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Manuál Linux
[Linux manuál]

lseek: přemístění souboru pro čtení / zápis

Originální popis anglicky: lseek - reposition read/write file offset

Návod, kniha: Linux Programmer's Manual

STRUČNĚ

#include <sys/types.h>
 
#include <unistd.h>
 
off_t lseek(int fildes, off_t offset, int whence);

POPIS / INSTRUKCE

The lseek function repositions the offset of the file descriptor fildes to the argument offset according to the directive whence as follows:
SEEK_SET
The offset is set to offset bytes.
SEEK_CUR
The offset is set to its current location plus offset bytes.
SEEK_END
The offset is set to the size of the file plus offset bytes.
The lseek function allows the file offset to be set beyond the end of the existing end-of-file of the file (but this does not change the size of the file). If data is later written at this point, subsequent reads of the data in the gap return bytes of zeros (until data is actually written into the gap).

NÁVRATOVÁ HODNOTA

Upon successful completion, lseek returns the resulting offset location as measured in bytes from the beginning of the file. Otherwise, a value of (off_t)-1 is returned and errno is set to indicate the error.

CHYBY / ERRORY

EBADF
fildes is not an open file descriptor.
EINVAL
whence is not one of SEEK_SET, SEEK_CUR, SEEK_END, or the resulting file offset would be negative.
EOVERFLOW
The resulting file offset cannot be represented in an off_t.
ESPIPE
fildes is associated with a pipe, socket, or FIFO.

ODPOVÍDAJÍCÍ

SVr4, POSIX, BSD 4.3

RESTRICTIONS

Some devices are incapable of seeking and POSIX does not specify which devices must support it.
 
Linux specific restrictions: using lseek on a tty device returns ESPIPE.

NOTES

This document's use of whence is incorrect English, but maintained for historical reasons.
 
When converting old code, substitute values for whence with the following macros:
old new
0 SEEK_SET
1 SEEK_CUR
2 SEEK_END
L_SET SEEK_SET
L_INCR SEEK_CUR
L_XTND SEEK_END
SVR1-3 returns long instead of off_t, BSD returns int.
Note that file descriptors created by dup(2) or fork(2) share the current file position pointer, so seeking on such files may be subject to race conditions.

SOUVISEJÍCÍ

dup(2), fork(2), open(2), fseek(3)
2001-09-24 Linux
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