The following code should be run in Linux and the harddisk or disk partition has no much space.
Code:
  $fp = fopen("abc.txt","w");
  fwrite($fp,"abcdefg");
  fclose($fp);

After running the code, the file "abc.txt" is created but with 0 bytes.(No content in the file). The fwrite function should return 0 if it cannot write anything on the file.