Thread: Having trouble passing a value from a function

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


#define MAX_CMD_LINE 500


void chk_for_redirect(char *fun_tknzd,  char *opt_rdrct_2, char *inpt_rdrct_2);


int main(void)
{


        char *str_tknzd[MAX_CMD_LINE], *opt_rdrct = NULL, *inpt_rdrct = NULL, test[] = ">tester";

        str_tknzd[1] = test;

        // this function is returning NULL for opt_rdrct and I am not sure why
        // I think my problem is here
        chk_for_redirect(str_tknzd[1], opt_rdrct, inpt_rdrct);

        // this is how I know it is returning NULL
        printf("Output redirect out of function: %s\n", opt_rdrct);
        printf("Input redirect out of function: %s\n", inpt_rdrct);


         return 0;


}


void chk_for_redirect(char *fun_tknzd,  char *opt_rdrct_2, char *inpt_rdrct_2)
{
           if(strchr (fun_tknzd, '>') == fun_tknzd){
              opt_rdrct_2 = strchr (fun_tknzd, '>');
              printf("Output redirect: %s\n", opt_rdrct_2);
            }

            else if(strchr (fun_tknzd, '<') == fun_tknzd){
                inpt_rdrct_2 = strchr (fun_tknzd, '<');
                printf("Input redirect: %s\n", inpt_rdrct_2);
            }


}

The value that opt_rdrct_2 & inpt_rdrct_2 point to are not being passed to opt_rdrct and inpt_rdrct.

Thanks in advance for the help

Please, indent your code.

I also inform that you do not need to append _2 to the name of the argument. Arguments can have their very own names and it is ok to have the same name as another variable in main().

You have a char pointer and you want to modify it. How do you expect it to be modified, if you pass a char pointer? It's - pretty much - like the swap example (which I think you have been taught) . You should pass a pointer to what you want to modify. So you should pass a pointer to a char pointer, which is a double char pointer.

Moreover, notice that only of your arguments are going to be set to something different than NULL, because of the if-else statement.
Notice also, that actually, non of them might be modified, because the condition at the if and if else statements may result to false.

EDIT:

Code:

str_tknzd[1] = test;

You think that copies strings? No, strcpy does.

Sorry about the indentation. I was aware that the arguments can be the same, I just like to name them differently. I also was aware of the if else statement and that one of the arguments will be set to NULL. However in the above example I passed it a value. I set, str_tknzd[1] = test( this is an edit, I missed, "You think that copies strings? No, strcpy does.", I thought that it sets the pointer to the address of test.) This means that opt_rdrct_2 should be equal to test. As to your statement, "You should pass a pointer to what you want to modify. So you should pass a pointer to a char pointer, which is a double char pointer." I don't understand what you are saying. I have tried to pass the function the the pointers. I am afraid I am missing something you are trying to convey to me. Can you clarify? Thank you for your help.

I also checked your website for some additional information on passing pointers to function, but was unable to locate any material on the subject.