'read': identifier not found, short code plz help

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  12 years ago

  by anh85

  thai anh

  , Viet Nam

  Joined 12 years ago
  im just trying to get the hang of binary file io by making a simple program that can write a structure into a file, then read it, but the first error message i get is
  
  'read': identifier not found
  
  heres the code:
  
  [CODE]#include <iostream>
  #include <fstream>
  using namespace std;
  
  struct grades
  {
      int grade1;
      int grade2;
      int grade3;
      int grade4;
  } mygradesi,mygradeso;
  
  int main ()
  {
      int answer;
      do
      {
          cout<<"do u want to 1, write to the file or 2, read from the file, or 3, exit the program?";
          cin>>answer;
          if (answer==2)
          {
              struct grades * mygradesptri;
              mygradesptri=&mygradesi;
              ifstream myfilei;
              myfilei.open ("binary.bin", ios::in|ios::binary);
              if (myfilei.is_open())
              {
                  read(mygradesptri, sizeof(grades));
                  cout<< mygradesi.grade1<< mygradesi.grade2<< mygradesi.grade3<< mygradesi.grade4;
              }
              else cout << "Unable to open file for input";
          }
          if (answer==1)
          {
              struct grades * mygradesptro;
              mygradesptro=&mygradeso;
              ofstream myfileo;
              myfileo.open ("binary.bin", ios::out|ios::binary);
              cout>>"please enter 4 grades";
              cin<< mygradeso.grade1<< mygradeso.grade2<< mygradeso.grade3<< mygradeso.grade4;
              if (myfileo.is_open())
              {
                  write (mygradesptro, sizeof(grades));
                  myfileo.close();
              }
              else cout << "Unable to open file for output";
          }
      }while (answer!=3);
      return 0;
  }    [/CODE]
  
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  12 years ago

  by anh85

  thai anh

  , Viet Nam

  Joined 12 years ago

  how silly of me, i did not specify the name of the class. i ran into a new problem though, read and write are supposed to take char *, but im not trying to pass a char, im trying to pass a structure pointer, how do i do that?
  
  error says cannot convert grades * to char *
  
  [CODE]
  #include <iostream>
  #include <fstream>
  using namespace std;
  
  struct grades
  {
      int grade1;
      int grade2;
      int grade3;
      int grade4;
  } mygradesi,mygradeso;
  
  int main ()
  {
      int answer;
      do
      {
          cout<<"do u want to 1, write to the file or 2, read from the file, or 3, exit the program?";
          cin>>answer;
          if (answer==2)
          {
              char * mygradesptri;
              mygradesptri=&mygradesi;
              ifstream myfilei;
              myfilei.open ("binary.bin", ios::in|ios::binary);
              if (myfilei.is_open())
              {
                  myfilei.read(mygradesptri, sizeof(grades));
                  cout<< mygradesi.grade1<< mygradesi.grade2<< mygradesi.grade3<< mygradesi.grade4;
              }
              else cout << "Unable to open file for input";
          }
          if (answer==1)
          {
              char * mygradesptro;
              mygradesptro=&mygradeso;
              ofstream myfileo;
              myfileo.open ("binary.bin", ios::out|ios::binary);
              cout>>"please enter 4 grades";
              cin<< mygradeso.grade1<< mygradeso.grade2<< mygradeso.grade3<< mygradeso.grade4;
              if (myfileo.is_open())
              {
                  myfileo.write (mygradesptro, sizeof(grades));
                  myfileo.close();
              }
              else cout << "Unable to open file for output";
          }
      }while (answer!=3);
      return 0;
  }   
  [/CODE]
  

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  12 years ago

  by Mohammad Rastkar

  Mohammad Rastkar

  Shiraz, Iran

  Joined 14 years ago

  Hi ,

  Just cast to (char *), explicitly :

  myfilei.read( (char *)mygradesptri, sizeof(grades) );

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• • Reply

  12 years ago

  by anh85

  thai anh

  , Viet Nam

  Joined 12 years ago

   ty! works perfectly! ur the best!
  

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