C语言使用UDP协议监听指定端口1，当监听到端口1时，使用端口2转发到192.168.1.100的100端口上，并监听端口2，当监听到端口2时，将数据转发回给端口1

在C语言中，可以使用Socket编程来实现UDP协议的监听和转发功能。以下是一个简单的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>

#define PORT1 1
#define PORT2 2
#define SERVER_IP "192.168.1.100"
#define SERVER_PORT 100

int main() {
    int sockfd1, sockfd2;
    struct sockaddr_in server_addr, client_addr;
    socklen_t addr_len = sizeof(struct sockaddr_in);
    char buffer[1024];

    // 创建socket1
    if ((sockfd1 = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
        perror("socket1 creation failed");
        exit(1);
    }

    // 绑定socket1到指定端口
    memset(&client_addr, 0, sizeof(client_addr));
    client_addr.sin_family = AF_INET;
    client_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    client_addr.sin_port = htons(PORT1);
    if (bind(sockfd1, (struct sockaddr *)&client_addr, sizeof(client_addr)) == -1) {
        perror("socket1 bind failed");
        exit(1);
    }

    // 创建socket2
    if ((sockfd2 = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
        perror("socket2 creation failed");
        exit(1);
    }

    // 绑定socket2到指定端口
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(PORT2);
    if (bind(sockfd2, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        perror("socket2 bind failed");
        exit(1);
    }

    while (1) {
        // 监听端口1，接收数据
        memset(buffer, 0, sizeof(buffer));
        if (recvfrom(sockfd1, buffer, sizeof(buffer), 0, (struct sockaddr *)&client_addr, &addr_len) == -1) {
            perror("receive from socket1 failed");
            exit(1);
        }

        // 打印接收到的数据
        printf("Received data: %s\n", buffer);

        // 将数据转发到目标服务器
        if (sendto(sockfd2, buffer, strlen(buffer), 0, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
            perror("send to socket2 failed");
            exit(1);
        }

        // 监听端口2，接收数据
        memset(buffer, 0, sizeof(buffer));
        if (recvfrom(sockfd2, buffer, sizeof(buffer), 0, (struct sockaddr *)&server_addr, &addr_len) == -1) {
            perror("receive from socket2 failed");
            exit(1);
        }

        // 打印接收到的数据
        printf("Received data: %s\n", buffer);

        // 将数据转发回端口1
        if (sendto(sockfd1, buffer, strlen(buffer), 0, (struct sockaddr *)&client_addr, sizeof(client_addr)) == -1) {
            perror("send to socket1 failed");
            exit(1);
        }
    }

    close(sockfd1);
    close(sockfd2);

    return 0;
}

请注意，这只是一个简单的示例，仅用于演示UDP监听和转发的基本原理。在实际应用中，可能需要对代码进行适当的修改和优化，以满足具体需求和安全性要求。