qsort给出[错误]:从`int(*)(cricketer*,cricketer*)'到`int(*)(const void*,const void*)'的无效转换

Question

这是代码,它通过avg运行对板球运动员的数据进行排序.该qsort函数显示错误:

[错误] C:\用户\编码器\文件\ C-免\ TEMP\Untitled3.cpp:29:错误:从无效转变int (*)(cricketer*, cricketer*)至 int (*)(const void*, const void*)

[错误] C:\ Users\Encoder\Documents\C-Free\Temp\Untitled3.cpp:29:错误:初始化`void qsort的参数4(void*,size_t,size_t,int()(const void,const void)*))"

包括

#include<stdlib.h>
struct cricketer  //structure for details of cricketer
{
    int avg_run;
    char name[20];
    int age;
    int match_no;
} c[4];
int sort(struct cricketer *a, struct cricketer *b);   //pre-defining sort function 
int main()     //main function
{
    int i, s;
    for (i = 0; i < 3; i++)    //enumerating structure records.
    {
        printf("enter the name of cricketer ");
        fflush(stdin);
        gets(c[i].name);
        printf("enter his age,his no of matches and total average runs ");
        scanf("%d%d%d",&c[i].age, &c[i].match_no, &c[i].avg_run);
        }
    printf("records before sorting");  
    for (i = 0; i < 3; i++)
    {
        printf("\n\nname ");
        puts(c[i].name);
        printf("age %d\nno of matches %d\naverage runs %d\n",c[i].age, c[i].match_no, c[i].avg_run);
    }
    qsort(c, 3, sizeof(c[0]), sort); //sorting using qsort
    printf("\nrecords after sorting");
    for (i = 0; i < 3; i++)
    {
        printf("\n\nname ");
        puts(c[i].name);
        printf("age %d\nno of matches %d\naverage runs %d\n",c[i].age, c[i].match_no, c[i].avg_run);
    }
}
int sort(struct cricketer *a, struct cricketer *b)  //sort function definition
{
    if (a->avg_run == b->avg_run)
        return 0;
    else 
        if ( a->avg_run > b->avg_run)
            return 1;
        else 
            return -1;
}

Answer 1

要传递给它的指针的函数qsort必须是

int sort(const void* va, const void* vb);

因为这是qsort预期的.然后在该功能中你必须在开始时做

const struct cricketer *a = (struct cricketer*) va;
const struct cricketer *b = (struct cricketer*) vb;

或者,如果您更喜欢使用点.而不是箭头访问->

const struct cricketer a = *(struct cricketer*) va;
const struct cricketer b = *(struct cricketer*) vb;

请参阅此参考中的示例

关于错误消息,这int (*)(cricketer*, cricketer*)是一个指向函数的指针,该函数获得2个指针cricketer作为参数.编译器需要这样一个函数指针int (*)(const void, const void*),它告诉你它不能将前者转换为后者.还要注意你需要如何指向const数据,因为sort不应该修改数据.