segmentation fault when swapping pointer values while reversing a string [duplicate]

Question

I am trying to reverse a string. I take two pointers , one pointing to the start of the string and other at the end of the string . And then I swap the values of the pointers.

int main()
{

    char *string = "stack overflow";
    int len = strlen(string);
    char *end;
    char tmp; //temporary variable to swap values

    //pointer pointing at the end of the string
    end = string+len-1;

    printf(" value of start and end %c %c", *string , *end); //correct values printed
    while(string<end)
        {

                tmp = *string;
                *string = *end; //segmentation fault
                *end = tmp;
                *string++;
                *end--;


        }


    return 0;

}

you can't modify a string constant, use char string[] = "stack overflow" instead — Stephen Lin
– Stephen Lin, Commented Mar 12, 2013 at 23:56
You are not swapping pointer values. You are swapping values pointed by those pointers. Anyway, this has been asked hundreds of times already Why is this C code causing a segmentation fault? — AnT stands with Russia
– AnT stands with Russia, Commented Mar 12, 2013 at 23:57

user529758 · Accepted Answer · 2013-03-12 23:56:15Z

5

char *string = "stack overflow";

This creates a read-only string literal. Modifying it is undefined behavior. Use an array instead:

char string[] = "stack overflow";

answered Mar 12, 2013 at 23:56

user529758

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