Configuring a Communications Resource

The following example opens a handle to COM2 and fills in a DCB structure with the current configuration. The DCB structure is then modified and used to reconfigure the device.

#include <windows.h>
#include <tchar.h>
#include <stdio.h>

void PrintCommState(DCB dcb)
{
 // Print some of the DCB structure values
 _tprintf( TEXT("\nBaudRate = %d, ByteSize = %d, Parity = %d, StopBits = %d\n"), 
 dcb.BaudRate, 
 dcb.ByteSize, 
 dcb.Parity,
 dcb.StopBits );
}


int _tmain( int argc, TCHAR *argv[] )
{
 DCB dcb;
 HANDLE hCom;
 BOOL fSuccess;
 TCHAR *pcCommPort = TEXT("COM1"); // Most systems have a COM1 port

 // Open a handle to the specified com port.
 hCom = CreateFile( pcCommPort,
 GENERIC_READ | GENERIC_WRITE,
 0, // must be opened with exclusive-access
 NULL, // default security attributes
 OPEN_EXISTING, // 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);
 }

 // Initialize the DCB structure.
 SecureZeroMemory(&dcb, sizeof(DCB));
 dcb.DCBlength = sizeof(DCB);

 // Build on the current configuration by first retrieving all current
 // settings.
 fSuccess = GetCommState(hCom, &dcb);

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

 PrintCommState(dcb); // Output to console

 // Fill in some DCB values and set the com state: 
 // 57,600 bps, 8 data bits, no parity, and 1 stop bit.
 dcb.BaudRate = CBR_57600; // baud rate
 dcb.ByteSize = 8; // data size, xmit and rcv
 dcb.Parity = NOPARITY; // parity bit
 dcb.StopBits = ONESTOPBIT; // stop bit

 fSuccess = SetCommState(hCom, &dcb);

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

 // Get the comm config again.
 fSuccess = GetCommState(hCom, &dcb);

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

 PrintCommState(dcb); // Output to console

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