用c语言写一段modbus tcp 通讯客户端程序

好的，我可以帮助你写一段modbus tcp 通讯客户端程序，下面是代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <winsock2.h>

#pragma comment(lib, "ws2_32.lib")

#define MAX_BUF_SIZE 1024

struct ModbusHeader {
    uint16_t transaction_id;
    uint16_t protocol_id;
    uint16_t length;
    uint8_t unit_id;
    uint8_t function_code;
};

int main(int argc, char* argv[]) {
    if (argc != 4) {
        printf("Usage: %s <server_ip> <port> <register_num>\n", argv[0]);
        return 1;
    }

    WSADATA wsaData;
    int result = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (result != 0) {
        printf("WSAStartup failed with error: %d\n", result);
        return 1;
    }

    char* server_ip = argv[1];
    uint16_t port = atoi(argv[2]);
    int register_num = atoi(argv[3]);

    SOCKET client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (client_socket == INVALID_SOCKET) {
        printf("socket failed with error: %d\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    struct sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(port);
    server_addr.sin_addr.s_addr = inet_addr(server_ip);

    if (connect(client_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)) == SOCKET_ERROR) {
        printf("connect failed with error: %d\n", WSAGetLastError());
        closesocket(client_socket);
        WSACleanup();
        return 1;
    }

    struct ModbusHeader request;
    request.transaction_id = htons(1);
    request.protocol_id = htons(0);
    request.length = htons(6);
    request.unit_id = 1;
    request.function_code = 3;

    char buf[MAX_BUF_SIZE] = {0};
    memcpy(buf, &request, sizeof(request));

    uint16_t start_address = 0;
    uint16_t quantity = register_num;
    memcpy(buf + sizeof(request), &start_address, sizeof(start_address));
    memcpy(buf + sizeof(request) + sizeof(start_address), &quantity, sizeof(quantity));

    int send_len = send(client_socket, buf, sizeof(request) + sizeof(start_address) + sizeof(quantity), 0);
    if (send_len == SOCKET_ERROR) {
        printf("send failed with error: %d\n", WSAGetLastError());
        closesocket(client_socket);
        WSACleanup();
        return 1;
    }

    int recv_len = recv(client_socket, buf, MAX_BUF_SIZE, 0);
    if (recv_len == SOCKET_ERROR) {
        printf("recv failed with error: %d\n", WSAGetLastError());
        closesocket(client_socket);
        WSACleanup();
        return 1;
    }

    uint8_t byte_count;
    memcpy(&byte_count, buf + sizeof(request), sizeof(byte_count));

    uint16_t register_data[128];
    memcpy(register_data, buf + sizeof(request) + sizeof(byte_count), byte_count);

    for (int i = 0; i < register_num; i++) {
        printf("Register[%d]: %d\n", i, ntohs(register_data[i]));
    }

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

这段代码实现了一个使用 modbus tcp 协议的客户端程序，可以获取指定数量的寄存器数据并打印出来。

注意，这段代码需要在 Windows 平台上编译运行，并且需要链接“ws2_32.lib”库。如果需要在其他平台上运行，可能需要进行一定的修改。