将指针数组快速排列到结构中

Question

我正在尝试使用C提供的内置快速排序来排序指向结构的指针数组。我想根据结构中的名称元素对每个元素进行排序。

尽管我每次通过比较函数调试整个数组的输出时，都表明该函数的确在切换元素，但最终的结果并不是正确的排序顺序。有什么我只是没有看到这里？

typedef struct // The custom data type. 
{ 
    char *name; 
} Person; 

---------------------------- 

Person **people; // A dynamically allocated array of Person pointers. 
int numPeople; // The logical index of people. 
int maxPeople; // The current maximum capacity of people. 

int compare(const void *a, const void *b) // The comparison function for determining 
{           // alphabetic ordering. 
    const Person *const *p1 = a; 
    const Person *const *p2 = b; 
    return strcmp((*p1)->name, (*p2)->name); // Compare alphabetically, return result. 
} 

void SomeFunction(void) 
{ 
    qsort(people, numPeople, sizeof(Person *), compare); // Perform the sort. 
} 

感谢您的帮助。

Answer 1

尝试我已经测试你的代码，它看起来工作正常。这里是我用gcc 4.5.2编译的代码：

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

typedef struct // The custom data type. 
{ 
     char *name; 
} Person; 

Person **people; // A dynamically allocated array of Person pointers. 
int numPeople; // The logical index of people. 
int maxPeople; // The current maximum capacity of people. 

int compare(const void *a, const void *b) // The comparison function for determining 
{           // alphabetic ordering. 
     const Person *const *p1 = a; 
     const Person *const *p2 = b; 
     return strcmp((*p1)->name, (*p2)->name); // Compare alphabetically, return result. 
} 

void SomeFunction(void) 
{ 
     qsort(people, numPeople, sizeof(Person *), compare); // Perform the sort. 
} 

int main() 
{ 
     int iCnt; 

     maxPeople = 4; 
     numPeople = 4; 

     people = calloc(1, sizeof(Person *) * maxPeople); 

     people[0] = calloc(1, sizeof(Person)); 
     people[1] = calloc(1, sizeof(Person)); 
     people[2] = calloc(1, sizeof(Person)); 
     people[3] = calloc(1, sizeof(Person)); 

     people[0]->name = strdup("Tanya"); 
     people[1]->name = strdup("Alfred"); 
     people[2]->name = strdup("Harry"); 
     people[3]->name = strdup("Oakley"); 

     for(iCnt = 0; iCnt < numPeople; iCnt ++) 
       printf("[%d] %s\n", iCnt, people[iCnt]->name); 

     SomeFunction(); 

     for(iCnt = 0; iCnt < numPeople; iCnt ++) 
       printf("[%d] %s\n", iCnt, people[iCnt]->name); 

     return 0; 
} 

该代码看起来是合法的，我不知道什么是错的。你可以尝试编译我测试过的代码并查看它是否有效？

Answer 2

你能与此

int compare(const void *a, const void *b) // The comparison function for determining 
{           // alphabetic ordering. 
    const Person *p1 = *(const Person**)a; 
    const Person *p2 = *(const Person**)b; 
    return strcmp((p1)->name, (p2)->name); // Compare alphabetically, return result. 
}