13.12. fgetpos(), fsetpos()

Get the current position in a file, or set the current position in a file. Just like ftell() and fseek() for most systems.

Prototypes

#include <stdio.h>

int fgetpos(FILE *stream, fpos_t *pos);
int fsetpos(FILE *stream, fpos_t *pos);

Description

These functions are just like ftell() and fseek(), except instead of counting in bytes, they use an opaque data structure to hold positional information about the file. (Opaque, in this case, means you're not supposed to know what the data type is made up of.)

On virtually every system (and certainly every system that I know of), people don't use these functions, using ftell() and fseek() instead. These functions exist just in case your system can't remember file positions as a simple byte offset.

Since the pos variable is opaque, you have to assign to it using the fgetpos() call itself. Then you save the value for later and use it to reset the position using fsetpos().

Return Value

Both functions return zero on success, and -1 on error.

Example

char s[100];
fpos_t pos;

fgets(s, sizeof(s), fp); // read a line from the file

fgetpos(fp, &pos);   // save the position

fgets(s, sizeof(s), fp); // read another line from the file

fsetpos(fp, &pos);   // now restore the position to where we saved

See Also

fseek(), ftell(), rewind()