CODEWITHSUNDEEP
cfwrite
Itsik Elia
Itsik Elia

Reputation: 63

c language : fwrite doesnt do anything

{
    FILE* f1 = fopen("C:\\num1.bin", "wb+");//it will create a new file 
    int A[] = { 1,3,6,28 }; //int arr
    fwrite(A, sizeof(A), 1, f1); //should insert the A array to the file
}

I do see the file but even after the fwrite, the file remains empty (0 bytes), does anyone know why?

Upvotes: 3

Views: 1339

Answers (3)

Govind Parmar
Govind Parmar

Reputation: 21542

A couple of things:

  1. As @Grantly correctly noted above, you are missing a call to fclose or fflush after writing to the file. Without this any cached/pending writes will not necessarily be actually written to the open file.
  2. You do not check the return value of fopen. If fopen fails for any reason it will return a NULL pointer and not a valid file pointer. Since you're writing directly to the root of the drive C:\ on a Windows platform, that's something you definitely do want to be checking for (not that you shouldn't in other cases too, but run under a regular user account that location is often write protected).

Upvotes: 5

Mateusz Grzejek
Mateusz Grzejek

Reputation: 12058

Result of fwrite is not required to appear in the fille immediately after it returns. That is because file operations usually work in a buffered manner, i.e. they are cached and then flushed to speed things up and improve the performance.

The content of the file will be updated after you call fclose:

fclose()

(...) Any unwritten buffered data are flushed to the OS. Any unread buffered data are discarded.

You may also explicitly flush the internal buffer without closing the file using fflush:

fflush()

For output streams (and for update streams on which the last operation was output), writes any unwritten data from the stream's buffer to the associated output device.

Upvotes: 2

Grantly
Grantly

Reputation: 2556

You need to close the file with fclose

Otherwise the write buffer will not (necessarily) force the file contents to be written to disk

Upvotes: 7

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