C++ UDP客户端/套接字编程：无法发送和接收

Question

第一次在这里。我正在尝试实施一个UDP套接字客户机/服务器，以便与BGI一起为我的大学考试工作。我想发送移动坐标并接收测试字符。但是，当我使用recvfrom（）它不起作用，没有它工作正常。对不起我的英语。

这里的客户端文件：

#define WIN32_LEAN_AND_MEAN 

#include<winsock2.h> 
#include<windows.h> 
#include<string> 
#include<stdio.h> 
#include<stdlib.h> 
#include<iostream> 
#include<graphics.h> 

#define SIZE 512 
#define PORT 20252 
#define SERVER_IP "127.0.0.1" 
#define CLIENT_IP "127.0.0.1" 

using namespace std; 

int main() { 
    WSADATA wsaData; 
    SOCKET ClientSocket; 
    int server_length; 
    struct sockaddr_in server; 
    struct sockaddr_in client; 
    char print_buffer[SIZE]; 
    /* ==================================================================================*/ 
    WSAStartup(0x0101, &wsaData); 
    ClientSocket = socket(AF_INET, SOCK_DGRAM, 0); 
    memset((void *)&server, '\0', sizeof(struct sockaddr_in)); 
    memset((void *)&client, '\0', sizeof(struct sockaddr_in)); 
    server.sin_family  = AF_INET; 
    server.sin_port  = htons(PORT); 
    server.sin_addr.s_addr = inet_addr(SERVER_IP); 
    client.sin_family  = AF_INET; 
    client.sin_port  = htons(PORT); 
    client.sin_addr.s_addr = inet_addr(CLIENT_IP); 
    bind(ClientSocket, (struct sockaddr *)&client, sizeof(struct sockaddr_in)); 
    /* ==================================================================================*/ 

    int x = 0; 

    while (x != 1) { 
     server_length = sizeof(struct sockaddr_in); 

     if (GetKeyState(VK_RIGHT)&0x80) { 
      char send_right_P1[SIZE] = "P1RIGHT\r\n"; 
      sendto(ClientSocket, send_right_P1, (int)strlen(send_right_P1) + 1, 0, (struct sockaddr *)&server, server_length); 
      memset(&send_right_P1[0], 0, sizeof(send_right_P1)); 
     } 
     if (GetKeyState(VK_LEFT)&0x80) { 
      char send_left_P1[SIZE] = "P1LEFT\r\n"; 
      sendto(ClientSocket, send_left_P1, (int)strlen(send_left_P1) + 1, 0, (struct sockaddr *)&server, server_length); 
      memset(&send_left_P1[0], 0, sizeof(send_left_P1)); 
     } 
     if (GetKeyState(VK_UP)&0x80) { 
      char send_up_P1[SIZE] = "P1UP\r\n"; 
      sendto(ClientSocket, send_up_P1, (int)strlen(send_up_P1) + 1, 0, (struct sockaddr *)&server, server_length); 
      memset(&send_up_P1[0], 0, sizeof(send_up_P1)); 
     } 
     if (GetKeyState(VK_DOWN)&0x80) { 
      char send_down_P1[SIZE] = "P1DOWN\r\n"; 
      sendto(ClientSocket, send_down_P1, (int)strlen(send_down_P1) + 1, 0, (struct sockaddr *)&server, server_length); 
      memset(&send_down_P1[0], 0, sizeof(send_down_P1)); 
     } 
     if (GetKeyState(VK_ESCAPE)&0x80) { 
      char send_escape[SIZE] = "ESCAPE\r\n"; 
      sendto(ClientSocket, send_escape, (int)strlen(send_escape) + 1, 0, (struct sockaddr *)&server, server_length); 
      memset(&send_escape[0], 0, sizeof(send_escape)); 
     } 

     recvfrom(ClientSocket, print_buffer, SIZE, 0, (struct sockaddr *)&server, &server_length); 

     if (strcmp(print_buffer, "TESTE\r\n") == 0) { 
      cout << print_buffer; 
     } else cout << "Failed\n"; 

     memset(&print_buffer[0], 0, sizeof(print_buffer)); 

     delay(50); 

    } 

    closesocket(ClientSocket); 
    WSACleanup(); 
    return 0; 
} 

这里的服务器：

#define WIN32_LEAN_AND_MEAN 

#include<winsock2.h> 
#include<windows.h> 
#include<string> 
#include<stdio.h> 
#include<stdlib.h> 
#include<iostream> 
#include<graphics.h> 

#include "images.h" 

#define SIZE 512 
#define PORT 20252 
#define SERVER_IP "127.0.0.1" 
#define CLIENT_IP "127.0.0.1" 

using namespace std; 

int main() { 
    WSADATA wsaData; 
    SOCKET ServerSocket; 
    int client_length; 
    struct sockaddr_in server; 
    struct sockaddr_in client; 
    char Player1_Buffer[SIZE]; 
    /* ==================================================================================*/ 
    initwindow(800, 600); 

    int pg = 2, passo = 5, fim = 0; 

    GetImages(); 

    int Pos1X = 200, Pos1Y = 300, direction1 = 1; 
    int Pos2X = 600, Pos2Y = 300, direction2 = 1; 
    /* ==================================================================================*/ 
    WSAStartup(0x0101, &wsaData); 
    ServerSocket = socket(AF_INET, SOCK_DGRAM, 0); 
    memset((void *)&server, '\0', sizeof(struct sockaddr_in)); 
    memset((void *)&client, '\0', sizeof(struct sockaddr_in)); 
    server.sin_family  = AF_INET; 
    server.sin_port  = htons(PORT); 
    server.sin_addr.s_addr = inet_addr(SERVER_IP); 
    client.sin_family  = AF_INET; 
    client.sin_port  = htons(PORT); 
    client.sin_addr.s_addr = inet_addr(CLIENT_IP); 
    bind(ServerSocket, (struct sockaddr *)&server, sizeof(struct sockaddr_in)); 
    printf("Server running on %u.%u.%u.%u\n", (unsigned char)server.sin_addr.S_un.S_un_b.s_b1, 
               (unsigned char)server.sin_addr.S_un.S_un_b.s_b2, 
               (unsigned char)server.sin_addr.S_un.S_un_b.s_b3, 
               (unsigned char)server.sin_addr.S_un.S_un_b.s_b4); 
    printf("Press CTRL + C to quit\n"); 

    while (fim != 1) { 

     if (pg == 1) pg = 2; else pg = 1; 
     setactivepage(pg); 
     cleardevice(); 

     putimage(0, 0, background, OR_PUT); 

     drawBoy(Pos1X, Pos1Y, direction1); 

     setvisualpage(pg); 
     delay(50); 

     client_length = (int)sizeof(struct sockaddr_in); 
     recvfrom(ServerSocket, Player1_Buffer, SIZE, 0, (struct sockaddr *)&client, &client_length); 

     if (strcmp(Player1_Buffer, "P1RIGHT\r\n") == 0) { 
      Pos1X = Pos1X + passo; 
      direction1 = 3; 
      cout << "Received from Player1: " << Player1_Buffer << endl; 
     } 
     if (strcmp(Player1_Buffer, "P1LEFT\r\n") == 0) { 
      Pos1X = Pos1X - passo; 
      direction1 = 4; 
      cout << "Received from Player1: " << Player1_Buffer << endl; 
     } 
     if (strcmp(Player1_Buffer, "P1UP\r\n" ) == 0) { 
      Pos1Y = Pos1Y - passo; 
      direction1 = 2; 
      cout << "Received from Player1: " << Player1_Buffer << endl; 
     } 
     if (strcmp(Player1_Buffer, "P1DOWN\r\n") == 0) { 
      Pos1Y = Pos1Y + passo; 
      direction1 = 1; 
      cout << "Received from Player1: " << Player1_Buffer << endl; 
      char print_buffer[SIZE] = "TESTE\r\n"; 
      sendto(ServerSocket, print_buffer, (int)strlen(print_buffer) + 1, 0, (struct sockaddr *)&client, client_length); 
     } 
     if (strcmp(Player1_Buffer, "ESCAPE\r\n") == 0) { 
      fim = 1; 
      cout << "Received from Player1: " << Player1_Buffer << endl; 
     } 
    } 
    closesocket(ServerSocket); 
    WSACleanup(); 
    return 0; 
} 

Answer 1

做客户端上没有bind()插座。您将客户端套接字绑定到127.0.0.1:20252，然后将数据发送到相同的地址：端口对。

只需在客户端代码中删除对bind()的呼叫。

另一个选项（也在客户端上）是绑定到端口0，端口0将分配一个未使用的端口。

另请参见：检查bind(),sendto(),recvfrom()等的返回值，如果失败则显示错误代码。

再一次：recvfrom()的长度参数必须在调用之前初始化。例如，在客户端你应该这样做：

server_length = sizeof(server); 
recvfrom(ClientSocket, print_buffer, SIZE, 0, (struct sockaddr *)&server, &server_length); 

同样在服务器端。