c - argv[argc] 是否等于 NULL 指针

Question

我读了一篇文章（忘记了网址），上面说argv[argc]是一个NULL指针（包含\0）。为了检查它是否是真的，我写了这段代码，是的，它存在。我不明白的是，为什么操作系统NULL在argv[argc]. 它对其他东西也有用吗？

int
main (int argc, char **argv){

    while (*argv)
        printf ("%s\n", *argv++);

    return 0;
}

Answer 1

The C Standard 5.1.2.2.1/2 second mark says explicitly

argv[argc] shall be a null pointer.

The C++ Standard 3.6.1/2 also says explicitly

The value of argv[argc] shall be 0.

Answer 2

The Standard (C99 5.1.2.2.1p2) mandates that:

If they are declared, the parameters to the main function shall obey the following constraints:

— The value of argc shall be nonnegative.

— argv[argc] shall be a null pointer.

...

The rationale for this is to provide a redundant check for the end of the argument list, on the basis of common practice (ref: Rationale for the ANSI C programming language (1990), 2.1.2.2).