Question

I have been working through Stroustrup’s C++ programming language, and I am having difficulties with an early exersize. The task is to build a method rev that reverses a c style string. I think my logic is right, but I get an error when I try to modify the string. Can I not do this?

int strlen_(char* string)
{
    int count = 0;
    while (*string != '\0'){
        count ++;
        string ++;
    }

    return count;
}

void rev(char* string)
{
    //length of the string is going to be useful 
    int len = strlen_(string);

    //two counters, one going forward, one going back

    int forwardIndex = 0;
    int backwardIndex = len-1; 

    char temp;
    while (forwardIndex < backwardIndex){
        temp = string[forwardIndex];
        string[forwardIndex] = string[backwardIndex];   //Exception Here
        string[backwardIndex] = temp;
        forwardIndex--;
        backwardIndex--;
    }

}

void main()
{
    char* test = "test"; 
    rev(test);
}

Answer 1

You can’t modify literal strings, and your reverse function modifies it’s string argument.

Test your reverse function by passing something like this instead:

void main()
{
    char test[] = "test";
    rev(test);
}

This will make a copy of the literal string "test" in an array that you can modify.

Also, you’re decrementing both forwardIndex and backwardIndex: you should be incrementing forwardIndex: forwardIndex++. The idea is that the indices will meet in the middle.