sort_array_of_structures.c

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

typedef struct{
    int id;
    char name[20];
} dict;

int intcmp(const void *a, const void *b){
    return ((dict *)a)->id - ((dict *)b)->id;
}

int intrcmp(const void *a, const void *b){
    return ((dict *)b)->id - ((dict *)a)->id;
}

int stringcmp(const void *a, const void *b){
    return strcmp(((dict *)a)->name, ((dict *)b)->name);
}

int stringrcmp(const void *a, const void *b){
    return strcmp(((dict *)b)->name, ((dict *)a)->name);
}

void output(dict *data){
    int i;
    for(i=0; i<3; i++)
        printf("%3d %s\n", data[i].id, data[i].name);
}

int main(void){
    dict data[3] = {{1, "Alice"}, {3, "Bob"}, {2, "Chris"}};

    puts("ID降順");
    qsort(data, 3, sizeof(dict), intrcmp);
    output(data);

    puts("ID昇順");
    qsort(data, 3, sizeof(dict), intcmp);
    output(data);

    puts("名前降順");
    qsort(data, 3, sizeof(dict), stringrcmp);
    output(data);

    puts("名前昇順");
    qsort(data, 3, sizeof(dict), stringcmp);
    output(data);

    return 0;
}