fopen , fwrite

fopen

r or rb

Open file for reading.

w or wb

Truncate to zero length or create file for writing.

a or ab

Append; open or create file for writing at end-of-file.

r+ or rb+ or r+b

Open file for update (reading and writing).

w+ or wb+ or w+b

Truncate to zero length or create file for update.

a+ or ab+ or a+b

Append; open or create file for update, writing at end-of-file.

fwrite:

size_t fwrite ( const void * ptr, size_t size, size_t count, FILE * stream );

int fseek(FILE *stream, long offset, int whence)

sets the file position indicator for the stream pointed to by stream

If whence is set to SEEK_SET, SEEK_CUR, or SEEK_END, the offset is relative to the start of the file, the current position indicator, or end-of-file, respectively

long ftell(FILE *stream)

obtains the current value of the file position indicator for the stream pointed to by stream.