Question

该程序应该创建一个排序列表，并按名字和姓氏对每个用户进行排序。我似乎无法弄清楚如何正确地对名称进行排序。

我只有append_to_list函数的问题，其余的函数运行正常。

当我第一次开始输入名字时：

user ID:    Last Name:    First Name:
3                Alex          Alex
2                Jones         Alex
1                andrew        john

它排序很好，直到我输入一个应在两个名称之间排序的名称当我输入安德鲁的名字时，亚历克斯就会发生这种情况。

 user ID:    Last Name:    First Name:
 4                Andrew        Alex
 3                Alex          Alex
 2                Jones         Alex
 1                andrew        john

但安德鲁，亚历克斯应该在用户2和3之间

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "user.h"
#include "readline.h"

// function append_to_list takes user input from user, id, name and puts it     to the end of the list
// as well as sorts each name alphabetically
struct user *append_to_list(struct user *family)
{
    struct user *cur, *prev, *new_node;

    // generate memory
    new_node = malloc(sizeof(struct user));

    if (new_node == NULL) { 
        printf("malloc failed in append\n");
        return family;
    }

    printf("Enter user ID: \n");
    scanf("%d", &new_node->number);
    printf("Enter user last name: \n");
    read_line(new_node->last_name,NAME_LEN);
    printf("Enter user first name: \n");
    read_line(new_node->first_name,NAME_LEN);

    for( cur=family; cur != NULL; cur = cur->next) {
        if (new_node->number == cur->number) {
                printf("user already exists: %s, %s\n",new_node->first_name,     new_node->last_name);
                free(new_node);
                return family;
        }   
    }       
    for (cur=family, prev = NULL; cur != NULL 
        && (strcmp(new_node->first_name,cur->first_name) < 0) 
        && (strcmp(new_node->last_name,cur->last_name) < 0); 
            prev = cur, cur = cur->next) { 

        if((strcmp(new_node->last_name,cur->last_name) < 0)) break;

        if((strcmp(new_node->first_name,cur->first_name) == 0)) 

        if((strcmp(new_node->first_name,cur->first_name) < 0)) break;
        ;
        }
        // use strcmp == 0 to see if name already exists
        if (cur != NULL && (strcmp(new_node->first_name,cur->first_name) == 0)
            && (strcmp(new_node->last_name,cur->last_name)) == 0) 
        {
                printf("user already exists: %s, %s\n",new_node->first_name, new_node->last_name);
                free(new_node);
                return family;
        }

    // append the linkedlist to the end
    new_node->next = cur;
    // check to see if the node is empty
    if (prev == NULL) {
        return new_node;
    } else  {
        prev->next = new_node->next;
        return family;
    }
}
// function delete_from_list removes a user from the family
struct user* delete_from_list(struct user *family) 
{
    struct user *prev, *cur;
    int id;
    int not_found = 0;
    printf("Enter user ID: \n");
    scanf("%d", &id);

    for (cur = family, prev = NULL; cur != NULL; prev = cur, cur = cur->next) {
        if (id == cur->number) {
                // if only one user on family
            if (prev == NULL) {
                family = cur->next;
            // if user is in the middle of family
            // connects prev node to cur node
            } else {
                prev->next = cur->next;
            }
            printf("user deleted: %s ,%s\n",cur->first_name, cur->last_name);
            free(cur);
        }
        else 
            not_found = 1;
    }
    if (not_found == 1) {
        printf("user not found\n");
    }
    return family;
}   
// function find_user searches the family by ID and matches it with the users name
void find_user(struct user *family)
{
    struct user *p = family;
    int id;
    int count = 0;
printf("Enter user ID: \n");
scanf("%d", &id);

    // compares the family with the user entered ID
    // if the ID is the same count set to 1
    if (p != NULL) {
        for (p = family; p != NULL; p = p->next) {
            if (id == p->number) {
                count = 1;
                break;
            }
        }
    }
    // if count is 1 we know the function found that specific user
    if ( count == 1) {
        printf("user found: %s, %s\n", p->last_name, p->first_name);
    } else {
        printf("user not found");
    }
}

// function printList prints the entire family
void printList(struct user *family)
{
    struct user *p;
    printf("user ID:\tLast Name:\tFirst Name:\n");
    for (p = family; p != NULL; p = p->next) {
        printf("%d\t\t%s\t\t%s\n", p->number, p->last_name, p->first_name);
    }

}

// function clearList clears the entired linked list
void clearList(struct user *family)
{
    struct user *p;
    while (family != NULL) {
        p = family;
        family = family->next;
        if (p != NULL) {
            free(p);
        }
    }
}

Answer 1

问题在于比较节点：

for (cur=family, prev = NULL; cur != NULL 
    && (strcmp(new_node->first_name,cur->first_name) < 0) 
    && (strcmp(new_node->last_name,cur->last_name) < 0); 
        prev = cur, cur = cur->next) { ... }

您应该跳过具有较小系列或（相同姓氏和较小名字）的节点。以这种方式修复比较：

for (cur=family, prev = NULL;
     cur != NULL 
     && ((strcmp(new_node->first_name, cur->first_name) < 0) 
     ||  ((strcmp(new_node->first_name, cur->first_name) == 0)
     &&   (strcmp(new_node->last_name,cur->last_name) < 0))); 
     prev = cur, cur = cur->next) { ... }

简化后续代码。你实际上不需要任何代码。循环将在插入点停止。只检查是否存在相同的姓氏和名字（但如果有2个John会怎么样？）并在prev和cur之间插入，或者在family之前插入prev是NULL。

for循环看起来很难看：难以阅读，容易出错。编写一个单独的比较函数，它接受2个节点并根据电话簿顺序返回-1, 0, +1。您将对append_to_list和delete_from_list使用此函数，编写更少的代码，更具可读性和更一致性。

Answer 2

我认为重叠比较运算符是一个更好的主意，然后用一些存在的算法对你的列表进行排序。

Answer 3

此循环中的条件有问题：

 for (cur=family, prev = NULL;
        cur != NULL && (strcmp(new_node->first_name,cur->first_name) < 0) 
                    && (strcmp(new_node->last_name,cur->last_name) < 0); 
                prev = cur, cur = cur->next)

循环不会执行：

(cur=family, family exist)
cur != NULL -> True
(Alex == Alex)
((strcmp(new_node->first_name,cur->first_name) -> 0) < 0 -> False
(Andrew > Alex)
((strcmp(new_node->last_name,cur->last_name) -> 1) < 0 -> False
True && False && False -> False

因此，您将在开头添加新记录。

此外，在循环中你有一个不好的＆＃39;如果＆＃39;代码：

if((strcmp(new_node->first_name,cur->first_name) == 0)) 

if((strcmp(new_node->first_name,cur->first_name) < 0)) break;
;

Doc. strcmp

提示：删除有问题的无用代码。 振作！

Answer 4

for循环将在插入点处停止（在上一个节点与cur节点之间）。

即使new_node大于最后一个节点，下一部分也会对列表进行排序。如果新节点大于最后一个节点，则cur变为null，// //分配给new_node_> next。因此，prev等于cur；因此，prev-> next = new_node;

           for (cur=family, prev = NULL; cur!=NULL && ((strcmp(new_node->first_name,
           cur->first_name)>0) || ((strcmp(new_node->first_name,
            cur->first_name)==0)&&(strcmp(new_node->last_name,
            cur->last_name)>0))); prev = cur, cur = cur->next);

      new_node->next = cur;
           if(prev==NULL)
            return new_node;
           else {
           prev->next = new_node;
           return family;
           }

C程序排序链表

4 个答案: