read an empty file with fread

Question

I am trying to read an empty file with fread. Before i created the file with a blocksize of 4096 and an amount of 40 blocks. At the moment I know that these Blocks are "empty" but if i read the file like in my code below I cannot tell wether it is empty or not. I mean I am expecting nread to be NULL or something like that. Do you know what I have to compare nread with? Thank you!

int test()
{

   char buf[4096];
   FILE *file;
   size_t nread;

   file = fopen("out/abc.store", "r");
   if (file) {
       while ((nread = fread(buf, 1, sizeof buf, file)) > 0)
          fwrite(buf, 1, nread, stdout);
      if (ferror(file)) {
      /*error handling*/
   }
   fclose(file);
}

EDIT:

I created the file like that:

char *content=(char*)malloc(uintBlockSize*uintBlockCount);
memset(content,0,uintBlockSize*uintBlockCount);
...
 while (i!=0)
 {
   check=fwrite(content,uintBlockSize, 1, storeFile);
   if (check!=1)
       return 1;
   i--;
 }

If you created the file with a size greater than zero, it is not empty. — Carey Gregory, Aug 15 '13 at 14:57
[Please don't cast the return value of `malloc()` in C](http://stackoverflow.com/a/605858/28169). — unwind, Aug 15 '13 at 15:05
Please don't vandalized your questions. If you want it deleted flag but give a *good* reason. — Flexo, Aug 15 '13 at 18:24

score 1 · Answer 1 · answered Aug 15 '13 at 14:56

1

Check to see if fread returned 0. From the documentation (here):

The total number of elements successfully read is returned.

answered Aug 15 '13 at 14:56

Jacob Pollack

3,703
1
17
39

:S i think i made a mistake with my question the file is not empty. But i created it like i wrote it in the edit. – SevenOfNine Aug 15 '13 at 15:02
It will not return zero. It will return 4096 and it will do so 40 times. – Carey Gregory Aug 15 '13 at 15:03
i am sorry can i delete this question somehow? – SevenOfNine Aug 15 '13 at 15:05
@user2430568 - Yes, you can delete your own questions. Or you can edit it to clarify your question. – Carey Gregory Aug 15 '13 at 15:07
so how can i delete it? – SevenOfNine Aug 15 '13 at 15:07

score -1 · Answer 2 · answered Aug 15 '13 at 14:59

-1

fread will return the number of successfully read elements, so in this case, fread will return 0 (assuming it did not read anything), or EOF if it is the end.

answered Aug 15 '13 at 14:59

phyrrus9

1,441
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read an empty file with fread

2 Answers2