Thread: String swap - function

Hi I'm new here and I would like some help because my code produces a run time error.
My problem is I'm going to create a function called reverse_string of type void with a char pointer as an argument called str.
My program compiles fine. Any feedback would be helpful. Thank you

Code:

void reverse_string(char *str)
{
    int ctr = 0, tctr = 0;
    char temp;

    while(str[tctr] != '\0'){ tctr++; }

    while(ctr < tctr)
    {
        temp = str[ctr]; // swap characters
        str[ctr] = str[tctr - 1]; 
        str[tctr - 1] = temp;
         ctr++;
         tctr--;
     }
}

Your algorithm is implemented correctly. The runtime error is caused by an other instruction. Maybe you are trying to reverse a string which is a constant literal? You need show the rest of the code.

Hi DRK,
Thanks for the fast reply.

The rest of my code is only this:

Code:

 
#include <stdio.h>

void main (void) 
{
    char *str = "hello" ;
    reverse_string(str) ;
    printf("reversed:%s\n", str) ;
}

Thank you DRK and WoodSTokk!
I have googled constant string literals and I found out that this code

Code:

 
char *str = "hello" ;

is indeed a constant and it cannot be modified.

The code that WoodSTokk suggested was indeed the solution. I have learned something new today.
Thank you so much for the quick replies.

Originally Posted by vart

to avoid such failures I prefer to define pointers to char literals as const

Code:

const char* str = "hello" ;

In this case compiler will give me a compilation error as soon I try to pass such var to the function which expects char*

Noted. Thank you so much