下面的 c++ 程序应该使用套接字数据报将每一行转换为大写，以便在两个线程之间进行通信。

Example:
Hello World!<return>
HELLO WORLD!
123abc!<return>
123ABC!
<return>
<end program>

编写的程序对我有用，但是如果我在主程序中注释 bugfix() 函数调用，程序会在第一行输入后无限期等待。

Example:
Hello World!<return>
<the program wait indefinitely>

这发生在 Windows 7 上，最后一次更新是 10/04/2011 使用最后一个 MinGW32。

#include <iostream>
#include <cstdlib>
#include <cctype>
#include <sys/types.h>
#include <winsock.h>
#include <windows.h>
#include <process.h>

using namespace std;

#define CHECK(exp, cond)  do { typeof(exp) _check_value_ = exp; check(_check_value_ cond, _check_value_, __LINE__, #exp #cond); } while(0)

template <class T>
void check(bool ok, T value, int line, const char* text) {
    if (!ok) {
        cerr << "ERROR(" << line << "):" << text << "\nReturned: " << value << endl;
        cerr << "errno=" << errno << endl;
        cerr << "WSAGetLastError()=" << WSAGetLastError() << endl;
        exit(EXIT_FAILURE);
    }
}

#define DATA_CAPACITY   1000
#define PORT            23584
#define TEST_IP         "192.0.32.10"
#define MYSELF          "127.0.0.1"
#define DST_IP          MYSELF

sockaddr_in address(u_long ip, u_short port) {
    sockaddr_in addr = { };
    addr.sin_family = AF_INET;
    addr.sin_port = port;
    addr.sin_addr.s_addr = ip;
    return addr;
}

void __cdecl client_thread(void* args) {
    SOCKET s = *(SOCKET*)args;

    sockaddr_in addr = address(inet_addr(DST_IP), htons(PORT));

    char data[DATA_CAPACITY];
    while (1) {
        cin.getline(data, DATA_CAPACITY);
        int data_len = strlen(data);

        CHECK(sendto(s, data, data_len, 0, (sockaddr*)&addr, sizeof addr), >= 0);
        CHECK(recvfrom(s, data, DATA_CAPACITY, 0, NULL, NULL), >= 0);

        cout << data << endl;

        if (data_len == 0)
            break;
    }

    CHECK(closesocket(s), == 0);
}

void __cdecl server_thread(void* args) {
    SOCKET s = *(SOCKET*)args;
    sockaddr_in addr = address(INADDR_ANY, htons(PORT));
    int addr_size = sizeof addr;
    CHECK(bind(s, (sockaddr*)&addr, sizeof addr), != SOCKET_ERROR);

    char data[DATA_CAPACITY];
    while (1) {
        int data_len = recvfrom(s, data, DATA_CAPACITY, 0, (sockaddr*)&addr, &addr_size);
        CHECK(data_len, >= 0);

        for (int i = 0; i < data_len; i++)
            if (islower(data[i]))
                data[i] = toupper(data[i]);

        CHECK(sendto(s, data, data_len, 0, (sockaddr*)&addr, addr_size), >= 0);

        if (data_len == 0)
            break;
    }

    CHECK(closesocket(s), == 0);
}

// This function create a TCP connection with www.example.com and the close it
void bugfix() {
    SOCKET s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    sockaddr_in addr = address(inet_addr(TEST_IP), htons(80));
    connect(s, (sockaddr*)&addr, sizeof addr);
    CHECK(closesocket(s), == 0);
}

int main()
{
    cout << "Convert text to uppercase, an empty line terminate the program" << endl;


    WSADATA wsaData;
    CHECK(WSAStartup(MAKEWORD(2, 2), &wsaData), == 0);

    SOCKET client = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
    SOCKET server = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);

    CHECK(client, != INVALID_SOCKET);
    CHECK(server, != INVALID_SOCKET);

    // if this function is not called the program doesn't work
    bugfix();

    HANDLE hClient = (HANDLE)_beginthread(client_thread, 0, &client);
    HANDLE hServer = (HANDLE)_beginthread(server_thread, 0, &server);

    HANDLE h[] = { hClient, hServer };

    WaitForMultipleObjects(sizeof h / sizeof *h, h, TRUE, INFINITE);

    CHECK(WSACleanup(), == 0);

    return EXIT_SUCCESS;
}

最佳答案

    int data_len = strlen(data);

Tony Hoare 将他对 NULL 指针的定义称为他的十亿美元错误。以零结尾的字符串一定是丹尼斯·里奇 (Dennis Ritchie) 犯的一百亿美元的错误。加一个。

否则您的程序是发现 UDP 不是可靠协议(protocol)的精心设计的方法。允许网络堆栈任意使 UDP 数据包消失或重新排序。只要在它上面有另一个协议(protocol)可以检测到这一点，就像 TCP 一样，这就可以了。你在没有这种创可贴的情况下飞行，bugfix() 实际上不是解决方法。

使用 TCP，首先发送数据包长度，以便接收方知道后面有多少字节，这样您就不会受到流行为的影响。但更重要的是，通过套接字在线程之间交换数据是一种非常避免使用带互斥锁的数组的昂贵方法。线程可以不受限制地访问进程中的内存，您不需要进程间通信机制来让它们交换数据。

关于c++ - 如果我不先创建 TCP 连接，为什么发送数据报不起作用？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5611213/