argc and argv in C

Question

Suppose I have this example function

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

        char* pChar = argv[2]; // Get the second argument "Word"
        char * pAdd = pChar + strlen(pChar); // 0 + 5
}

and run by inputting ./fileName Hello World

Since argv[2] = World, pChar should point to the memory address of the Char "World"

However, what I don't get is why pChar = 0 (that is what the book says) when executing pChar + strlen(pChar) line of code.

*However, what I don't get is why pChar = 0 when executing pChar + strlen(pChar) line of code.* How do you know `pChar` is `0`? — Andrew Henle, Oct 16 '18 at 10:44
Because the string is just "World" and C strings are terminated by a 0. What did you expect it to be? — Rup, Oct 16 '18 at 10:46
"the book" - what book? Run the code, see for yourself. The book either has a typo, or you are misreporting what it says. — Clifford, Oct 16 '18 at 10:58

Gaurav · Answer 1 · 2018-10-16T10:58:58.827

2

pChar is not 0.

POSSIBLE ERROR: *pAdd is 0 instead of pChar since pAdd is pointing to the last character of string "World" i.e. '\0' and integral value of null termination ('\0') is 0.

You want to say that address is 0 - you might need to read about that:

in c can an address of a pointer be 0

edited Oct 16 '18 at 10:58

answered Oct 16 '18 at 10:51

Gaurav

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score 1 · Answer 2 · answered Oct 16 '18 at 10:55

You need to explain or demonstrate how you made the observation. pChar will not be zero, however it will point to the NUL character at the end of the second argument. i.e *pChar will be NUL - demonstrated by the empty string pointed to by pAdd here:

The upshot is, make your observations using a debugger - it is the least intrusive method and does not rely on you writing debug code correctly.

argc and argv in C

2 Answers2