英文:
How to sort an array** by a struct variable in C?
问题
以下是您要翻译的部分：
我最近一直在尝试使用qsort函数对数组中的结构进行排序。我从.csv文件加载了一个数组**。我的结构如下：
typedef struct {
int id;
char regionName[25];
char townName[25];
int countOfMan;
int countOfWoman;
} tTown;
我想按照地区中的女性数量对数组进行排序。我已经定义了比较函数并尝试进行排序。
int compareWomenCount(const tTown* village1, const tTown* village2) {
int result = 0;
if (village1->countOfWoman < village2->countOfWoman) {
result = -1;
}
else if (village1->countOfWoman > village2->countOfWoman) {
result = 1;
}
return result;
}
这是我的qsort函数：
void sortArray(tTown** region, int arrayLength) {
qsort(region, arrayLength, sizeof(tTown*), compareWomenCount);
}
但它没有起作用。有人知道该怎么办吗？
谢谢！
英文:
I have been recently up to a sorting structures in an array by a function qsort. I loaded an array** from .csv file. My structure looks like this.
typedef struct {
int id;
char regionName[25];
char townName[25];
int countOfMan;
int countOfWoman;
} tTown;
I want to sort an array by amount of women in region. I have defined compare function and tried to sort it.
int compareWomenCount(const tTown* village1, const tTown* village2) {
int result = 0;
if (village1->countOfWoman < village2->countOfWoman) {
result = -1;
}
else if (village1->countOfWoman > village2->countOfWoman) {
result = 1;
}
return result;
}
This is my qsort:
void sortArray(tTown** region, int arrayLength) {
qsort(region, arrayLength, sizeof(tTown*), compareWomenCount);
}
But it didn't work. Has anyone a clue, what to do?
Thank you!
答案1
得分: 0
The qsort 函数将数组的每个元素的指针传递给比较函数（基本上它在每个元素上使用地址操作符 &，就像 &region[i]）。
如果数组中的每个元素都是指针，那么传递的是一个指向指针的指针。
这意味着您的比较函数应该如下所示：
int compareWomenCount(const tTown** village1, const tTown** village2) {
int result = 0;
if ((*village1)->countOfWoman < (*village2)->countOfWoman) {
result = -1;
}
else if ((*village1)->countOfWoman > (*village2)->countOfWoman) {
result = 1;
}
return result;
}
此外，排序函数的参数需要是通用的常量指针（const void *）以确保正确，然后在函数内部将它们强制转换为正确的指针类型。
英文:
The qsort function passes a pointer to each element of the array to the comparison function (basically it uses the address-of operator & on each element, as in &region[i]).
If each element in the array is a pointer, what is passed is a pointer to a pointer.
That means your comparison function will need to look like
int compareWomenCount(const tTown** village1, const tTown** village2) {
int result = 0;
if ((*village1)->countOfWoman < (*village2)->countOfWoman) {
result = -1;
}
else if ((*village1)->countOfWoman > (*village2)->countOfWoman) {
result = 1;
}
return result;
}
Furthermore, the arguments of the sorting function needs to generic constant pointers (const void *) to be really correct, and then you should cast them to the correct pointer type inside the function.
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