我正在嘗試使用 qsort 函式對指向結構的指標陣列進行排序，代碼如下：
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct hotel {
char *address;
_Bool full;
int nrooms;
};
/* compare based on the value of nrooms */
int roomcomp(const void *p1, const void *p2)
{
return (
((struct hotel *)p1)->nrooms -
((struct hotel *)p2)->nrooms
);
}
/* compare based on the alphabetic value of address */
int addcomp(const void *p1, const void *p2)
{
return strcmp(
((struct hotel *)p1)->address,
((struct hotel *)p2)->address
);
}
int main()
{
struct hotel *p1 = malloc(sizeof(struct hotel));
struct hotel *p2 = malloc(sizeof(struct hotel));
struct hotel *p3 = malloc(sizeof(struct hotel));
struct hotel *p4 = malloc(sizeof(struct hotel));
p1->address = strdup("aaaa");
p1->nrooms = 100;
p2->address = strdup("bbbb");
p2->nrooms = 200;
p3->address = strdup("cccc");
p3->nrooms = 300;
p4->address = strdup("dddd");
p4->nrooms = 400;
struct hotel *arr[] = {p1, p2, p3, p4};
size_t size = sizeof(arr) / sizeof(*arr);
for (int i = 0; i < size; i ) {
printf("address: %s - nrooms: %d\n", arr[i]->address, arr[i]->nrooms);
}
putchar('\n');
qsort(arr, size, sizeof(struct hotel *), roomcomp);
for (int i = 0; i < size; i ) {
printf("address: %s - nrooms: %d\n", arr[i]->address, arr[i]->nrooms);
}
}
這是我得到的結果：
address: aaaa - nrooms: 100
address: bbbb - nrooms: 200
address: cccc - nrooms: 300
address: dddd - nrooms: 400
address: aaaa - nrooms: 100
address: cccc - nrooms: 300
address: dddd - nrooms: 400
address: bbbb - nrooms: 200
我嘗試了很多不同的東西，但我一直得到相同的結果......當我嘗試在里面列印 nrooms 的值時，roomcomp我得到了指標值，所以如果我不得不猜測，我會說我打錯了道路...
uj5u.com熱心網友回復：
struct hotel *arr[]
是一個指標陣列，所以迭代器是指向指標的指標。
int roomcomp(const void *p1, const void *p2) {
const struct hotel *const *x = p1;
const struct hotel *const *y = p2;
return (*x)->nrooms - (*y)->nrooms;
uj5u.com熱心網友回復：
作為 KamilCuk 答案的替代方案，您可以首先避免創建指標陣列：
const size_t n_hotels = 4;
struct hotel *arr = malloc(n_hotels * sizeof(struct hotel));
arr[0].address = /* ... */;
arr[0].nrooms = /* ... */;
/* ... */
qsort(arr, n_hotels, sizeof(struct hotel), roomcomp);
現在傳遞給比較函式的東西將是struct hotel *你roomcomp所寫的。
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