Unix_Linux 的 dup

dup, dup2 - 復制一個文件描述符

內容簡介

#include int dup(int oldfd);

int dup2(int oldfd, int newfd);

描述

dup() 和?dup2() 創建文件描述符的副本?oldfd.

After a successful return from?dup() or?dup2(),the old and new file descriptors may be used interchangeably. They refer to the same open file description (see?open(2)) and thus share file offset and file status flags; for example, if the file offset is modified by using?lseek(2) on one of the descriptors, the offset is also changed for the other.

The two descriptors do not share file descriptor flags (the close-on-exec flag). The close-on-exec flag (FD_CLOEXEC; see?fcntl(2)) for the duplicate descriptor is off.

dup() 使用編號最小的未用描述符的新的描述符。

dup2()?使得newfd是oldfd副本，先關閉newfd，如果必要的話。

返回值

dup() anddup2() return the new descriptor, or -1 if an error occurred (in which case,errnois set appropriately).

錯誤

標簽

描述

EBADF

oldfd?isn’t an open file descriptor, or?newfd?is out of the allowed range for file descriptors.

EBUSY

(Linux only) This may be returned by?dup2() during a race condition with?open() and?dup().

EINTR

The?dup2() call was interrupted by a signal.

EMFILE

The process already has the maximum number of file descriptors open and tried to open a new one.

警告

The error returned by?dup2() is different from that returned by?fcntl(...,?F_DUPFD, ...)when?newfd?is out of range. On some systems?dup2() also sometimes returns?EINVALlike?F_DUPFD.

If?newfd?was open, any errors that would have been reported at?close() time, are lost. A careful programmer will not use?dup2() without closing?newfd?first.

遵循于

SVr4, 4.3BSD, POSIX.1-2001.

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