我有一个奇怪的问题:
int cmp(const void *a, const void *b) {
const char *ia = (const char *) a;
const char *ib = (const char *) b;
return strcmp(ia, ib);
}
char ** names = NULL;
if((names = (char **) calloc(3,sizeof(char*))) == NULL)
{
fprintf(stderr,"Unable to allocate the memory");
return 1;
}
...
names[0] = "c";
names[1] = "b";
names[2] = "a";
printf("before\n");
printf("%s\n",names[0]);
printf("%s\n",names[1]);
printf("%s\n",names[2]);
qsort(names,3,sizeof(char *),cmp);
printf("after\n");
printf("%s\n",names[0]);
printf("%s\n",names[1]);
printf("%s\n",names[2]);
按预期给出:
before
c
b
a
after
a
b
c
但是
names[0] = (char *) calloc(1024,sizeof(char));
names[1] = (char *) calloc(1024,sizeof(char));
names[2] = (char *) calloc(1024,sizeof(char));
scanf("%s",names[0]);
scanf("%s",names[1]);
scanf("%s",names[2]);
printf("before\n");
printf("%s\n",names[0]);
printf("%s\n",names[1]);
printf("%s\n",names[2]);
qsort(names,3,sizeof(char *),cmp);
printf("after\n");
printf("%s\n",names[0]);
printf("%s\n",names[1]);
printf("%s\n",names[2]);
给予
before
c
b
a
after
b
a
c
为什么字符串排序不正确?
最佳答案
您的比较函数接收数组中项目的地址。您需要取消引用以获取数组中的指针:
int cmp(const void *a, const void *b) {
const char *ia = *(const char **) a;
const char *ib = *(const char **) b;
return strcmp(ia, ib);
}
关于c - 对动态分配的字符串进行排序,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/5035289/