Unix/Linux系統呼叫 » lseek()函式 Unix/Linux

lseek()函式 Unix/Linux

lseek - 重新讀取/寫入檔案偏移量

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 (’’) 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

本文件的使用那裡的是英文不正確，但維持歷史原因。

當與下面的巨集轉換舊的程式碼，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.

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