C reading binary files

> **Possible Duplicate:**
> [ “while( !feof( file ) )” is always wrong](

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If I write an array to the output file and I close the file, then open the file again and read everything until end-of-file is reached, although the file contains only 4 number, the program will read and print 5 numbers, why?

Program output:

a[0] = 4
a[1] = 7
a[2] = 12
a[3] = 34
a[4] = 34

save.bin (with a hex editor)

04000000 07000000 0C000000 22000000

------

#include <stdio.h>
#include <stdlib.h>
#define path "save.bin"

int main(void)
{
FILE *f=NULL;
int a[]={4,7,12,34},i,n=4,k;
f=fopen(path,"wb");
if(f==NULL)
{
perror("Error");
exit(1);
}
for(i=0;i<n;i++) // or I could use fwrite(a,sizeof(int),n,f);
fwrite(&a[i],sizeof(int),1,f);
fclose(f);
f=fopen(path,"rb");
if(f==NULL)
{
perror("Error");
exit(1);
}
i=0;
while(!feof(f))
{
fread(&k,sizeof(int),1,f);
printf("a[%d] = %d\n",i,k);
i++;
}
printf("\n");
fclose(f);
return 0;
}

while(!feof(f))
{
fread(&k,sizeof(int),1,f);
printf("a[%d] = %d\n",i,k); /** THIS ASSUMES fread() WAS SUCCESSFUL. **/
i++;
}

Check for end of file immedately after the call to `fread()` or check the return value of `fread()`, which returns the number of items read which in this case should be `1`. A possible restructuring of the loop:

while(1 == fread(&k,sizeof(int),1,f))
{
printf("a[%d] = %d\n",i,k);
i++;
}

After the loop check `feof()` to ensure EOF was reached and loop did not end due to some other failure.

I have the same problem as well. Try this instead:

i=0;
while(true)
{
fread(&k,sizeof(int),1,f);
if(feof(f))
break;

printf("a[%d] = %d\n",i,k);
i++;
}

Apparently feof doesnt return true unless you've read past the end of the file. What i do when writing arrays to binary files is to write the size first, so i know the exact amount of data i'm about to read when reading it back.

`feof(fp)` becomes false (i.e. non-zero value) only if you tried to *read past* the end of file. That should explain why the loop is entered one more than what you expect.


From the [documentation][1]:

The function feof() tests the end-of-file indicator for the stream
pointed to by stream, returning nonzero if it is set. The end-of-
file indicator can be cleared only by the function clearerr().

[1]:

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