ftello64
—return position in a stream or file ¶Synopsis
#include <stdio.h> _off64_t ftello64(FILE *fp); _off64_t _ftello64_r(struct _reent *ptr, FILE *fp);
Description
Objects of type FILE
can have a “position” that records how much
of the file your program has already read. Many of the stdio
functions
depend on this position, and many change it as a side effect.
The result of ftello64
is the current position for a large file
identified by fp. If you record this result, you can later
use it with fseeko64
to return the file to this
position. The difference between ftello
and ftello64
is that
ftello
returns off_t
and ftello64
is designed to work
for large files (>2GB) and returns _off64_t
.
In the current implementation, ftello64
simply uses a character
count to represent the file position; this is the same number that
would be recorded by fgetpos64
.
The function exists only if the __LARGE64_FILES flag is defined.
An error occurs if the fp was not opened via fopen64
.
Returns
ftello64
returns the file position, if possible. If it cannot do
this, it returns -1
. Failure occurs on streams that do not support
positioning or not opened via fopen64
; the global errno
indicates
this condition with the value ESPIPE
.
Portability
ftello64
is a glibc extension.
No supporting OS subroutines are required.