CODEWITHSUNDEEP
c
pippo inzaghi
pippo inzaghi

Reputation: 33

Array of strings. Compiler error. Maybe memory out of bounds?

I am trying to understand the concept of array of char pointers in C. In this basic example I try to get the number of strings using the x++ operator but, unfortunately I get a compiler error because maybe I try to access an extra region of memory but I shoudn't? Thanks for any help.

#include <stdio.h>

int main()
{
    char *argv[]= {"hello","world"};
    int num = 0;

    while (argv[num++] != NULL){
        printf("num value: %i\t  %c\n",num,*argv[num-1]);
    }

    printf("Final num value: %i\n",num);

    return 0;
}

Upvotes: 1

Views: 65

Answers (1)

Stephan Lechner
Stephan Lechner

Reputation: 35154

You are exceeding array bounds since

 while (argv[num++] != NULL)

will stop when argv[num] is NULL, yet argv[]'s dimension is 2, and both entries are != NULL.

You could write...

 char *argv[]= {"hello","world",NULL};

and it should work with your end condition as is.

BTW: you are aware that argv[] is often used as name for the parameters to function main, i.e. int main(int argc, char* argv[]), which represent the command line arguments when your program gets called, are you? When you use the function main-parameter, I think that the last valid element of it will by NULL by definition (cf., for example, this online C11 standard draft):

5.1.2.2.1 Program startup

....

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

argv[argc] shall be a null pointer.

If you create your "own" local argv[]-thing, however, you have to do this explicitly on your own.

Upvotes: 6

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