Configuring a Communications Resource

The following example opens a handle to COM1 and fills in a DCB structure with the current configuration. The DCB structure is then modified and used to reconfigure the device.

/* A sample program to illustrate setting up a serial port. */

#include <windows.h>

int
main(int argc, char *argv[])
{
  DCB dcb;
  HANDLE hCom;
  BOOL fSuccess;
  char *pcCommPort = "COM2";

  hCom = CreateFile( pcCommPort,
                     GENERIC_READ | GENERIC_WRITE,
                     0,    // comm devices must be opened w/exclusive-access
                     NULL, // no security attributes
                     OPEN_EXISTING, // comm devices must use OPEN_EXISTING
                     0,    // not overlapped I/O
                     NULL  // hTemplate must be NULL for comm devices
                     );

  if (hCom == INVALID_HANDLE_VALUE) {
      // Handle the error.
      printf ("CreateFile failed with error %d.\n", GetLastError());
      return (1);
    }

  // We will build on the current configuration, and skip setting the size
  // of the input and output buffers with SetupComm.

  fSuccess = GetCommState(hCom, &dcb);

  if (!fSuccess) {
      // Handle the error.
      printf ("GetCommState failed with error %d.\n", GetLastError());
      return (2);
    }

  // Fill in the DCB: baud=57,600 bps, 8 data bits, no parity, and 1 stop bit.

  dcb.BaudRate = CBR_57600;     // set the baud rate
  dcb.ByteSize = 8;             // data size, xmit, and rcv
  dcb.Parity = NOPARITY;        // no parity bit
  dcb.StopBits = ONESTOPBIT;    // one stop bit

  fSuccess = SetCommState(hCom, &dcb);

  if (!fSuccess) {
      // Handle the error.
      printf ("SetCommState failed with error %d.\n", GetLastError());
      return (3);
    }

  printf ("Serial port %s successfully reconfigured.\n", pcCommPort);
  return (0);
}