unsigned char open (FCB *fcb, const char *fn);

Open an existing file for reading or writing.

fcb =Pointer to file control block.
fn =Pointer to file name. If NULL the FCB is assumed to contain a file name.
Return:0 - OK. 1 - Invalid drive. 2 - Name too long. 3 - Extension too long. 4 - Open failed.

Include file: diskio.h