Thread: Help with reverse string in recursion

having trouble with reversing a string using recursion, i want my function to take 1 parameter which is a pointer to the string and reverse it recursively,if possible.
here is what i have now:

Code:

void rev(char *str){
char t;
char *s=str;//point to the first character
char *e=str+(strlen(str)-1);//point to the last character
if(s>e)
{
return;
}
rev(str++);/*<---here is my problem,now the last character will be the same one after the first call and i dont want that i want it to be the character before the last and so on,any ideas?*/
t=*s;
*s=*e;
*e=t;
}

Originally Posted by Stark88

i have solved it like this by adding a static variable but i don't like it,if you have any ideas i would be grateful.

You are right to dislike the use of a static variable. A better idea is to make use of a helper function:

Code:

static void rev_helper(char *str, size_t len) {
    if (len > 1) {
        /* swap and do the recursive call
           ...
         */
    }
}

void rev(char *str) {
    rev_helper(str, strlen(str));
}

Note that you do not need to call strlen in rev_helper because the current string length is already known via the parameter. Additionally, I declared the helper function static since it is implementation detail purely to assist the implementation of rev: you certainly would not declare it in a header file.