(0, ios::beg);
47   }
48 };
49 struct student{
50   char name[20];
51   char stdno[14];
52   double avg;
53   void print(void){
54     cout << "name:" << name << endl << "stdno:" << stdno
55       << endl << "avg:" << avg << endl;
56   }
57 };
58 int main(){
59   myArray<student> myi("temp6.in");
60   student st1{"Ali", "933424", 15.1};
61   myi.writeNext(st1);
62   strcpy(st1.name, "Reza");
63   strcpy(st1.stdno, "923434");
64   st1.avg = 14.2;
65   myi.writeNext(st1);
66   myi.rewind();
67   myi.readNext().print();
68   myi.readNext().print();
69   myi.read(0).print();
70   myi.read(1).print();
71   return 0;
72 }

---

 1 // Error
 2 #include <fstream>
 3 #include<iostream>
 4 #include <cstdlib>
 5 #include<cstring>
 6 using namespace std;
 7 template<typename T> class myArray{
 8   fstream f1;
 9   public:
10   myArray(const char* fname = "temp1.in"){
11     f1.open(fname, ios::in | ios::out | ios::binary);
12     if(!f1){
13       f1.open(fname, ios::out | ios::binary);
14       if(!f1){
15         cout << "Can not open file" << endl;
16         throw "Cannot Open File";
17       }else{
18         f1.close();
19         f1.open(fname, ios::in | ios::out | ios::binary);
20       }
21     }
22   }
23   ~myArray(){
24     f1.close();
25   }
26   T read(int index){
27     T data;
28     f1.seekg(index * sizeof(T), ios::beg); // ios::end   ios::cur
29     f1.read((char*) &data, sizeof(T));
30     return data;
31   }
32   void write(const T data, int index){
33     f1.seekp(index * sizeof(T), ios::beg);
34     f1.write((char*) &data, sizeof(T));
35   }
36   T readNext(void){
37     T data;
38     f1.read((char*) &data , sizeof(T));
39     return data;
40   }
41   void writeNext(T data){
42     f1.write((char*) &data, sizeof(T));
43   }
44   void rewind(void){
45     f1.seekg(0, ios::beg);
46     f1.seekp(0, ios::beg);
47   }
48  };
49 struct student{
50   char name[20];
51   char stdno[14];
52   double avg;
53   friend ostream & operator<<(ostream & o1, student m1){
54     o1 << "( " << m1.name << " , " << m1.stdno
55       << " , " << m1.avg << " ) ";
56     return o1;
57   }
58   char& operator[](int& index);
59 };
60 int mystrlen(char* s){
61   int i;
62   for(i = 0; s[i]; i++);
63   return i;
64 }
65 char& student::operator[](int& index){
66   if(index < mystrlen(stdno))
67     return stdno[index];
68   return stdno[0];
69 }
70 int main(){
71   myArray<student> myi("temp6.in");
72   student st1 {"Ali", "933424", 15.1};
73   cout << st1[1] << endl;
74   st1[1] = '2';
75   myi.writeNext(st1);
76   strcpy(st1.name, "Reza");
77   strcpy(st1.stdno, "923434");
78   st1.avg = 14.2;
79   myi.writeNext(st1);
80   myi.rewind();
81   cout << myi.readNext() << endl;
82   //operator<<(cout,myi.readNext());
83   //student *ps= & myi.readNext(); Error
84   cout << myi.readNext() << endl;
85   cout << myi.read(0) << endl;
86   cout << myi.read(1) << endl;
87   //myi.write(54,10);
88   //cout<<myi.read(25)<<endl<<endl;
89   return 0;
90 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T> class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const string fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13       if(!f1)
14         throw fname + "Can not open file" ;
15       else{
16         f1.close();
17         f1.open(fname, ios::in | ios::out | ios::binary);
18       }
19     }
20   }
21   ~myArray(){ f1.close();}
22   T read(int index){
23     T j;
24     f1.seekg(index * sizeof(T), ios::beg);
25     f1.read((char*) &j , sizeof(T));
26     return j;
27   }
28   void write(T j, int index){
29     f1.seekp(index * sizeof(T), ios::beg);
30     f1.write((char*) &j, sizeof(T));
31   }
32   T readNext(void){
33     T j;
34     f1.read((char*) &j, sizeof(T));
35     return j;
36   }
37   void writeNext(T j){
38     f1.write((char*) &j, sizeof(T));
39     f1.flush();
40   }
41   void rewind(void){
42     f1.seekg(0, ios::beg);
43     f1.seekp(0, ios::beg);}
44  };
45 struct student{
46   char name[20];
47   char stdno[14];
48   double avg;
49   friend ostream& operator<<(ostream & o1, student m1){
50     o1<<"( "<<m1.name<<" , "<<m1.stdno<<
51     " , "<<m1.avg<<" ) ";
52     return o1;
53   }
54   char& operator[](const int& index){
55     if(unsigned(index) < strlen(stdno))
56       return stdno[index];
57     return stdno[0];
58   }
59 };
60 int main(){
61   myArray<student> myi("temp6.in");
62   student st1 = {"Ali", "933424", 15.1};
63   int a = 1;
64   cout << st1[a] << endl;
65   st1[1] = '2';
66   myi.writeNext(st1);
67   strcpy(st1.name, "Reza");
68   strcpy(st1.stdno, "923434");
69   st1.avg = 14.2;
70   myi.writeNext(st1);
71   myi.rewind();
72   cout << myi.readNext() << endl;
73   cout << myi.readNext() << endl;
74   cout << myi.read(0) << endl;
75   cout << myi.read(1) << endl;
76   return 0;
77 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T>class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const char* fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13       if(!f1){
14         cout << "Can not open file" << endl;
15         exit(0);
16       }else{
17         f1.close();
18         f1.open(fname, ios::in | ios::out | ios::binary);
19       }
20     }
21   }
22   ~myArray(){ f1.close();}
23   T read(const int index){
24     T j;
25     f1.seekg(index * sizeof(T), ios::beg);
26     // ios::end   ios::cur
27     f1.read((char*) &j , sizeof(T));
28     return j;
29   }
30   void write(T j, int index){
31     f1.seekp(index * sizeof(T), ios::beg);
32     f1.write((char*) &j , sizeof(T));
33   }
34   T& readNext(void){
35     static T j;
36     f1.read((char*) &j ,
37     sizeof(T));
38     return j;
39   }
40   void writeNext(T j){
41     f1.write((char*) &j, sizeof(T));
42     f1.flush();
43   }
44   void rewind(void){
45     f1.seekg(0, ios::beg);
46     f1.seekp(0, ios::beg);
47   }
48  };
49 struct student{
50   char name[20];
51   char stdno[14];
52   double avg;
53   friend ostream& operator<<(ostream& o1, const student& m1){
54     o1 << "( " << m1.name << " , " << m1.stdno
55       << " , " << m1.avg << " ) ";
56     return o1;
57   }
58   char& operator[](const int& index);
59 };
60 inline char& student::operator[](const int& index){
61   if(unsigned(index) < strlen(stdno))
62     return stdno[index];
63   return stdno[0];
64 }
65 int main(){
66   myArray<student> myi("temp6.in");
67   //~ unsigned aa =1;
68   //~ unsigned int ddd = 33;
69   //~ unsigned char dddrr = 'c';
70   student st1 = {"Ali", "933424", 15.1};
71   int a = 1;
72   cout << st1[a] << endl;
73   st1[1] = '2';
74   myi.writeNext(st1);
75   strcpy(st1.name, "Reza");
76   strcpy(st1.stdno, "923434");
77   st1.avg=14.2;
78   myi.writeNext(st1);
79   myi.rewind();
80   cout << myi.readNext() << endl;
81   student* ps = &myi.readNext(); //Error
82   cout << *ps <<endl;
83   cout << myi.readNext() <<endl;
84   cout << myi.read(0) << endl;
85   cout << myi.read(1) << endl;
86   return 0;
87 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T> class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const char* fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13       if(!f1){
14         cout << "Can not open file" << endl;
15         exit(0);
16       }else{
17         f1.close();
18         f1.open(fname, ios::in | ios::out | ios::binary);
19       }
20     }
21   }
22   ~myArray(){ f1.close();}
23   T read(const int index){
24     T j;
25     f1.seekg(index * sizeof(T), ios::beg);
26     f1.read((char*) &j, sizeof(T));
27     return j;
28   }
29   void write(T j, int index){
30     f1.seekp(index * sizeof(T), ios::beg);
31     f1.write((char*) &j, sizeof(T));
32   }
33   T& readNext(void){
34     static T j;
35     f1.read((char*) &j, sizeof(T));
36     return j;
37   }
38   void writeNext(T j){
39     f1.write((char*) &j, sizeof(T));
40     f1.flush();
41   }
42   void rewind(void){
43     f1.seekg(0, ios::beg);
44     f1.seekp(0, ios::beg);
45   }
46  };
47  struct student{
48   char name[20];
49   char stdno[14];
50   double avg;
51   friend ostream& operator<<(ostream& o1, const student& m1){
52     o1 << "( " << m1.name << " , " << m1.stdno
53       << " , " << m1.avg << " ) ";
54     return o1;
55   }
56   char& operator[](const int& index){
57     if(unsigned(index) < strlen(stdno))
58       return stdno[index];
59     return stdno[0];
60   }
61 };
62 int main(){
63   myArray<student> myi("temp6.in");
64   student st1 = {"Ali", "933424", 15.1};
65   int a = 1;
66   cout << st1[a] << endl;
67   st1[1] = '2';
68   myi.writeNext(st1);
69   strcpy(st1.name, "Reza");
70   strcpy(st1.stdno, "923434");
71   st1.avg = 14.2;
72   myi.writeNext(st1);
73   myi.rewind();
74   cout << myi.readNext() << endl;
75   student* ps = &myi.readNext(); //Error
76   cout << *ps << endl;
77   cout << myi.readNext() << endl;
78   cout << myi.read(0) << endl;
79   cout << myi.read(1) << endl;
80   return 0;
81 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T> class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const string fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13       if(!f1)
14         throw fname + "Can not open file";
15       else{
16         f1.close();
17         f1.open(fname, ios::in | ios::out | ios::binary);
18       }
19     }
20   }
21   ~myArray(){ f1.close();}
22   T read(int index){
23     T j;
24     f1.seekg(index * sizeof(T), ios::beg);
25     f1.read((char*) &j , sizeof(T));
26     return j;
27   }
28   void write(T j, int index){
29     f1.seekp(index * sizeof(T), ios::beg);
30     f1.write((char*) &j, sizeof(T));
31   }
32   T readNext(void){
33     T j;
34     f1.read((char*) &j, sizeof(T));
35     return j;
36   }
37   void writeNext(T j){
38     f1.write((char*) &j, sizeof(T));
39     f1.flush();
40   }
41   void rewind(void){
42     f1.seekg(0, ios::beg);
43     f1.seekp(0, ios::beg);
44   }
45  };
46 struct student{
47   char name[20];
48   char stdno[14];
49   double avg;
50   friend ostream& operator<<(ostream & o1, student m1){
51     o1<<"( "<<m1.name<<" , "<<m1.stdno<<
52     " , "<<m1.avg<<" ) ";
53     return o1;
54   }
55   char& operator[](const int& index){
56     if(unsigned(index) < strlen(stdno))
57       return stdno[index];
58     return stdno[0];
59   }
60 };
61 int main(){
62   myArray<student> myi("temp6.in");
63   student st1 = {"Ali", "933424", 15.1};
64   int a = 1;
65   cout << st1[a] << endl;
66   st1[a] = '2';
67   myi.writeNext(st1);
68   strcpy(st1.name, "Reza");
69   strcpy(st1.stdno, "923434");
70   st1.avg = 14.2;
71   myi.writeNext(st1);
72   myi.rewind();
73   cout << myi.readNext() << endl;
74   cout << myi.readNext() << endl;
75   cout << myi.read(0) << endl;
76   cout << myi.read(1) << endl;
77   return 0;
78 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T> class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const string fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13        if(!f1)
14          throw fname + "Can not open file";
15         else{
16           f1.close();
17           f1.open(fname, ios::in | ios::out | ios::binary);
18         }
19      }
20    }
21    ~myArray(){ f1.close();}
22    T read(int index){
23      T j;
24      f1.seekg(index * sizeof(T), ios::beg);
25      f1.read((char*) &j, sizeof(T));
26      return j;
27    }
28    void write(T j, int index){
29      f1.seekp(index * sizeof(T), ios::beg);
30      f1.write((char*) &j, sizeof(T));
31    }
32    T readNext(void){
33      T j;
34      f1.read((char *) &j, sizeof(T));
35      return j;
36    }
37    void writeNext(T j){
38      f1.write((char *) &j, sizeof(T));
39      f1.flush();
40    }
41    void rewind(void){
42      f1.seekg(0, ios::beg);
43      f1.seekp(0, ios::beg);
44     }
45  };
46 struct student{
47   char name[20];
48   char stdno[14];
49   double avg;
50   friend ostream& operator<<(ostream & o1, student m1){
51     o1<<"( "<<m1.name<<" , "<<m1.stdno<<
52     " , "<<m1.avg<<" ) ";
53     return o1;
54   }
55   char& operator[](int  index){
56     if(unsigned(index) < strlen(stdno))
57       return stdno[index];
58     return stdno[0];
59   }
60 };
61 int main(){
62   myArray<student> myi("temp6.in");
63   student st1 = {"Ali", "933424", 15.1};
64   int a = 1;
65   cout << st1[a] << endl;
66   st1[1] = '2';
67   myi.writeNext(st1);
68   strcpy(st1.name, "Reza");
69   strcpy(st1.stdno, "923434");
70   st1.avg = 14.2;
71   myi.writeNext(st1);
72   myi.rewind();
73   cout << myi.readNext() << endl;
74   cout << myi.readNext() << endl;
75   cout << myi.read(0) << endl;
76   cout << myi.read(1) << endl;
77   return 0;
78 }

---

 1 // Error
 2 #include <fstream>
 3 #include<iostream>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T> class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const string fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13       if(!f1)
14         throw fname + "Can not open file";
15       else{
16         f1.close();
17         f1.open(fname, ios::in | ios::out | ios::binary);
18       }
19     }
20   }
21   ~myArray(){ f1.close();}
22   T read(int index){
23     T j;
24     f1.seekg(index * sizeof(T), ios::beg);
25     f1.read((char*) &j, sizeof(T));
26     return j;
27   }
28   void write(T j, int index){
29     f1.seekp(index * sizeof(T), ios::beg);
30     f1.write((char*) &j, sizeof(T));
31   }
32   T readNext(void){
33     T j;
34     f1.read((char*) &j, sizeof(T));
35     return j;
36   }
37   void writeNext(T j){
38     f1.write((char*) &j, sizeof(T));
39     f1.flush();
40   }
41   void rewind(void){
42     f1.seekg(0, ios::beg);
43     f1.seekp(0, ios::beg);
44   }
45  };
46 struct student{
47   char name[20];
48   char stdno[14];
49   double avg;
50   friend ostream& operator<<(ostream& o1, student m1){
51     o1<<"( "<<m1.name<<" , "<<m1.stdno<<
52     " , "<<m1.avg<<" ) ";
53     return o1;
54   }
55   char operator[](int  index){
56     if(unsigned(index) < strlen(stdno))
57       return stdno[index];
58     return stdno[0];
59   }
60 };
61 int main(){
62   myArray<student> myi("temp6.in");
63   student st1 = {"Ali", "933424", 15.1};
64   int a = 1;
65   cout << st1[a] << endl;
66   myi.writeNext(st1);
67   strcpy(st1.name, "Reza");
68   strcpy(st1.stdno, "923434");
69   st1.avg = 14.2;
70   myi.writeNext(st1);
71   myi.rewind();
72   cout << myi.readNext() << endl;
73   cout << myi.readNext() << endl;
74   cout << myi.read(0) << endl;
75   cout << myi.read(1) << endl;
76   return 0;
77 }

---

 1 // Error
 2 #include <fstream>
 3 #include<iostream>
 4 #include <cstdlib>
 5 #include<cstring>
 6 using namespace std;
 7 template<typename T> class myArray{
 8    fstream f1;
 9    public:
10    myArray(const string fname="temp1.in"){
11      f1.open(fname,ios::in|ios::out|ios::binary);
12      if(!f1){
13        f1.open(fname, ios::out | ios::binary);
14        if(!f1)
15           throw fname + "Can not open file";
16        else{
17          f1.close();
18          f1.open(fname, ios::in | ios::out | ios::binary);
19         }
20      }
21    }
22    ~myArray(){ f1.close();}
23    T read(int index){
24      T j;
25      f1.seekg(index * sizeof(T), ios::beg);
26      f1.read((char*) &j, sizeof(T));
27      return j;
28    }
29    void write(T j, int index){
30      f1.seekp(index * sizeof(T), ios::beg);
31      f1.write((char*) &j, sizeof(T));
32    }
33    T readNext(void){
34      T j;
35      f1.read((char*) &j, sizeof(T));
36      return j;
37    }
38    void writeNext(T j){
39      f1.write((char*) &j, sizeof(T));
40      f1.flush();
41    }
42    void rewind(void){
43      f1.seekg(0, ios::beg);
44      f1.seekp(0, ios::beg);}
45  };
46 struct student{
47   char name[20];
48   char stdno[14];
49   double avg;
50   friend ostream& operator<<(ostream& o1, student m1){
51     o1<<"( "<<m1.name<<" , "<<m1.stdno<<
52     " , "<<m1.avg<<" ) ";
53     return o1;
54   }
55   char& operator[](int index){
56     if(unsigned(index) < strlen(stdno))
57       return stdno[index];
58     return stdno[0];
59   }
60 };
61 int main(){
62   myArray<student> myi("temp6.in");
63   student st1 = {"Ali", "933424", 15.1};
64   int a = 1;
65   cout << st1[a] << endl;
66   //st1[1]='2';
67   st1.operator[](1) = '2';
68   myi.writeNext(st1);
69   strcpy(st1.name, "Reza");
70   strcpy(st1.stdno, "923434");
71   st1.avg = 14.2;
72   myi.writeNext(st1);
73   myi.rewind();
74   cout << myi.readNext() << endl;
75   cout << myi.readNext() << endl;
76   cout << myi.read(0) << endl;
77   cout << myi.read(1) << endl;
78   return 0;
79 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T> class myArray{
 7   fstream f1;
 8   public:
 9   myArray(const string fname = "temp1.in"){
10     f1.open(fname, ios::in | ios::out | ios::binary);
11     if(!f1){
12       f1.open(fname, ios::out | ios::binary);
13       if(!f1)
14         throw fname + "Can not open file";
15       else{
16         f1.close();
17         f1.open(fname, ios::in | ios::out | ios::binary);
18       }
19     }
20   }
21   ~myArray(){f1.close();}
22   T read(int index){
23     T j;
24     f1.seekg(index * sizeof(T), ios::beg);
25     f1.read((char*) &j, sizeof(T));
26     return j;
27   }
28   void write(T j, int index){
29     f1.seekp(index * sizeof(T), ios::beg);
30     f1.write((char*) &j, sizeof(T));
31   }
32   T readNext(void){
33     T j;
34     f1.read((char*) &j, sizeof(T));
35     return j;
36   }
37   void writeNext(T j){
38     f1.write((char*) &j, sizeof(T));
39     f1.flush();
40   }
41   void rewind(void){
42     f1.seekg(0, ios::beg);
43     f1.seekp(0, ios::beg);
44   }
45  };
46 struct student{
47   char name[20];
48   char stdno[14];
49   double avg;
50   friend ostream& operator<<(ostream& o1, const student& m1){
51     o1 << "( " << m1.name << " , " << m1.stdno
52       << " , " << m1.avg << " ) ";
53     return o1;
54   }
55   char& operator[](int index){
56     if(index >= 0 && unsigned(index) < strlen(stdno))
57       return stdno[index];
58     return stdno[0];
59   }
60 };
61 int main(){
62   myArray<student> myi("temp6.in");
63   student st1={"Ali", "933424", 15.1};
64   int a=1;
65   cout << st1[a] << endl;
66   st1[1] = '2';
67   st1.operator[](1) = '2';
68   myi.writeNext(st1);
69   strcpy(st1.name, "Reza");
70   strcpy(st1.stdno, "923434");
71   st1.avg = 14.2;
72   myi.writeNext(st1);
73   myi.rewind();
74   cout << myi.readNext() << endl;
75   cout << myi.readNext() << endl;
76   cout <<myi.read(0) << endl;
77   cout << myi.read(1) << endl;
78   return 0;
79 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include<cstring>
 4 using namespace std;
 5 template<typename T> class myArray{
 6   fstream f1;
 7   public:
 8   myArray(const string fname = "temp1.in"){
 9     f1.open(fname, ios::in | ios::out | ios::binary);
10     if(!f1){
11       f1.open(fname, ios::out | ios::binary);
12       if(!f1)
13         throw fname + " Can not open file";
14       else{
15          f1.close();
16          f1.open(fname, ios::in | ios::out | ios::binary);
17       }
18     }
19   }
20   ~myArray(){f1.close();}
21   T read(int index){
22     T j;
23     f1.seekg(index * sizeof(T), ios::beg);
24     f1.read((char*) &j, sizeof(T));
25     return j;
26   }
27   void write(T j, int index){
28     f1.seekp(index * sizeof(T), ios::beg);
29     f1.write((char*) &j, sizeof(T));
30   }
31   T readNext(void){
32     T j;
33     f1.read((char*) &j, sizeof(T));
34     return j;
35   }
36   void writeNext(T j){
37     f1.write((char*) &j, sizeof(T));
38     f1.flush();
39   }
40   void rewind(void){
41     f1.seekg(0, ios::beg);
42     f1.seekp(0, ios::beg);
43   }
44  };
45 struct student{
46   char name[20];
47   char stdno[14];
48   double avg;
49   friend ostream& operator<<(ostream & o1, student m1){
50     o1 << "( " << m1.name << " , " << m1.stdno
51       << " , " << m1.avg << " ) ";
52     return o1;
53   }
54   char& operator[](int index){
55     if(index >= 0 && unsigned(index) < strlen(stdno))
56       return stdno[index];
57     return stdno[0];
58   }
59 };
60 int main(){
61   myArray<student> myi("temp6.in");
62   student st1 = {"Ali", "933424", 15.1};
63   int a=1;
64   cout << st1 << endl;
65   cout << st1[a] << endl;
66   st1[1] = '2';
67   st1.operator[](1) = '2';
68   myi.writeNext(st1);
69   strcpy(st1.name, "Reza");
70   strcpy(st1.stdno, "923434");
71   st1.avg = 14.2;
72   myi.writeNext(st1);
73   myi.rewind();
74   cout << myi.readNext() << endl;
75   cout << myi.readNext() << endl;
76   cout << myi.read(0) << endl;
77   cout << myi.read(1) << endl;
78   return 0;
79 }

---

 1 // Error
 2 #include <fstream>
 3 #include<iostream>
 4 #include <cstdlib>
 5 #include<cstring>
 6 using namespace std;
 7 //void *
 8 //char *
 9 //int ff3(void * hh);
10 //int ff4(char * hh);
11 template<typename T>
12 class myArray{
13    fstream f1;
14    public:
15    myArray(const char *fname="temp1.in"){
16      f1.open(fname,ios::in|ios::out|ios::binary);
17      if(!f1){
18        f1.open(fname,ios::out|ios::binary);
19        if(!f1){ cout<<"Can not open file"<<endl; exit(0);}
20        else{f1.close(); f1.open(fname,ios::in|ios::out|ios::binary);}
21      }
22    }
23    ~myArray(){ f1.close();}
24    T read(int index){
25      T j;
26      f1.seekg(index*sizeof(T),ios::beg); // ios::end   ios::cur
27      f1.read((char *)&j , sizeof(T));
28      return j;
29    }
30    void write(T j, int index){
31      f1.seekp(index*sizeof(T),ios::beg);
32      f1.write((char *) &j , sizeof(T));
33    }
34    T readNext(void){
35      T j;
36      f1.read((char *)&j , sizeof(T));
37      return j;
38    }
39    void writeNext(T j){
40      f1.write((char *)&j, sizeof(T));
41      f1.flush();
42    }
43    void rewind(void){ f1.seekg(0,ios::beg);f1.seekp(0,ios::beg);}
44  };
45 struct student{
46   char name[20];
47   char stdno[14];
48   double avg;
49   // Error
50   //friend ostream& operator<<(ostream & o1, student &);
51   friend ostream& operator<<(ostream & o1, student &);
52   char & operator[](int  index);
53 };
54 int mystrlen(char *s){int i;for(i=0;s[i];i++); return i;}
55 //if(unsigned(index)<strlen(stdno)) return stdno[index];
56 char & student::operator[](int  index){
57   if(index<mystrlen(stdno)) return stdno[index];
58   return stdno[0];
59 }
60 // Error
61 //ostream& operator<<(ostream & o1, student & m1){
62 ostream& operator<<(ostream & o1, student & m1){
63   o1<<"( "<<m1.name<<" , "<<m1.stdno<<
64   " , "<<m1.avg<<" ) ";
65   return o1;
66 }
67 int main(){//myArray<student> myi("temp6.in");
68   student st1={"Ali","933424",15.1};int a=1;
69   cout<<st1<<endl;operator<<(cout,st1);
70   cout<<st1[a]<<endl; st1[1]='2'; st1.operator[](1) = '2';
71   cout<<st1;
72   /*myi.writeNext(st1);
73   strcpy(st1.name,"Reza");strcpy(st1.stdno,"923434");
74   st1.avg=14.2; myi.writeNext(st1); myi.rewind();
75   cout<<myi.readNext()<<endl;
76   //operator<<(cout,myi.readNext());
77   //student *ps= & myi.readNext(); Error
78   cout<<myi.readNext()<<endl<<endl;
79   cout<<myi.read(0)<<endl;
80   cout<<myi.read(1)<<endl;
81   //myi.write(54,10);
82   //cout<<myi.read(25)<<endl<<endl;
83   */return 0;
84 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 //void *
 7 //char *
 8 //int ff3(void * hh);
 9 //int ff4(char * hh);
10 template<typename T>
11 class myArray{
12    fstream f1;
13    public:
14    myArray(const char *fname="temp1.in"){
15      f1.open(fname,ios::in|ios::out|ios::binary);
16      if(!f1){
17        f1.open(fname,ios::out|ios::binary);
18        if(!f1){ cout<<"Can not open file"<<endl; exit(0);}
19        else{f1.close(); f1.open(fname,ios::in|ios::out|ios::binary);}
20      }
21    }
22    ~myArray(){ f1.close();}
23    T read(int index){
24      T j;
25      f1.seekg(index*sizeof(T),ios::beg); // ios::end   ios::cur
26      f1.read((char *)&j , sizeof(T));
27      return j;
28    }
29    void write(T j, int index){
30      f1.seekp(index*sizeof(T),ios::beg);
31      f1.write((char *) &j , sizeof(T));
32    }
33    T readNext(void){
34      T j;
35      f1.read((char *)&j , sizeof(T));
36      return j;
37    }
38    void writeNext(T j){
39      f1.write((char *)&j, sizeof(T));
40      f1.flush();
41    }
42    void rewind(void){ f1.seekg(0,ios::beg);f1.seekp(0,ios::beg);}
43  };
44 struct student{
45   char name[20];
46   char stdno[14];
47   double avg;
48   // Error
49   //friend ostream& operator<<(ostream & o1, student &);
50   friend ostream& operator<<(ostream & o1, student );
51   char & operator[](int  index);
52 };
53 int mystrlen(char *s){int i;for(i=0;s[i];i++); return i;}
54 //if(unsigned(index)<strlen(stdno)) return stdno[index];
55 char & student::operator[](int  index){
56   if(index<mystrlen(stdno)) return stdno[index];
57   return stdno[0];
58 }
59 // Error
60 //ostream& operator<<(ostream & o1, student & m1){
61 ostream& operator<<(ostream & o1, student  m1){
62   o1<<"( "<<m1.name<<" , "<<m1.stdno<<
63   " , "<<m1.avg<<" ) ";
64   return o1;
65 }
66 int main(){//myArray<student> myi("temp6.in");
67   student st1={"Ali","933424",15.1};int a=1;
68   cout<<st1<<endl;operator<<(cout,st1);
69   cout<<st1[a]<<endl; st1[1]='2'; st1.operator[](1) = '2';
70   myi.writeNext(st1);
71   strcpy(st1.name,"Reza");strcpy(st1.stdno,"923434");
72   st1.avg=14.2; myi.writeNext(st1); myi.rewind();
73   cout<<myi.readNext()<<endl;
74   //operator<<(cout,myi.readNext());
75   //student *ps= & myi.readNext(); Error
76   cout<<myi.readNext()<<endl<<endl;
77   cout<<myi.read(0)<<endl;
78   cout<<myi.read(1)<<endl;
79   //myi.write(54,10);
80   //cout<<myi.read(25)<<endl<<endl;
81   return 0;
82 }

---

 1 #include <fstream>
 2 #include<iostream>
 3 #include <cstdlib>
 4 #include<cstring>
 5 using namespace std;
 6 template<typename T>class myFileArray{fstream f1;
 7    public:
 8    myFileArray(const char *fname="temp1.in"){
 9      f1.open(fname,ios::in|ios::out|ios::binary);
10      if(!f1){
11        f1.open(fname,ios::out|ios::binary);
12        if(!f1){ cout<<"Can not open file"<<endl; exit(0);}
13        else{f1.close(); f1.open(fname,ios::in|ios::out|ios::binary);}
14      }
15    }
16    ~myFileArray(){ f1.close();}
17    T read(int index){
18      T j;
19      f1.seekg(0,ios::end);
20      long long int l1=f1.tellg();
21      l1 /= sizeof(T);
22      if(index>=l1){cout<<"Index is out of range\n";exit(0);}
23      f1.seekg(index*sizeof(T),ios::beg); // ios::end   ios::cur
24      f1.read((char *)&j , sizeof(T));
25      return j;
26    }
27    void write(T j, int index){
28      f1.seekg(0,ios::end);
29      long long int l1=f1.tellg();
30      l1 /= sizeof(T);
31      if(index>l1){cout<<"Index is out of range\n";exit(0);}
32      f1.seekp(index*sizeof(T),ios::beg);
33      f1.write((char *) &j , sizeof(T));
34    }
35    T readNext(void){
36      T j;
37      long long int pos=f1.tellg();
38      f1.seekg(0,ios::end);
39      long long int l1=f1.tellg();
40      if(pos == l1)
41      {cout<<"Index is out of range\n";exit(0);}
42      f1.seekg(pos,ios::beg);
43      f1.read((char *)&j , sizeof(T));
44      return j;
45    }
46    void writeNext(T j){
47      f1.write((char *)&j, sizeof(T));
48      f1.flush();
49    }
50    void rewind(void){ f1.seekg(0,ios::beg);f1.seekp(0,ios::beg);}
51  };
52 struct student{
53   char name[20];
54   char stdno[14];
55   double avg;
56   // Error
57   //friend ostream& operator<<(ostream & o1, student &);
58   friend ostream& operator<<(ostream & o1, student );
59   char & operator[](int  index);
60 };
61 int mystrlen(char *s){int i;for(i=0;s[i];i++); return i;}
62 //if(unsigned(index)<strlen(stdno)) return stdno[index];
63 char & student::operator[](int  index){
64   if(index<mystrlen(stdno)) return stdno[index];
65   return stdno[0];
66 }
67 // Error
68 //ostream& operator<<(ostream & o1, student & m1){
69 ostream& operator<<(ostream & o1, student  m1){
70   o1<<"( "<<m1.name<<" , "<<m1.stdno<<
71   " , "<<m1.avg<<" ) ";
72   return o1;
73 }
74 int main(){myFileArray<student> myi("temp6.in");
75   student st1={"Ali","933424",15.1};int a=1;
76   cout<<st1<<endl;operator<<(cout,st1);
77   cout<<st1[a]<<endl; st1[1]='2'; st1.operator[](1) = '2';
78   myi.writeNext(st1);
79   strcpy(st1.name,"Reza");strcpy(st1.stdno,"923434");
80   st1.avg=14.2; myi.writeNext(st1); myi.rewind();
81   cout<<myi.readNext()<<endl;
82   //operator<<(cout,myi.readNext());
83   //student *ps= & myi.readNext(); Error
84   cout<<myi.readNext()<<endl<<endl;
85   cout<<myi.read(0)<<endl;
86   cout<<myi.read(1)<<endl;
87   myi.write(st1,10);
88   cout<<myi.read(25)<<endl<<endl;
89   return 0;
90 }

---

  1 #include <fstream>
  2 #include<iostream>
  3 #include <cstdlib>
  4 #include<cstring>
  5 using namespace std;
  6 template<typename T> struct write_type{T data;int index;};
  7 template<typename T>class myFileArray{
  8   fstream f1;
  9   public:
 10   myFileArray(const char *fname="temp1.in"){
 11      f1.open(fname,ios::in|ios::out|ios::binary);
 12      if(!f1){
 13        f1.open(fname,ios::out|ios::binary);
 14        if(!f1){ cout<<"Can not open file"<<endl; exit(0);}
 15        else{f1.close(); f1.open(fname,ios::in|ios::out|ios::binary);}
 16     }
 17    }
 18    ~myFileArray(){ f1.close();}
 19    T read(int index){
 20      T j;
 21      f1.seekg(0,ios::end);
 22      long long int l1=f1.tellg();
 23      l1 /= sizeof(T);
 24      if(index>=l1){cout<<"Index is out of range\n"; throw 2;}
 25      f1.seekg(index*sizeof(T),ios::beg); // ios::end   ios::cur
 26      f1.read((char *)&j , sizeof(T));
 27      return j;
 28    }
 29    void write(T j, int index){
 30      f1.seekg(0,ios::end);
 31      long long int l1=f1.tellg();
 32      l1 /= sizeof(T);
 33      if(index>l1){cout<<"Index is out of range\n";exit(0);}
 34      f1.seekp(index*sizeof(T),ios::beg);
 35      f1.write((char *) &j , sizeof(T));
 36    }
 37    T readNext(void){
 38      T j;
 39      long long int pos=f1.tellg();
 40      f1.seekg(0,ios::end);
 41      long long int l1=f1.tellg();
 42      if(pos == l1)
 43      {cout<<"Index is out of range\n";exit(0);}
 44      f1.seekg(pos,ios::beg);
 45      f1.read((char *)&j , sizeof(T));
 46      return j;
 47    }
 48    T& operator[](int index){
 49      static T j;
 50      f1.seekg(0,ios::end);
 51      long long int l1=f1.tellg();
 52      l1 /= sizeof(T);
 53      if(index>=l1){cout<<"Index is out of range\n";exit(0);}
 54      f1.seekg(index*sizeof(T),ios::beg); // ios::end   ios::cur
 55      f1.read((char *)&j , sizeof(T));
 56      return j;
 57    }
 58    const T& operator[](const write_type<T> &idx){ // a[complexCls(2,3)]
 59      f1.seekg(0,ios::end);
 60      long long int l1=f1.tellg();
 61      l1 /= sizeof(T);
 62      if(idx.index>l1){cout<<"Index is out of range\n";exit(0);}
 63      f1.seekp(idx.index*sizeof(T),ios::beg);
 64      f1.write((char *) &idx.data , sizeof(T));
 65      return idx.data;
 66    }
 67    void writeNext(T j){
 68      f1.write((char *)&j, sizeof(T));
 69      f1.flush();
 70    }
 71    void rewind(void){ f1.seekg(0,ios::beg);f1.seekp(0,ios::beg);}
 72  };
 73 struct student{
 74   char name[20];
 75   char stdno[14];
 76   double avg;
 77   // Error
 78   //friend ostream& operator<<(ostream & o1, student &);
 79   friend ostream& operator<<(ostream & o1, student );
 80   char & operator[](int  index);
 81 };
 82 int mystrlen(char *s){int i;for(i=0;s[i];i++); return i;}
 83 //if(unsigned(index)<strlen(stdno)) return stdno[index];
 84 char & student::operator[](int  index){
 85   if(index<mystrlen(stdno)) return stdno[index];
 86   return stdno[0];
 87 }
 88 // Error
 89 //ostream& operator<<(ostream & o1, student & m1){
 90 ostream& operator<<(ostream & o1, student  m1){
 91   o1<<"( "<<m1.name<<" , "<<m1.stdno<<
 92   " , "<<m1.avg<<" ) ";
 93   return o1;
 94 }
 95 int main(){myFileArray<student> myi("temp6.in");
 96   student st1={"Ali","933424",15.1};int a=1;
 97   student st2={"Kamran","68588",12.1};
 98   write_type<student> wt1{st2,0};
 99   cout<<st1<<endl;operator<<(cout,st1);
100   cout<<st1[a]<<endl; st1[1]='2'; st1.operator[](1) = '2';
101   myi.writeNext(st1);
102   strcpy(st1.name,"Reza");strcpy(st1.stdno,"923434");
103   st1.avg=14.2; myi.writeNext(st1); myi.rewind();
104   cout<<myi.readNext()<<endl;
105   //operator<<(cout,myi.readNext());
106   //student *ps= & myi.readNext(); Error
107   cout<<myi.readNext()<<endl<<endl;
108   cout<<myi.read(0)<<endl;
109   cout<<"myi[0]"<<endl;
110   cout<<myi[0]<<endl;
111   cout<<myi.read(1)<<endl;
112   cout<<"myi[1]"<<endl;
113   cout<<myi[1]<<endl;
114   cout<<myi[wt1]<<endl;
115   cout<<myi.read(0)<<endl<<endl;
116   return 0;
117 }

---

  1 #include <fstream>
  2 #include<iostream>
  3 #include <cstdlib>
  4 #include<cstring>
  5 using namespace std;
  6 template<typename T>class myFileArray{fstream f1;
  7    public:
  8    myFileArray(const char *fname="temp1.in"){
  9      f1.open(fname,ios::in|ios::out|ios::binary);
 10      if(!f1){
 11        f1.open(fname,ios::out|ios::binary);
 12        if(!f1){ cout<<"Can not open file"<<endl; exit(0);}
 13        else{f1.close(); f1.open(fname,ios::in|ios::out|ios::binary);}
 14     }
 15    }
 16    ~myFileArray(){ f1.close();}
 17    T read(int index){
 18      T j;
 19      f1.seekg(0,ios::end);
 20      long long int l1=f1.tellg();
 21      l1 /= sizeof(T);
 22      if(index>=l1){cout<<"Index is out of range\n";exit(0);}
 23      f1.seekg(index*sizeof(T),ios::beg); // ios::end   ios::cur
 24      f1.read((char *)&j , sizeof(T));
 25      return j;
 26    }
 27    void write(T j, int index){
 28      f1.seekg(0,ios::end);
 29      long long int l1=f1.tellg();
 30      l1 /= sizeof(T);
 31      if(index>l1){cout<<"Index is out of range\n";exit(0);}
 32      f1.seekp(index*sizeof(T),ios::beg);
 33      f1.write((char *) &j , sizeof(T));
 34    }
 35    T readNext(void){
 36      T j;
 37      long long int pos=f1.tellg();
 38      f1.seekg(0,ios::end);
 39      long long int l1=f1.tellg();
 40      if(pos == l1)
 41      {cout<<"Index is out of range\n";exit(0);}
 42      f1.seekg(pos,ios::beg);
 43      f1.read((char *)&j , sizeof(T));
 44      return j;
 45    }
 46    T& operator[](int index){
 47      static T j;
 48      f1.seekg(0,ios::end);
 49      long long int l1=f1.tellg();
 50      l1 /= sizeof(T);
 51      if(index>=l1){cout<<"Index is out of range\n";exit(0);}
 52      f1.seekg(index*sizeof(T),ios::beg); // ios::end   ios::cur
 53      f1.read((char *)&j , sizeof(T));
 54      return j;
 55    }
 56    const T& operator[](int index){
 57      static T j;
 58      f1.seekg(0,ios::end);
 59      long long int l1=f1.tellg();
 60      l1 /= sizeof(T);
 61      if(index>l1){cout<<"Index is out of range\n";exit(0);}
 62      f1.seekp(index*sizeof(T),ios::beg);
 63      f1.write((char *) &j , sizeof(T));
 64    }
 65    void writeNext(T j){
 66      f1.write((char *)&j, sizeof(T));
 67      f1.flush();
 68    }
 69    void rewind(void){ f1.seekg(0,ios::beg);f1.seekp(0,ios::beg);}
 70  };
 71 struct student{
 72   char name[20];
 73   char stdno[14];
 74   double avg;
 75   // Error
 76   //friend ostream& operator<<(ostream & o1, student &);
 77   friend ostream& operator<<(ostream & o1, student );
 78   char & operator[](int  index);
 79 };
 80 int mystrlen(char *s){int i;for(i=0;s[i];i++); return i;}
 81 //if(unsigned(index)<strlen(stdno)) return stdno[index];
 82 char & student::operator[](int  index){
 83   if(index<mystrlen(stdno)) return stdno[index];
 84   return stdno[0];
 85 }
 86 // Error
 87 //ostream& operator<<(ostream & o1, student & m1){
 88 ostream& operator<<(ostream & o1, student  m1){
 89   o1<<"( "<<m1.name<<" , "<<m1.stdno<<
 90   " , "<<m1.avg<<" ) ";
 91   return o1;
 92 }
 93 int main(){myFileArray<student> myi("temp6.in");
 94   student st1={"Ali","933424",15.1};int a=1;
 95   cout<<st1<<endl;operator<<(cout,st1);
 96   cout<<st1[a]<<endl; st1[1]='2'; st1.operator[](1) = '2';
 97   myi.writeNext(st1);
 98   strcpy(st1.name,"Reza");strcpy(st1.stdno,"923434");
 99   st1.avg=14.2; myi.writeNext(st1); myi.rewind();
100   cout<<myi.readNext()<<endl;
101   //operator<<(cout,myi.readNext());
102   //student *ps= & myi.readNext(); Error
103   cout<<myi.readNext()<<endl<<endl;
104   cout<<myi.read(0)<<endl;
105   cout<<"myi[0]"<<endl;
106   cout<<myi[0]<<endl;
107   cout<<myi.read(1)<<endl;
108   cout<<"myi[1]"<<endl;
109   cout<<myi[1]<<endl;
110   myi.write(st1,10);
111   myi[10]=st1;
112   cout<<myi.read(25)<<endl<<endl;
113   return 0;
114 }

---

 1 #include <iostream>
 2 #include <fstream>
 3 #include <sstream>
 4 #include <string>
 5 #include <cstdint>
 6 int main(){ // https://en.cppreference.com/w/cpp/io/basic_istream/read
 7   // read() is often used for binary I/O
 8   std::string bin = {'\x12', '\x12', '\x12', '\x12'};
 9   std::istringstream raw(bin);
10   std::uint32_t n;
11   if(raw.read(reinterpret_cast<char*>(&n), sizeof n))
12     std::cout << std::hex << std::showbase << n << '\n';
13 
14   // prepare file for next snippet
15   std::ofstream("test.txt", std::ios::binary) << "abcd1\nabcd2\nabcd3";
16 
17   // read entire file into string
18   if(std::ifstream is{"test.txt", std::ios::binary | std::ios::ate}) {
19     auto size = is.tellg();
20     std::string str(size, '\0'); // construct string to stream size
21     is.seekg(0);
22     if(is.read(&str[0], size))
23         std::cout << str << '\n';
24   }
25 }
26 /* https://en.cppreference.com/w/cpp/io/basic_ostream/write
27 #include <iostream>
28 int main(){
29   int n = 0x41424344;
30   std::cout.write(reinterpret_cast<char*>(&n), sizeof n) << '\n';
31 
32   char c[]="This is sample text.";
33   std::cout.write(c, 4).write("!\n", 2);
34 }
35 */
36 /* https://en.cppreference.com/w/cpp/io/basic_ifstream
37 #include <iostream>
38 #include <fstream>
39 #include <string>
40 int main() {
41   std::string filename = "Test.b";
42   // prepare a file to read
43   double d = 3.14;
44   std::ofstream(filename, std::ios::binary).write(reinterpret_cast<char*>(&d), sizeof d)
45      << 123 << "abc";
46   // open file for reading
47   std::ifstream istrm(filename, std::ios::binary);
48   if (!istrm.is_open()) {
49     std::cout << "failed to open " << filename << '\n';
50   } else {
51     double d;
52     istrm.read(reinterpret_cast<char*>(&d), sizeof d); // binary input
53     int n;
54     std::string s;
55     if (istrm >> n >> s)                               // text input
56       std::cout << "read back from file: " << d << ' ' << n << ' ' << s << '\n';
57   }
58 }
59 */

---

 1 #include<iostream>
 2 #include<fstream>
 3 using namespace std;
 4 struct myMat{int n; double**p;};
 5 myMat read(const char *name){
 6   myMat m;m.n=0;m.p=0;double *pd=0;
 7   ifstream f(name);
 8   if(!f){cout<<"cannot open file"<<endl;return m;}
 9   f.read((char*)&m.n,sizeof(int));
10   pd=new double[m.n*m.n];
11   f.read((char*)pd,sizeof(double)*m.n*m.n);
12   f.close();
13   m.p=new double*[m.n];
14   for(int i=0;i<m.n;i++){
15     m.p[i]=new double[m.n];
16     for(int j=0;j<m.n;j++)
17       m.p[i][j]=pd[i*m.n+j];
18   }
19   delete[]pd;
20   f.close();
21   return m;
22 }
23 bool write(const char*name,myMat m){
24   ofstream  f1(name);
25   if(!f1){cout<<"cannot open file"<<endl;return false;}
26   double*pd=new double[m.n*m.n];
27   for(int i=0;i<m.n;i++)
28     for(int j=0;j<m.n;j++)
29       pd[i*m.n+j]=m.p[i][j];
30   f1.write((char*)&m.n,sizeof(int));
31   f1.write((char*)pd,sizeof(double)*m.n*m.n);
32   f1.close();
33   return true;
34 }
35 struct mat2{int n; double p[100][100];};
36 mat2  read2(const char*name){
37   mat2 m; m.n=0;
38   ifstream f(name);
39   if(!f){cout<<""<<endl;exit(0);}
40   f.read((char*)&m.n,sizeof(int));
41   for(int i=0;i<n;i++)
42     for(int j=0;j<n;j++)
43       f.read((char*)&m.p[i][j],sizeof(double));
44   f.close();
45 }
46 bool write2(const char*name,mat2 m){
47   ofstream  f1(name);
48   if(!f1){cout<<"cannot open file"<<endl;return false;}
49   f1.write((char*)&m.n,sizeof(int));
50   for(int i=0;i<m.n;i++)
51     for(int j=0;j<m.n;j++)
52       f1.write((char*)&m.p[i][j],sizeof(double));
53   f1.close();
54   return true;
55 }
56 myMat input(void){
57   int i,j;myMat m;
58   cout<<"enter n "; cin>>m.n;
59   m.p=new double*[m.n];
60   for(i=0;i<m.n;i++){
61     m.p[i]=new double[m.n];
62     for(j=0;j<m.n;j++){
63       cout<<"enter a["<<i<<"]["<<j<<"]:";
64       cin>>m.p[i][j];
65     }
66   }
67   return m;
68 }
69 void print(myMat m){
70   int i,j;cout<<m.n<<endl;
71   for(i=0;i<m.n;i++){
72     for(j=0;j<m.n;j++) cout<<m.p[i][j]<<'\t';
73     cout<<endl;
74   }
75 }
76 myMat mult(myMat m1, myMat m2){
77   myMat m3;m3.n=m1.n;m3.p=new double*[m1.n];
78   for(int i=0;i<m1.n;i++){
79     m3.p[i]=new double[m1.n];
80     for(int j=0;j<m1.n;j++){
81       double sum=0;
82       for(int k=0;k<m1.n;k++) sum+=m1.p[i][k]*m2.p[k][j];
83       m3.p[i][j]=sum;
84     }
85   }
86   return m3;
87 }
88 int main(){
89   //myMat m1,m2; m1=input();m2=input();write("mat1.in",m1);write("mat2.in",m2);
90   myMat m1=read("mat1.in"),m2=read("mat2.in"),m3;
91   print(m1);print(m2);
92   m3=mult(m1,m2);
93   write("mat3.in",m3);
94   print(m3);
95   return 0;
96 }

---

END

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