c++ - 如何正确实现 select 以正确从 stdin 和 recv() 获取数据

Question

这是我的问题的延续：我在 C++ 中对 netcat 的尝试不会让我从服务器得到回复，以便更好地了解我推荐阅读的情况。据我了解，问题在于程序可以从标准输入获取数据，也可以同时从两者获取getline()数据recv()。所以我需要使用select()检查状态recv()来查看是否有任何数据要输出。我一直在研究 Unix 文件描述符并使用它，select()但是我似乎不太了解，或者至少我不知道如何将这些示例应用到我的程序中。那么，我怎样才能正确地调用select()我的代码以便正确地从中获取数据recv()呢？ 我的代码：

#include <iostream>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <cstring>
#include <stdlib.h>
#include <errno.h>

using namespace std;

int main (int argc, char** argv) {
    if (argv[1] == NULL) {
        cout << "\033[31mTARGET NOT SPECIFIED - TERMINATING...\033[0m\n";
        return -1;
    }
    if (argv[2] == NULL) {
        cout << "\033[31mPORT NOT SPECIFIED - TERMINATING...\033[0m\n";
        return -2;
    }
    
    string target = argv[1];
    int port = atoi(argv[2]);

    cout << "GENERATING SOCKET...\n";
    int chatter = socket(AF_INET, SOCK_STREAM, 0);
    if (chatter == -1) {
        cout << "\033[31mSOCKET GENERATION FAILURE - TERMINATING...\033[0m\n";
        return -3;
    }
    cout << "\033[32mSUCCESSFULLY GENERATED SOCKET\033[0m\n";

    struct sockaddr_in hint;
    hint.sin_family = AF_INET;
    hint.sin_port   = htons(port);
    inet_pton(AF_INET, target.c_str(), &hint.sin_addr);

    cout << "CONNECTING TO " << target << " AT PORT " << port << "...\n";   
    int connection_status = connect(chatter, (sockaddr*)&hint, sizeof(hint));
    if (connection_status == -1) {
        cout << "\033[31mCONNECTION FAILURE - TERMINATING...\033[0m\n";
        return -4;
    }
    cout << "\033[32mCONNECTED TO HOST\033[0m\n";

    char buf[4096] = {0};
    string msg;
    while (true) {
        getline(cin, msg);
        msg+"\r\n";
        int sendmsg = send(chatter, msg.c_str(), msg.size()+1, 0);
        if (sendmsg == -1) {
            cout << "\033[31mMESSAGE SENDING FAILURE - TERMINATING...\033[0m\n";
            return -5;
        }
        int byterecv = recv(chatter, buf, 4096, 0);
        if (byterecv == -1) {
            cout << "\033[31mFAILURE TO RECEIVE MESSAGE - TERMINATING...\033[0m\n";
            return -6;
        }
        cout << byterecv << "\n";
        cout << buf << "\n";
    }

    close(chatter);

    return 0;
}

虽然我需要帮助来修复程序，但我也认为了解 select 将如何用于它将有助于教会我关于它以及如何在将来使用它。

标签： c++linuxsocketsselectfile-descriptor