c - 如何使用C中的sort函数按升序对字符串数组进行排序

Question

假设我有一个名为字典的结构，其中包含两个字符数组。我想根据第二个字符数组升序对字典类型数组“对”进行排序。如何使用排序功能做到这一点？我需要如何修改comp？

Answer 1

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

typedef struct
{
    unsigned char message[100];   // string to be sorted
                                  // (totally arbitrary length)
    unsigned char sortOrder[256]; // string containing ASCII chars
                                  // in their sort order
} Pair;

unsigned char rank[256]; // rank of each ASCII character

// qsort() comparison function
int sortByRank(const void *a, const void *b)
{
    return ((int)rank[*(signed char *)a] - (int)rank[*(signed char *)b]);
}

// Creates an array by which a character's relative position can be found
// solely from its value.  Characters of rank 0 will appear first when sorted.
// Characters not specified by sortOrder will appear first, since rank is
// global and automatically initialized to zeros.
void initRank(Pair pair)
{
    int i;

    for (i = 0; i < strlen(pair.sortOrder); i++)
        rank[pair.sortOrder[i]] = i;

    return;
}

int main()
{
    // Create an example pair.  Spaces will be the first characters in the
    // sorted result.
    Pair pair;
    strcpy(pair.message, "this is a test message (123).");
    strcpy(pair.sortOrder, " 321abcdefghijklm.nopqrstuvwxyz()");

    // In this solution, initRank() will need to be called any time the
    // sortOrder is changed.
    initRank(pair); 

    // Sort using the global rank array set by initRank()
    qsort(pair.message, strlen(pair.message), sizeof(char), sortByRank);

    printf("Sorted message: %s\n", pair.message);

    // Output:
    // Sorted message:      321aaeeeghiim.sssssttt()

    return 0;
}

由于 rank[] 是全局的，这并不像可能的那么优雅，但上述解决方案通常演示了如何利用 C 的排序函数以相当简单的方式基于第二个字符串进行自定义排序。