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cglibc

A variable declaration following an argument list

Reading glibc, I saw this piece of code in string/strerror.c:

char *
strerror (errnum)
     int errnum;
{
  char *ret = __strerror_r (errnum, NULL, 0);
  int saved_errno;

  if (__glibc_likely (ret != NULL))
    return ret;
  saved_errno = errno;
  if (buf == NULL)
    buf = malloc (1024);
  __set_errno (saved_errno);
  if (buf == NULL)
    return _("Unknown error");
  return __strerror_r (errnum, buf, 1024);
}

Note how there is a int errnum following the argument list. How is this a valid syntax? And what is it doing?

Solution

  • That's the old-style way of doing things, K&R, pre-ANSI.

    Once function prototypes were introduced, this way of doing things was rendered obsolete.

    Not actually obsolete since it's still valid even in C11 (as per 6.9.1 Function definitions /13), but few people use it any more).

    It's specifying the type of the parameter for the function block, similar to:

    char *strerror (int errnum)