Are char * argv[] arguments in main null terminated?

c argv null-terminated
LeviX picture LeviX · Jun 13, 2012 · Viewed 23.5k times · Source

So I'm wondering if command line parameters are always null terminated? Google seems to say yes, and compiling on GCC indicates this is the case, but can I guarantee this to always be true?

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

    for(int cnt=1; cnt < argc; ++cnt)
    {
        p = argv[cnt];
        printf("%d = [%s]\n", cnt, p);
    }
    return 0;
}

$ MyProgram -arg1 -arg2 -arg3
1 = -arg1
2 = -arg2
3 = -arg3

Answer

James McNellis picture James McNellis · Jun 13, 2012

Yes. The non-null pointers in the argv array point to C strings, which are by definition null terminated.

The C Language Standard simply states that the array members "shall contain pointers to strings" (C99 §5.1.2.2.1/2). A string is "a contiguous sequence of characters terminated by and including the first null character" (C99 §7.1.1/1), that is, they are null terminated by definition.

Further, the array element at argv[argc] is a null pointer, so the array itself is also, in a sense, "null terminated."

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