Question

I have written this simple program to print a string in reverse order but it is showing segmentation fault.

#include<stdio.h>
#include<string.h>
int main (int argc, char **argv)
{
        char *string;
        int n;
        printf("Enter a string\n");
        scanf("%s",string);
        printf("\n");
        n = strlen(string);
        printf("%d",n);
        while(n != 0)
        {
                printf("%c",string[n]);
                n--;
        }
        return(0);
}

Can anybody explain me why I am getting this segmentation fault? Opearating system : Ubuntu , compilor : gcc

Answer 1

char *string creates a variable which can hold a pointer to a string, but it is not set here. So it points to a random location which, when accessed, segfaults.

To be useful, either allocate some memory and assign that to the pointer:

char *string = malloc(1000);  // big enough for string

or, do it all at once:

char string[1000];

Ideally, instead of using a hardcoded constant (like my example 1000) use a symbolic constant, or better yet, find out how long the string needs to be and then use that.