Expert: Prince M. Premnath - 6/6/2007

Question
Hi,sir: Can you tell me why dont write "R" in simple follow code? im confused why fwrite function cant write 2 s.ch?!!
please help me:
#include <stdio.h>
#include<conio.h>
struct mystruct
{
 int i;
 char ch;
};

int main()
{
  FILE *stream;
  struct mystruct s,s1;
  clrscr();
  if ((stream = fopen("TEST.dat", "wb ")) == NULL) /* open file TEST.$$$ */
  {
     fprintf(stderr, "Cannot open output file.\n");
     return 1;
  }
  s.i = 0;
  s.ch = 'v';
  fwrite(&s, sizeof(s), 1, stream); /* write struct s to file */
  s1.i=11;
  s1.ch='R';
  fwrite(&s1, sizeof(s1), 1, stream);
  fclose(stream);
  stream = fopen("TEST.dat", "w b");
   rewind(stream);
  while(!feof(stream)){
  fread(&s, sizeof(sizeof( mystruct)), 1, stream);
  printf("\nstream %c",s.ch);
  };
  fclose(stream);
  getch(); /* close file */
  return 0;
}


Answer
Dear Mr Ben!

  Upon verifying your code i found lot of Bugs in your code ,
  
  >  stream = fopen("TEST.dat", "wb"); Opening again the file using wb mode will erase the contents of the file and open it as a new file so it should be avoided instead i have used "rb" mode.
  >  fread(&s, sizeof(sizeof( mystruct)), 1, stream); Now take a look at this statement siezof(sizeof(mystruct))  actually it should be like this sizeof(s) , its well enough

I had made some changes over your code , now its working pretty fine!


#include<stdio.h>
#include<conio.h>
struct mystruct
{
   int i;
   char ch;
};

int main()
{
 FILE *stream;
 struct mystruct s;
 clrscr();
 if ((stream = fopen("TEST.dat", "wb+ ")) == NULL) /* open file TEST.$$$ */
 {
    fprintf(stderr, "Cannot open output file.\n");
    return 1;
 }
 s.i = 0;
 s.ch = 'v';
 fwrite(&s, sizeof(s), 1, stream); /* write struct s to file */
 s.i = 1;
 s.ch = 'R';
 fwrite(&s, sizeof(s), 1, stream);
 fclose(stream);
 stream = fopen("TEST.dat", "rb+");
 rewind(stream);
 while(fread(&s, sizeof(s), 1, stream))
 {
  printf("\n %c %d",s.ch , s.i);
 }
 fclose(stream);
 getch();
 return 0;
}

Note:
  If you need any explanation over this code please dont hesitate to ask a follow up question

Thanks and Regards
Prince M. Premnath