Question

我正在开发一个客户端 - 服务器程序，当我和我正在尝试使用此结构实现用户链接列表时：

typedef struct user {
    char username[50];
    int user_pid;
    struct user *next;
} user_list;

我正在尝试弄清楚代码有什么问题，因为编译器没有给我任何错误，但当我尝试用户打印用户列表时，它根本不会显示任何内容。

AddUser功能：

AddUser(user_list *head, req req)
{
    if(head == NULL)
    {
        head = malloc(sizeof(user_list));

        if (head == NULL) 
            fprintf(stdout,"[SERVER] Error memory allocation ");

        strcpy(head->username, req.str);
        head->user_pid = req.client_pid;
        head->next = NULL;
    }
    else
    {   
        user_list *current = head;

        while (current->next != NULL) 
            current = current->next;

        current->next = malloc(sizeof(user_list));
        strcpy(current->next->username, req.str);
        current->next->user_pid = req.client_pid;
        current->next->next = NULL;
    }
    num_users++;
}

主要功能（短版）

int Main()
{
struct request req;
struct answer ans;
user_list *head = NULL;

do{

    read(fifo_1, &req, sizeof(req)); // Read client request

    if(strcasecmp(req.str, "adduser") == 0) 
    {               
        AddUser(head, req);
        strcpy(ans.str, "User added with success! You're logged!");
    }

    if(strcasecmp(req.str, "users") == 0) // Print on the screen the users list
    {
        user_list *current = head;

        while (current != NULL) 
        {
            fprintf(stdout, "%s\n", current->username);
            fprintf(stdout, "%d\n", current->user_pid);
            current = current->next;
        }

    }
}while(strcmp(req.str,"exit") != 0);
}

Answer 1

将其他人已经在评论中指出的内容放在一起：

更改main。而不是
```
int Main()
```
使用
```
int main()
```

在head中更改main时，AddUser的值不会发生变化。这是一个解决方案。从AddUser返回head。

user_list* AddUser(user_list *head, req req)
{
    if(head == NULL)
    {
        head = malloc(sizeof(user_list));

        if (head == NULL) 
            fprintf(stdout,"[SERVER] Error memory allocation ");

        strcpy(head->username, req.str);
        head->user_pid = req.client_pid;
        head->next = NULL;
    }
    else
    {   
        user_list *current = head;

        while (current->next != NULL) 
            current = current->next;

        current->next = malloc(sizeof(user_list));
        strcpy(current->next->username, req.str);
        current->next->user_pid = req.client_pid;
        current->next->next = NULL;
    }
    num_users++;
    return head;
}

在AddUser中捕获main的返回值。而不仅仅是
```
AddUser(head, req);
```
使用
```
head = AddUser(head, req);
```

内存分配代码错误

1 个答案: