c - 在 win32 UDP 套接字应用程序中无法从 UDP 服务器接收数据

Question

我有一个硬件 ARM 控件作为 UDP 服务器，我通过下面用 C# 编写的代码与其进行通信。 PC是UDP客户端。服务器只是回显数据。

这工作正常，没有任何问题，而且很稳定。

using System.Net.Sockets;
using System.Net;
using System.Text;
using System;

namespace UDPSocket
{
    class UDPSender
    {
        static void Main(string[] args)
        {
            UInt32 i=0;
            Int32 PORT = 45555;
            for (; i < 15; )
            {
                Console.WriteLine(i++);
                Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram,
                    ProtocolType.Udp);

                IPAddress broadcast = IPAddress.Parse("192.168.0.10");

                byte[] sendbuf = Encoding.ASCII.GetBytes("Shriganesh Damle, Infineon Techonologies India Pvt Ltd, Bangalore");
                IPEndPoint ep = new IPEndPoint(broadcast, PORT);

                //Creates a UdpClient for reading incoming data.
                UdpClient receivingUdpClient = new UdpClient(PORT);

                s.SendTo(sendbuf, ep);

                Console.WriteLine("Message sent to the broadcast address");

                //Creates an IPEndPoint to record the IP Address and port number of the sender.  
                // The IPEndPoint will allow you to read datagrams sent from any source.
                IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);

                // Blocks until a message returns on this socket from a remote host.
                Byte[] receiveBytes = receivingUdpClient.Receive(ref RemoteIpEndPoint);

                string returnData = Encoding.ASCII.GetString(receiveBytes);

                Console.WriteLine("This is the message you received " +
                                            returnData.ToString());
                Console.WriteLine("This message was sent from " +
                                            RemoteIpEndPoint.Address.ToString() +
                                            " on their port number " +
                                            RemoteIpEndPoint.Port.ToString());
                //Console.Read();
                receivingUdpClient.Close();
            }
            Console.Read();
        }
    }
}

现在，我想要在 Win32 C 应用程序中使用相同的 PC 代码。我尝试了下面的代码。

/*
    Simple udp client    
*/
#include<stdio.h>
#include<winsock2.h>

#pragma comment(lib,"ws2_32.lib") //Winsock Library

#define SERVER "192.168.0.10"  //ip address of udp server
#define BUFLEN 512  //Max length of buffer
#define PORT 45555   //The port on which to listen for incoming data

int main(void)
{
    struct sockaddr_in si_other;
    int s, slen=sizeof(si_other);
    char buf[BUFLEN];
    char message[BUFLEN];
    WSADATA wsa;

    //Initialise winsock
    printf("\nInitialising Winsock...");
    if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
    {
        printf("Failed. Error Code : %d",WSAGetLastError());
        exit(EXIT_FAILURE);
    }
    printf("Initialised.\n");

    //create socket
    if ( (s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == SOCKET_ERROR)
    {
        printf("socket() failed with error code : %d" , WSAGetLastError());
        exit(EXIT_FAILURE);
    }

    //setup address structure
    memset((char *) &si_other, 0, sizeof(si_other));
    si_other.sin_family = AF_INET;
    si_other.sin_port = htons(PORT);
    si_other.sin_addr.S_un.S_addr = inet_addr(SERVER);

    //start communication
    while(1)
    {
        printf("Enter message : ");
        gets(message);

        //send the message
        if (sendto(s, message, strlen(message) , 0 , (struct sockaddr *) &si_other, slen) == SOCKET_ERROR)
        {
            printf("sendto() failed with error code : %d" , WSAGetLastError());
            exit(EXIT_FAILURE);
        }

        //receive a reply and print it
        //clear the buffer by filling null, it might have previously received data
        memset(buf,'\0', BUFLEN);
        //try to receive some data, this is a blocking call
        if (recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *) &si_other, &slen) == SOCKET_ERROR)
        {
            printf("recvfrom() failed with error code : %d" , WSAGetLastError());
            exit(EXIT_FAILURE);
        }

        puts(buf);
    }

    closesocket(s);
    WSACleanup();

    return 0;
}

此代码能够发送到 UDP 服务器并回显。但是recvfrom调用将等待数据直到无限时间。 recvfrom 正在阻塞调用。我给出了正确的 IP 地址和端口。我仍然无法在 Win32 应用程序中从服务器接收数据。你能帮忙吗？

Answer 1

如果要在套接字上接收数据，则需要将其绑定(bind)到一个或多个本地地址和本地端口。您的 C# 版本通过 new UdpClient(PORT) 实现此目的(请注意 PORT 参数)，但您的 C 版本不会执行任何类似操作。

创建套接字后，执行以下操作

sockaddr_in localAddr;

localAddr.sin_family = AF_INET;
localAddr.sin_port = htons(PORT);
localAddr.sin_addr.S_un.S_addr = INADDR_ANY;

bind(s, &localAddr, sizeof(sockaddr_in));

并验证它是否返回 0 以指示成功。

或者，如果您创建第二个套接字来接收服务器响应，C 版本将与 C# 版本更加并行。我认为没有必要在 C 中执行此操作(更准确地说，在 Winsock2 中)，但使用相同的套接字发送和接收可能需要绑定(bind)到特定的本地地址而不是 INADDR_ANY。