所以，我尝试用C++中的套接字编程在客户端和服务器之间发送数据。现在，我在StackOverflow中读到了一个答案，其中提到我们必须检查每次发送时接收到多少原始msg，然后等待，直到我们完全获得信息。为此，我使用了以下sendMsg（）和receive（）函数。

string receive()
    {
        string msg = "";
        char last_character = '%';
        do
        {
            char buffer[2048] = {0};
            read(sockfd, buffer, 2048);
            string s(buffer);
            msg += s;
            last_character = s[s.size() - 1];
        } while (last_character != '|');
        return msg.substr(0, msg.size() - 1);
    }
    bool sendMsg(string s)
    {
        s += '|';
        char buffer[s.size()];
        strcpy(buffer, &s[0]);
        int bytes_total = 0;
        int bytes_left = s.length();
        int bytes_now = 0;
        while (bytes_left > 0)
        {
            bytes_now = send(sockfd, &buffer[bytes_total], bytes_left, 0);
            if (bytes_now == -1)
            {
                err("Error sending message");
                return false;
            }
            assert(bytes_now <= bytes_left);
            bytes_left -= bytes_now;
            bytes_total += bytes_now;
        }

        return true;
    }

这在大多数情况下都很好用，只是有时会添加一个“|'字符，即消息前的分隔符。当我将一个新客户端连接到服务器，并尝试向客户端发送一些消息以在其控制台中打印时，这个问题就很突出。类似于以下内容：

usernames[username] = client_socket;
    comm.sendMsg(string(GRN) + "Username accepted.\n" + string(NRM));
    cout << GRN << username << " connected." << NRM << endl;
    comm.sendMsg(readme(username));

其中，用户名是一个无序Map，它存储每个唯一用户名的客户端套接字，自述文件函数只是一个字符串，如“欢迎来到聊天室“，+用户名。这里，#define NRM“\x1B[0m”，#define GRN“\x1B[32m”
所以，有时我得到的输出是

Enter the IP address of the server: l
Connected to server.
Enter your username: user
Username accepted.
|
+------------------------------------------------------------+
|                                                            |
|   [server]: Welcome to the chatroom, user                  |
|                                                            |
|   [server]: Here are the commands you can use:             |
|                                                            |
|   1. status             : Lists the status of all users    |
|   2. connect [username] : Connect to username to start     |
|                           chatting                         |
|   3. goodbye            : Ends current chatting session    |
|   4. close              : Disconnects the user from the    |
|                           server                           |
|   5. clear              : Clears the chat from the window  |
|   6. Ctrl + C (client)  : Disconnects the client and       |
|                           terminates its chat session      |
|                           if present                       |
|   7. Ctrl + C (server)  : Terminates the server and all the|
|                           clients connected to the server  |
+------------------------------------------------------------+

您可以注意到|就在Username accepted行之后，这是不必要的。我无法找出问题所在。是sendMsg和receive函数有问题吗？或者没问题，我必须查看其余代码。客户端和服务器文件接近700行C++代码，所以我没有直接在这里发布。
编辑：我修改了接收函数如下：

string receive()
    {
        string msg = "";
        char last_character = '%';
        while (last_character != '|')
        {
            char buffer[2048] = {0};
            int bytes_read = read(sockfd, buffer, 2048);
            if (bytes_read <= 0)
            {
                err("Error receiving message");
                return "";
            }
            string s(buffer, bytes_read);
            for (int i = 0; i < s.size() - 1; i++)
                if (s[i] == '|')
                {
                    s.erase(s.begin() + i);
                }
            msg += s;
            last_character = s[s.size() - 1];
        }
        return msg.substr(0, msg.size() - 1);
    }