struct_sorting_example.c

/***************************************************************************
Sort a struct array in C using qsort function
****************************************************************************/

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

struct Student  { 
    char name[30]; 
    int id;
    int age;
};

//int ( * comparator ) ( const void *, const void * )
int comp_by_age(const void *a, const void * b)
{
    struct Student *s1 = (struct Student *) a;
    struct Student *s2 = (struct Student *) b;
    
    return (int) (s1->age - s2->age); // ascending order by age
    // return (int) (s1->age - s2->age); // descending order by age
}

int main()
{
    struct Student a[3];

    // Student 1 
    strcpy(a[0].name, "Mehadi"); 
    a[0].id = 10; 
    a[0].age = 25 ; 

    // Student 2
    strcpy(a[1].name, "Hasan"); 
    a[1].id = 5; 
    a[1].age = 24 ; 

    // Student 3
    strcpy(a[2].name, "Menon"); 
    a[2].id = 100; 
    a[2].age = 30 ; 

    printf("%s\n", a[0].name);
    printf("%s\n", a[1].name);
    printf("%s\n", a[2].name);
    
    
    //void qsort (void * base, size_t num, size_t size, int (* comparator) (const void *, const void * ));
    
    qsort(a, 3, sizeof(struct Student), comp_by_age);
    
    printf("\nAfter Sorting: \n");
    printf("%s\n", a[0].name);
    printf("%s\n", a[1].name);
    printf("%s\n", a[2].name);

    return 0;
}