使用qsort()对包含字符串的结构的指针进行排序 [英] using qsort() to sort pointers to structs containing strings
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问题描述
我不确定这是否可以与qsort一起使用,因为我要排序的内容(指向结构的指针数组)不是我要比较的内容(字符串).
I'm not sure if this is possible to do with qsort because what I want to sort (array of pointers to struct) is not what I am comparing (strings).
这是我程序的简化版(假设所有学生数据在我们调用qsort()之前都处于核心位置,并且n是要排序的记录数):
Here is an abridged version of my program (assume that all the student data is in core before we call qsort() and n is the number of records to sort):
struct student {
char lname[NAMESIZE + 1];
char fname[NAMESIZE + 1];
short mid;
short final;
short hmwks;
};
int cmp(const void *, const void *);
int
main(int argc, char **argv)
{
int n;
struct student *data[MAX];
qsort(data, n, sizeof(struct student *), cmp);
return 0;
}
int
cmp(const void *p0, const void *p1)
{
return strcmp((*(struct student *) p0).lname,
(*(struct student *) p1).lname);
}
推荐答案
应该是这样的:
int
cmp(const void *p0, const void *p1)
{
// pn is a pointer to an element of the array,
// so, it's effectively a pointer to a pointer to a struct.
// Therefore, we need to cast it appropriately to struct student **.
// To get a pointer to a struct from it, we dereference it once,
// hence the "*". Then we need to extract a pointer to the beginning
// of a string, hence the "->".
return strcmp((*(struct student **) p0)->lname,
(*(struct student **) p1)->lname);
}
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