getpwuid doesn't set errno

    uid_t userId = getuid();
    userId = 999;               // cause error

    errno = 0;
    passwd* pw = getpwuid(userId);

    int n = errno;    // pw = NULL, n = 0

Runn开发者_开发技巧ing this code in Linux, I get pw = NULL (expected), and errno = 0. According to Linux documentation http://linuxmanpages.com/man3/getpwuid.3.php, getpwuid must set errno. What is wrong?

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From the documentation:

ERRORS
         0 or ENOENT or ESRCH or EBADF or EPERM or ...
                The given name or uid was not found.

I fail to see a problem.

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According to the documentation you linked:

   0 or ENOENT or ESRCH or EBADF or EPERM or ...
          The given name or uid was not found.

So errno == 0 is perfectly valid for a uid not found.