用c语言写一个简单的modbus tcp主站程序

好的，可以的。下面是一个示例代码：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<errno.h>
#include<unistd.h>
#include<sys/socket.h>
#include<arpa/inet.h>

#define SERVER_IP   "127.0.0.1"
#define SERVER_PORT 502
#define BUFFER_SIZE 1024

// Modbus TCP message header
typedef struct {
    uint16_t trans_id;  // Transaction ID
    uint16_t prot_id;   // Protocol ID (0x0000 for Modbus protocol)
    uint16_t length;   // Length of the message data following the header
    uint8_t device;    // Device ID (0xFF for Ethernet communications)
    uint8_t func_code; // Function code (0x01 for Read Coils function)
    uint16_t addr;     // Starting address of the coils to be read
    uint16_t qty;      // Quantity of coiles to be read
} mbtcp_header;

int main()
{
    int sockfd = 0;
    char buffer[BUFFER_SIZE];
    struct sockaddr_in serv_addr;
    mbtcp_header mbtcp;

    // Create a socket for the Modbus TCP connection
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        printf("Error: could not create socket. %s\n", strerror(errno));
        return -1;
    }

    // Specify the server address and port for the Modbus TCP connection
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr(SERVER_IP);
    serv_addr.sin_port = htons(SERVER_PORT);

    // Connect to the Modbus TCP server
    if (connect(sockfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0) {
        printf("Error: could not connect to server. %s\n", strerror(errno));
        return -1;
    }

    // Prepare a Modbus TCP message to read coils
    mbtcp.trans_id = rand() % 0xFFFF;    // Random transaction ID
    mbtcp.prot_id = 0x0000;              // Modbus protocol ID
    mbtcp.length = 0x0006;               // Message data length
    mbtcp.device = 0xFF;                 // Ethernet device ID
    mbtcp.func_code = 0x01;              // Read coils function code
    mbtcp.addr = htons(0x0000);          // Starting address of the coils to be read
    mbtcp.qty = htons(0x0008);           // Quantity of coils to be read

    // Send the Modbus TCP message
    if (send(sockfd, &mbtcp, sizeof(mbtcp), 0) < 0) {
        printf("Error: could not send message. %s\n", strerror(errno));
        return -1;
    }

    // Receive the Modbus TCP response
    if (recv(sockfd, buffer, BUFFER_SIZE, 0) < 0) {
        printf("Error: could not receive response. %s\n", strerror(errno));
        return -1;
    }

    // Close the Modbus TCP connection
    close(sockfd);

    return 0;
}

这是一个简单的示例程序，用于向 Modbus TCP 主站发送一个读取线圈的命令，然后接收 Modbus TCP 从站的响应。在实际使用中，还需要对命令和响应的格式进行具体的定制和解析。