用C语言写一段上位机如何实现自动连接

实现自动连接需要使用串口通信。下面是一段基于Windows系统的C语言代码示例：

#include <windows.h>

HANDLE hSerial;
DCB dcbSerialParams = {0};
COMMTIMEOUTS timeouts = {0};

int main()
{
    // 打开串口
    hSerial = CreateFile("COM1", GENERIC_READ | GENERIC_WRITE, 0, NULL,
                         OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if(hSerial == INVALID_HANDLE_VALUE)
    {
        printf("无法打开串口\n");
        return 1;
    }

    // 配置串口
    dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
    if(!GetCommState(hSerial, &dcbSerialParams))
    {
        printf("无法获取串口配置\n");
        CloseHandle(hSerial);
        return 1;
    }
    dcbSerialParams.BaudRate = CBR_9600;
    dcbSerialParams.ByteSize = 8;
    dcbSerialParams.StopBits = ONESTOPBIT;
    dcbSerialParams.Parity = NOPARITY;
    if(!SetCommState(hSerial, &dcbSerialParams))
    {
        printf("无法配置串口\n");
        CloseHandle(hSerial);
        return 1;
    }

    // 设置读取超时
    timeouts.ReadIntervalTimeout = 50;
    timeouts.ReadTotalTimeoutConstant = 50;
    timeouts.ReadTotalTimeoutMultiplier = 10;
    timeouts.WriteTotalTimeoutConstant = 50;
    timeouts.WriteTotalTimeoutMultiplier = 10;
    if(!SetCommTimeouts(hSerial, &timeouts))
    {
        printf("无法设置读取超时\n");
        CloseHandle(hSerial);
        return 1;
    }

    // 尝试连接
    int connected = 0;
    for(int i = 0; i < 10; i++)
    {
        char buf[100];
        DWORD bytesRead;
        if(!ReadFile(hSerial, buf, sizeof(buf), &bytesRead, NULL))
        {
            printf("读取数据失败\n");
            CloseHandle(hSerial);
            return 1;
        }
        if(bytesRead > 0)
        {
            connected = 1;
            break;
        }
        Sleep(1000);
    }

    if(connected)
    {
        printf("连接成功\n");
    }
    else
    {
        printf("连接失败\n");
    }

    // 关闭串口
    CloseHandle(hSerial);
    return 0;
}

该代码打开了串口COM1，配置波特率为9600，数据位为8位，停止位为1位，无校验位，并设置了读取超时。然后尝试从串口读取数据来判断是否连接成功。如果连续10次读取都没有收到数据，则认为连接失败。