Putting a structure into a file

This is a discussion on Putting a structure into a file within the C++ Programming forums, part of the General Programming Boards category; I have a structure i need put into a file I know that you can do binary files but when ...

  1. #1
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    Putting a structure into a file

    I have a structure i need put into a file I know that you can do binary files but when i use fopen, fwrite, the open works but fwrite always causes the program to crash. Can someone post an example of creating, writing and reading a structure from a binary file?

  2. #2
    Confused Magos's Avatar
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    Why don't you post your code that crashes? That way we can see whats wrong.

    And this topic should be in the C forums.
    MagosX.com

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  3. #3
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    Code:
    FILE *stream;
     if ((stream = fopen("binary.dat", "wb")) != NULL)
     {
       fwrite(&data_struct, sizeof(data_struct), 1, stream); // write struct s to file
       fclose(stream);
     }

  4. #4
    Confused Magos's Avatar
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    Hmm, that looks correct, assuming that your structure is...

    Here is a write/read sample which works for me: try and compile it. If it crashes it must be something with your compiler or OS.
    Code:
    #include <stdio.h>
    #include <conio.h>
    
    typedef struct
    {
       int Var1;
    }MYSTRUCTURE;
    
    int main()
    {
       MYSTRUCTURE Structure1;
       FILE* WriteFile;
       Structure1.Var1=12345;
    
       WriteFile=fopen("Myfile.tmp", "wb");
       if(WriteFile!=NULL)
       {
          //Write data
          fwrite(&Structure1, sizeof(MYSTRUCTURE), 1, WriteFile);
          fclose(WriteFile);
       }
       else
       {
          //Error
          printf("Error writing file!");
          getch();
          return 0;
       }
    
       MYSTRUCTURE Structure2;
       FILE* ReadFile;
    
       ReadFile=fopen("Myfile.tmp", "rb");
       if(ReadFile!=NULL)
       {
          //Read data
          fread(&Structure2, sizeof(MYSTRUCTURE), 1, ReadFile);
          fclose(ReadFile);
       }
       else
       {
          //Error
          printf("Error reading file!");
          getch();
          return 0;
       }
    
       //Print the result
       printf("value: %d", Structure2.Var1);
       getch();
       return 0;
    }

  5. #5
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    Code:
    ifstream fin;
    fin.open("filenamehere");
    fin>>data_struct;
    fin.close();
    the include file is process.h




    ... damn you guys try too hard. its this simple
    Last edited by Denethor2000; 04-22-2002 at 11:35 AM.

  6. #6
    Confused Magos's Avatar
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    Originally posted by Denethor2000
    Code:
    ifstream fin;
    open("filenamehere");
    fin>>data_struct;
    close();
    the include file is process.h
    This doesn't look right. Shouldn't the second line be
    fin.open("FileName.ext");
    And the last line be:
    fin.close();
    ???
    MagosX.com

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    Teach a man to fish and you feed him for a lifetime.

  7. #7
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    yeah i caught that
    its edited, refresh

  8. #8
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    Unregistered... you are welcome..... weeeeeeeell? if u ask around ull ifnd im very conscious of people being GRATEFUL, YOU UNG-... yeah. you're welcome

  9. #9
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    How can you add and load char[]'s to/from a structure then?

    Code:
    #include <stdio.h>
    #include <conio.h>
    
    typedef struct
    {
       char[10] Var1;
    }MYSTRUCTURE;
    
    int main()
    {
       MYSTRUCTURE Structure1;
       FILE* WriteFile;
       Structure1.Var1="sghrdhj";
    
       WriteFile=fopen("Myfile.tmp", "wb");
       if(WriteFile!=NULL)
       {
          //Write data
          fwrite(&Structure1, sizeof(MYSTRUCTURE), 1, WriteFile);
          fclose(WriteFile);
       }
       else
       {
          //Error
          printf("Error writing file!");
          getch();
          return 0;
       }
    
       MYSTRUCTURE Structure2;
       FILE* ReadFile;
    
       ReadFile=fopen("Myfile.tmp", "rb");
       if(ReadFile!=NULL)
       {
          //Read data
          fread(&Structure2, sizeof(MYSTRUCTURE), 1, ReadFile);
          fclose(ReadFile);
       }
       else
       {
          //Error
          printf("Error reading file!");
          getch();
          return 0;
       }
    
       //Print the result
       printf("value: %d", Structure2.Var1);
       getch();
       return 0;
    }
    Certainly doesn't work. Even if it did, the characters of the string would be read with their numerical values.

    I need to know how to do this because I want to add and load questions, example:

    Code:
    struct Database
    {
        int history_qs_n_ans_number;
    
        char history_qs[1000];
        char history_ans[1000];
        char note[1000];
    };
    
    Database Religious_history[] =
    {
    
      { 1, "Who founded the religion of Zoroastrianism?", "Zarathustra", "The belief of when Zarathustra, or Zoroaster lived, has varied greatly over the years, he is now dated to about 1000 BC. There are some people who even questionhis existence." },  // #1 initialized.
      { 2, "Which was the official religion in the empire of Han(206 BC - 220 AD)?", "Konfucianism", "Konfucianism remains from the belief of the philiosoph Konfucius" },  // #2 initialized.
      { 3, "Which year did Muhammed escape from Mecca?" }   // #3 initializexd.
    
    };
    How can all this succefully be added and loaded from/to a file?

  10. #10
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    > Structure1.Var1="sghrdhj";

    This should be:
    strcpy(Structure1.Var1,"sghrdhj");

  11. #11
    ATH0 quzah's Avatar
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    How can you add and load char[]'s to/from a structure then?
    Yeah but not the way you want. You can't use a static table like that. Well, you could:

    Code:
    struct mydata mytable[MYSIZE];
    for( x = 0; x < MYSIZE; x++ )
        fread( mytable[x], sizeof( struct mydate ), 1, fp );
    Or you could just use a linked list.

    Quzah.
    Hope is the first step on the road to disappointment.

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