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:

標籤

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  errno is set to indicate the error.

錯誤

標籤

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

本文檔的使用那裏的是英文不正確，但維持歷史原因。

當與下面的宏轉換舊的代碼，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)