从写（2）在C返回值为0的错误？ [英] Is a return value of 0 from write(2) in C an error?

问题描述

在为系统调用写手册页（2） -

In the man page for the system call write(2) -

ssize_t供写入（INT FD，常量无效* buf中，为size_t计数）;

它说以下内容：

返回值

在成功，字节数
  书面返回（零表示
  没有写）。错误时，-1
  回来了，错误号设置
  适当。如果计数为零，并
  文件描述符是指一种
  常规文件，0可以返回，或
  可检测到的错误。对于一个特殊的
  文件时，该结果不是便携式的。

On success, the number of bytes written are returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately. If count is zero and the file descriptor refers to a regular file, 0 may be returned, or an error could be detected. For a special file, the results are not portable.

我会间preT这意味着返回0，简单的说就是没有写，无论出于何种原因，随心所欲。

I would interpret this to mean that returning 0 simply means that nothing was written, for whatever arbitrary reason.

不过，史蒂文斯在与UNP这是一个TCP套接字文件描述符打交道时对待的返回值为0，作为一个致命错误（这是由它调用退出（另一个功能包1）在短期计数）：

However, Stevens in UNP treats a return value of 0 as a fatal error when dealing with a file descriptor that is a TCP socket ( this is wrapped by another function which calls exit(1) on a short count ):

ssize_t /* Write "n" bytes to a descriptor. */
writen(int fd, const void *vptr, size_t n)
{
    size_t      nleft;
    ssize_t     nwritten;
    const char  *ptr;

    ptr = vptr;
    nleft = n;
    while (nleft > 0) {
        if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
            if (nwritten < 0 && errno == EINTR)
                nwritten = 0;       /* and call write() again */
            else
                return(-1);         /* error */
        }

        nleft -= nwritten;
        ptr   += nwritten;
    }
    return(n);
}

他只把0作为一个合法的返回值，如果错误号表示调用write是由该方法接收信号中断。

He only treats 0 as a legit return value if the errno indicates that the call to write was interrupted by the process receiving a signal.

为什么？

推荐答案

史蒂文斯或许这是否赶上老的实现
写（）的表现不同。例如，单一Unix规格
说（ http://www.opengroup.org/onlinepubs/ 000095399 /功能/ write.html ）

Stevens probably does this to catch old implementations of write() that behaved differently. For instance, the Single Unix Spec says (http://www.opengroup.org/onlinepubs/000095399/functions/write.html)

如果此卷IEEE标准
  1003.1-2001要求-1被返回，并errno设置为[EAGAIN]，最
  历史实现返回零

Where this volume of IEEE Std 1003.1-2001 requires -1 to be returned and errno set to [EAGAIN], most historical implementations return zero

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