[英]Why doesn't qsort() work when I use it to sort an array of strings?
I'm trying to sort this list of strings: ["a", "z", "b"]. 我正在尝试对以下字符串列表进行排序:[“ a”,“ z”,“ b”]。 So the answer should be ["a", "b", "z"].
因此答案应该是[“ a”,“ b”,“ z”]。 However, when I try to use C's qsort(), nothing moves!
但是,当我尝试使用C的qsort()时,没有任何动作! What am I doing wrong?
我究竟做错了什么?
MWE: MWE:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int sortcmpfunc (const void *a, const void *b)
{ return strcmp((const char*)a, (const char*)b); }
int main(){
const char** list = (const char**)malloc(50*sizeof(const char*));
for(int i = 0; i < 50; i++){
list[i] = (char*)malloc(50*sizeof(char));
}
list[0] ="a";
list[1] = "z";
list[2] = "b";
for (int i=0; i<3; i++){ printf("%s ", list[i]); } printf("\n");
qsort(list, 3, sizeof(const char*), sortcmpfunc);
for (int i=0; i<3; i++){ printf("%s ", list[i]); } printf("\n");
return 0;
}
Output with gcc test-qsort.c && ./a.out
: 用
gcc test-qsort.c && ./a.out
输出:
a z b
a z b
Simply 只是
strcmp(*(char **) a, *(char **) b);
note that a pointer to each element is passed to the comparison function, hence you need to cast to the correct type and dereference. 请注意,指向每个元素的指针将传递给比较函数,因此您需要强制转换为正确的类型和取消引用。
And please avoid 而且请避免
for (int i=0; i<3; i++){ printf("%s\n", list[i]); }
and instead write 然后写
for (int i = 0; i < 3; i++) {
printf("%s\n", list[i]);
}
it's horrible 这太糟糕了
And also use 并使用
gcc -Wall -Werror test-qsort.c && ./a.out
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