为 qsort 编写比较函数
我正在编写一个比较函数，该函数通过姓氏的升序来比较和组织名称，如果两个姓氏相同，则按名字的降序排列。我现在拥有的功能不会这样做。
这是函数：
int namecmp(const void *p, const void *q)
{
const name *pp = p;
const name *qq = q;
int n;
if((n = strcmp(pp->last, qq->last)) != 0)
return n;
return qq->first - pp->first;
}
我正在尝试组织一个动态结构数组，这是我的结构。
typedef struct
{
char last[NAMESIZE];
char first[NAMESIZE];
}name;
typedef struct
{
int id;
name name;
float score;
}record;
typedef struct {
record *data; /* the dynamic array */
size_t nalloc; /* number of records allocated */
size_t nused; /* number of records in use */
} record_list;
下面是 qsort 的调用方式。
qsort(list->data, list->nused, sizeof(list->data[0]), namecmp);
任何帮助将不胜感激。
编辑：我按照你的建议做了，现在我有错误的输出。
我的输出是：
3456789 Burns, Monty: 100.00
4567890 Simpson, Lisa: 95.00
1234567 Simpson, Homer: 35.50
6666666 Simpson, Bart: 45.00
2345678 Flanders, Ned: 99.50
编辑2：
我如何将字符串存储到结构中。
if(sscanf(line,"%s", lastname) == 1)
{
if(strlen(lastname) < NAMESIZE)
{
lastname[0] = toupper((int)lastname[0]);
strcpy(rec->name.last, lastname);
break;
}
}
I'm writing a comparision function that compares and organizes names by ascending order of last name and if both last names are the same, descending order of first names. The function I have right now will not do that.
Here is the function:
int namecmp(const void *p, const void *q)
{
const name *pp = p;
const name *qq = q;
int n;
if((n = strcmp(pp->last, qq->last)) != 0)
return n;
return qq->first - pp->first;
}
I am trying to organize a dynamic array of structures, here are my structures.
typedef struct
{
char last[NAMESIZE];
char first[NAMESIZE];
}name;
typedef struct
{
int id;
name name;
float score;
}record;
typedef struct {
record *data; /* the dynamic array */
size_t nalloc; /* number of records allocated */
size_t nused; /* number of records in use */
} record_list;
and here is how qsort is called.
qsort(list->data, list->nused, sizeof(list->data[0]), namecmp);
Any help would be appreciated.
EDIT: I did what you suggested now i have the wrong output.
my output is:
3456789 Burns, Monty: 100.00
4567890 Simpson, Lisa: 95.00
1234567 Simpson, Homer: 35.50
6666666 Simpson, Bart: 45.00
2345678 Flanders, Ned: 99.50
EDIT 2:
How i store string into the structure.
if(sscanf(line,"%s", lastname) == 1)
{
if(strlen(lastname) < NAMESIZE)
{
lastname[0] = toupper((int)lastname[0]);
strcpy(rec->name.last, lastname);
break;
}
}
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评论（2）
您还需要对名字调用 strcmp ，否则这将不起作用（因为这只是减去内存中的地址）。将最后一行更改为
You need to call strcmp on the first name as well or this will not work (as that's just subtracting addresses in memory). Change the last line to
比较函数有两个比较（已编辑的一个），但顺序不同。
首先有 strcmp(p, q) 和 return 语句有 strcmp(q,p)。让它们相同，它就会起作用！
沙什
The comparison function has two comparisons (Edited one), but in different order.
First has strcmp(p, q) and return statement has strcmp(q,p). Make them same, and it ll work !!
Shash