lseek - 重新讀取/寫入文件偏移量

內容簡介

#include <sys/types.h> 
#include <unistd.h>

off_t lseek(int fildes, off_t offset, int whence);

描述

The lseek() function repositions the offset of the open file associated with the file descriptor fildes to the argument offset according to the directive whence as follows:

標簽	描述
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 file (but this does not change the size of the file). If data is later written at this yiibai, subsequent reads of the data in the gap (a "hole") return null bytes (’\0’) until data is actually written into the gap.

返回值

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 errnois set to indicate the error.

錯誤

標簽	描述
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, or beyond the end of a seekable device.
EOVERFLOW
	The resulting file offset cannot be represented in an off_t.
ESPIPE	fildes is associated with a pipe, socket, or FIFO.

遵循於

SVr4, 4.3BSD, POSIX.1-2001.

RESTRICTIONS

Some devices are incapable of seeking and POSIX does not specify which devices must support lseek().

Linux specific restrictions: using lseek() on a tty device returns ESPIPE.

注意

本文檔的使用那裡的是英文不正確，但維持曆史原因。

當與下麵的宏轉換舊的代碼，用於何處替換值：

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 yiibaier, so seeking on such files may be subject to race conditions.

另請參閱

• dup (2)

• fork (2)

• open (2)