Regarding function pointer in C?

Question

I am beginner in C language and was learning about function pointer in C language. There I encountered a problem?

Write a compare function to sort by first character of name?

*int (firstnamecharcompar)(const void * a, const void * b))

Here is my code solution for this.

#include<stdlib.h>
#include<stdio.h>
#include <stdbool.h>

int compare1(const void *a,const void *b)
{
    char *c = *(char**)a;
    char *d = *(char**)b;
    return c[0] - d[0];
    //return ( *(char*)a[0] == *(char*)b[0] );
}

int main()
{
    char str[3][10];
    int i;
    for(i=0;i<3;i++)
    {
        printf("Enter %d string => " , i+1 );
        scanf("%s", str[i]);
        printf("\n");
    }
    
    for(i=0;i<3;i++)
    {
        printf("%s ",str[i]);
    }
    
    qsort(str,3,10,compare1);
    
    for(i=0;i<3;i++)
    {
        printf("%s ",str[i]);
    }
    return 0;
}

But my code is getting terminated without giving any output? What is problem with my code?

Answer 1

char *c = *(char**)a;
char *d = *(char**)b;

These lines would be valid if you were sorting an array of pointers to char. You are in fact sorting an array of 10-element char arrays. Adjust the casts accordingly:

char *c = *(char(*)[10])a;
char *d = *(char(*)[10])b;