Read Serial port on Windows

serial_port.c

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
 
int main() {
    const char reboot = 'R';
    const char ack = 6;
    HANDLE hSerial = NULL;
    DCB dcbSerialParams = {0};
    COMMTIMEOUTS timeouts = {0};
    DWORD bytes_written = 0;
    DWORD bytes_read = 0;
    BOOL status = FALSE;
    char buffer = 0;
         
    fprintf(stderr, "Opening serial port...");
    hSerial = CreateFile("\\\\.\\COM1", GENERIC_READ|GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hSerial == INVALID_HANDLE_VALUE) {
            fprintf(stderr, "Error: Could not open serial port.\n");
            return EXIT_FAILURE;
    } else {
        fprintf(stderr, "OK\n");
    }
     
    dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
    if (GetCommState(hSerial, &dcbSerialParams) == 0) {
        fprintf(stderr, "Error getting device state\n");
        CloseHandle(hSerial);
        return EXIT_FAILURE;
    }
     
    dcbSerialParams.BaudRate = CBR_115200;
    dcbSerialParams.ByteSize = 8;
    dcbSerialParams.StopBits = ONESTOPBIT;
    dcbSerialParams.Parity = NOPARITY;
    if(SetCommState(hSerial, &dcbSerialParams) == 0) {
        fprintf(stderr, "Error setting device parameters\n");
        CloseHandle(hSerial);
        return EXIT_FAILURE;
    }
 
    timeouts.ReadIntervalTimeout = 50;
    timeouts.ReadTotalTimeoutConstant = 50;
    timeouts.ReadTotalTimeoutMultiplier = 10;
    timeouts.WriteTotalTimeoutConstant = 50;
    timeouts.WriteTotalTimeoutMultiplier = 10;
    if(SetCommTimeouts(hSerial, &timeouts) == 0) {
        fprintf(stderr, "Error setting timeouts\n");
        CloseHandle(hSerial);
        return EXIT_FAILURE;
    }
    
    do {
        status = ReadFile(hSerial, &buffer, sizeof(buffer), &bytes_read, NULL);
        if (!status) {
            fprintf(stderr, "Error: Could not read serial port.\n");
            CloseHandle(hSerial);
            return EXIT_FAILURE;
        }
    } while (read_buffer != reboot);
    
    fprintf(stderr, "Sending ACK...");
    if(!WriteFile(hSerial, &ack, 1, &bytes_written, NULL)) {
        fprintf(stderr, "Error: Could not send ACK.\n");
        CloseHandle(hSerial);
        return EXIT_FAILURE;
    }   
     
    fprintf(stderr, "Closing serial port...");
    if (CloseHandle(hSerial) == 0) {
        fprintf(stderr, "Error: Could not close serial port.\n");
        return EXIT_FAILURE;
    }
    fprintf(stderr, "OK\n");
    
    status = ExitWindowsEx(EWX_REBOOT, 0);
    if (!status) {
        fprintf(stderr, "Error: Could not reboot the system.\n");
        return EXIT_FAILURE;
    }
 
    return EXIT_SUCCESS;
}

Very useful, I modified by eliminating the loop. The variable read_buffer was not declared.It served me perfect for reading the weight of a truck scale. Thank you very much.