C fopen()

#include <stdio.h>
FILE *fopen(const char *restrict filename, const char *restrict mode);


mode is listed as following:

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

reference from http://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html