fwrite

ftell

#include <stdio.h>long int ftell(FILE *stream);

The ftell( ) function returns the current value of the file position indicator for the specified stream. In the case of binary streams, the value is the number of bytes the indicator is from the beginning of the file. For text streams, the return value may not be meaningful except as an argument to fseek( ) because of possible character translations, such as carriage return/linefeeds being substituted for newlines, which affect the apparent size of the file.

The ftell( ) function returns –1 when an error occurs.

Related functions are fseek( ) and fgetpos( ).