#include <windows.h>
int main(int argc, char **argv) {
 int returncode;
 long written;
 DCB dcb = {0};
 dcb.DCBlength = sizeof(DCB);
 HANDLE commport = NULL;
 HANDLE logfile = NULL;
 commport = CreateFile("COM1", GENERIC_READ | GENERIC_WRITE,
  0, 0, OPEN_EXISTING, 0, 0);
 logfile = CreateFileW(L"\\Temp\\sendcom.log", GENERIC_WRITE,
  0, 0, CREATE_ALWAYS, 0, 0);
 if (!(commport == INVALID_HANDLE_VALUE)) {
  if (GetCommState(commport, &dcb)) {
   WriteFile(logfile, &dcb, sizeof(DCB), &written, NULL);
   dcb.BaudRate = CBR_9600;
   dcb.ByteSize = 8;
   dcb.Parity = NOPARITY;
   dcb.StopBits = ONESTOPBIT;
   // disable all hardware handshaking, parity, flow control
   dcb.fParity = FALSE;
   dcb.fOutX = FALSE;
   dcb.fInX = FALSE;
   dcb.fRtsControl = RTS_CONTROL_DISABLE;
   dcb.fDtrControl = DTR_CONTROL_DISABLE;
   dcb.fOutxCtsFlow = FALSE;
   dcb.fOutxDsrFlow = FALSE;
   dcb.fAbortOnError = FALSE;  // would require more coding if TRUE
   if (SetCommState(commport, &dcb)) {
    printf("Writing %s to COM1\n", argv[1]);
    // for debugging, change handle to STD_OUTPUT_HANDLE (works OK that way)
    //commport = GetStdHandle(STD_OUTPUT_HANDLE);
    if (WriteFile(commport, argv[1], strlen(argv[1]), &written, NULL)) {
     returncode = 0;
    } else {
     printf("Failed, Windows error number is %d\n", GetLastError());
     returncode = 1;
    }
   } else {
    returncode = 2;
   }
  } else {  // GetCommState() failed
   returncode = 3;
  }
 } else {
  printf("invalid commport handle: 0x%x\n", commport);
  returncode = 4;
 }
 CloseHandle(commport);
 return returncode;
}