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Just call CreateFile, ReadFile and WriteFile. The docs on CreateFile specify how ports should be opened, and I suppose reading/writing COM ports is the same as reading/writing normal files.

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I think you''ve mistitled your question. It''s too easy to read COM as "Component Object" rather than "Serial Communications Port" - at any rate - here''s some code for you.


// From the book "Win32 System Services: The Heart of Windows 98

// and Windows 2000"

// by Marshall Brain

// Published by Prentice Hall


// Copyright 1995, by Prentice Hall.


// This code demonstrates an extremely simple serial connection.


// commtest.cpp

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

void ErrorHandler(char *s, DWORD err)
fprintf(stderr,"%s\n", s);
fprintf(stderr,"Error number: %s\n", err);

void main()

HANDLE comHandle;
BOOL success;
DCB dcb;
char str[100];
DWORD numWrite, numRead;

// Open the comm port. Can open COM, LPT,

// or \\\\.\\TELNET

comHandle = CreateFile("COM2"
, 0, 0
, 0);

if ( comHandle == INVALID_HANDLE_VALUE ) {
ErrorHandler("In CreateFile", GetLastError());

// Get the current settings of the COMM port

success = GetCommState(comHandle, &dcb);

if ( !success ) {
ErrorHandler("In GetCommState", GetLastError());

// Modify the baud rate, etc.

dcb.BaudRate = 2400;
dcb.ByteSize = 8;
dcb.Parity = NOPARITY;
dcb.StopBits = ONESTOPBIT;

// Apply the new comm port settings

success = SetCommState(comHandle, &dcb);
if ( !success ) {
ErrorHandler("In SetCommState", GetLastError());

// Change the ReadIntervalTimeout so that

// ReadFile will return immediately. See

// help file

timeouts.ReadIntervalTimeout = MAXDWORD;
timeouts.ReadTotalTimeoutMultiplier = 0;
timeouts.ReadTotalTimeoutConstant = 0;
timeouts.WriteTotalTimeoutMultiplier = 0;
timeouts.WriteTotalTimeoutConstant = 0;
SetCommTimeouts( comHandle, &timeouts );

// Set the Data Terminal Ready line

EscapeCommFunction(comHandle, SETDTR);

// Send an "at" command to the modem

// Be sure to use \r rather than \n

strcpy(str, "at\r");
success = WriteFile(comHandle
, str
, strlen(str)
, &numWrite
, 0);

if ( !success ) {
ErrorHandler("In WriteFile", GetLastError());

// Wait 2 seconds and then retrieve from the

// modem


success = ReadFile(comHandle, str, 100, &numRead, 0);

if ( !success ) {
ErrorHandler("In ReadFile", GetLastError());

// Print the string received

fprintf(stdout,"%d\n", numRead);
fprintf(stdout, "%s\n", str);

// Clear the DTR line

EscapeCommFunction(comHandle, CLRDTR);



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