b中的bsearch函数

Question

如果我有两个功能：

void SortStudents(char *studentList[], size_t studentCount) 
{
    qsort(studentList, sizeof(studentList)/sizeof(studentList[0]), sizeof(studentList[0]), Compare);
}

int Compare(const void *a, const void *b) 
{
    return (strcmp(*(char **)a, *(char **)b));
}

使用qsort函数进行排序和比较，如何使用bsearch查找列表的子集。 例如，如果我有两个列表：

• （列表A）Bob，Jimmy，Lee，James，Anne
• （名单B）Jen，Jon，Lee，James，Steph

如何在列表B中搜索以在A中查找这些元素？

您是否也可以在列表B中进行搜索以查找不在A中的元素？

谢谢。

Answer 1

要进行搜索，您必须使用单项列表作为'bsearch（）'的关键参数。

在上下文中，在b_list中的a_list[n]中搜索条目：

 void *found = bsearch(&a_list[n], b_list, b_list, b_size, Compare);

因此，要查找列表B中列表A中的元素，您将执行以下操作：

• 排序列表B（除非您愿意，否则不需要为练习的这一部分对列表A进行排序）
• 对于列表A中的每个元素，搜索（已排序）列表B中的项目。

要查找B中不在A中的元素，您需要对列表A进行排序，然后对列表B中的每个元素进行排序，使用反向搜索查看该元素是否在列表A中。

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static char *a_list[] = { "Bob", "Jimmy", "Lee", "James", "Anne"  };
static char *b_list[] = { "Jen", "Jon",   "Lee", "James", "Steph" };
static size_t a_number = sizeof(a_list)/sizeof(a_list[0]);
static size_t b_number = sizeof(b_list)/sizeof(b_list[0]);

static int Compare(const void *a, const void *b) 
{
    return (strcmp(*(char **)a, *(char **)b));
}

void SortStudents(char *studentList[], size_t studentCount) 
{
    qsort(studentList, studentCount, sizeof(studentList[0]), Compare);
}

static void dump_list(const char *tag, char **list, size_t number)
{
    size_t i;
    printf("%s:\n", tag);
    for (i = 0; i < number; i++)
        printf(" %s%s", list[i], (i == number - 1) ? "" : ",");
    putchar('\n');
}

static char *search_list(char *name, char **list, size_t number)
{
    char **found = bsearch(&name, list, number, sizeof(*list), Compare);
    return((found == 0) ? 0 : *found);
}

static void names_in_list(char **find_list, size_t find_number, char **name_list, size_t name_number)
{
    size_t i;
    for (i = 0; i < find_number; i++)
    {
        char *name = search_list(find_list[i], name_list, name_number);
        if (name != 0)
            printf("Found %s in list at %s\n", find_list[i], name);
    }
}

static void names_not_in_list(char **find_list, size_t find_number, char **name_list, size_t name_number)
{
    size_t i;
    for (i = 0; i < find_number; i++)
    {
        char *name = search_list(find_list[i], name_list, name_number);
        if (name == 0)
            printf("Did not find %s in list\n", find_list[i]);
    }
}

int main(void)
{
    dump_list("Unsorted A list", a_list, a_number);
    dump_list("Unsorted B list", b_list, b_number);
    SortStudents(a_list, a_number);
    SortStudents(b_list, b_number);
    dump_list("Sorted A list", a_list, a_number);
    dump_list("Sorted B list", b_list, b_number);
    dump_list("Searching in B list for people in A list", b_list, b_number);
    names_in_list(a_list, a_number, b_list, b_number);
    dump_list("Searching in A list for people not in B list", a_list, a_number);
    names_not_in_list(b_list, b_number, a_list, a_number);
    return(0);
}

---

输出是：

Unsorted A list:
 Bob, Jimmy, Lee, James, Anne
Unsorted B list:
 Jen, Jon, Lee, James, Steph
Sorted A list:
 Anne, Bob, James, Jimmy, Lee
Sorted B list:
 James, Jen, Jon, Lee, Steph
Searching in B list for people in A list:
 James, Jen, Jon, Lee, Steph
Found James in list at James
Found Lee in list at Lee
Searching in A list for people not in B list:
 Anne, Bob, James, Jimmy, Lee
Did not find Jen in list
Did not find Jon in list
Did not find Steph in list