Windows API Reference

Introduction to I/O Devices

The Windows operating system provides a comprehensive set of APIs for interacting with various input/output (I/O) devices. These APIs allow applications to communicate with hardware such as disks, keyboards, mice, printers, network adapters, and specialized peripherals.

Understanding how to manage and utilize I/O devices is crucial for developing robust and efficient Windows applications. This section covers the fundamental concepts and key APIs related to device management, data transfer, and error handling.

Key Concepts

Device Drivers: Software components that translate generic I/O requests from the operating system into specific commands for hardware devices.
I/O Request Packets (IRPs): Structures used by the operating system to communicate I/O operations to device drivers.
File Handles: Abstract representations of open devices or files, used to perform I/O operations.
Input/Output Control (IOCTL): A mechanism for applications to send custom commands directly to device drivers.
Asynchronous I/O: Allows an application to initiate an I/O operation and continue processing without waiting for the operation to complete.

Core APIs

The following Win32 APIs are fundamental for working with I/O devices:

Device Management

CreateFile: Opens an existing file or creates a new file. It can also open existing devices, specify desired access, and share modes.
CloseHandle: Closes an open object handle, such as a file or device handle.
DeviceIoControl: Sends a custom control code directly to a specified device driver, allowing for device-specific operations.
SetupDiGetDeviceInterfaceList, SetupDiEnumDeviceInfo, SetupDiGetDeviceRegistryProperty: APIs for enumerating devices and retrieving their properties.

Data Transfer

ReadFile: Reads data from a file or device.
WriteFile: Writes data to a file or device.
ReadFileEx, WriteFileEx: Asynchronous versions of ReadFile and WriteFile, which use I/O completion routines.

Error Handling

GetLastError: Retrieves the last error code set by a function. Common error codes for I/O operations include ERROR_IO_PENDING (for asynchronous operations), ERROR_FILE_NOT_FOUND, and ERROR_DEVICE_DOES_NOT_EXIST.

Important Note on Device Access

Accessing raw hardware devices often requires administrative privileges. Applications designed for general users should typically interact with devices through higher-level abstractions like file system APIs or COM interfaces rather than directly manipulating device drivers.

Example: Reading from a Serial Port

This example demonstrates a simplified approach to reading data from a serial port using CreateFile and ReadFile.


#include <windows.h>
#include <iostream>

int main() {
    HANDLE hSerial = CreateFile(
        L"\\\\.\\COM1",       // Port name
        GENERIC_READ | GENERIC_WRITE, // Read and write access
        0,                    // No sharing
        NULL,                 // Default security attributes
        OPEN_EXISTING,        // Open only if it exists
        FILE_ATTRIBUTE_NORMAL,// Normal file attributes
        NULL                  // No template file
    );

    if (hSerial == INVALID_HANDLE_VALUE) {
        std::cerr << "Error opening serial port: " << GetLastError() << std::endl;
        return 1;
    }

    std::cout << "Serial port opened successfully." << std::endl;

    // Configuration (omitted for brevity, involves GetCommState, SetCommState, etc.)

    BYTE buffer[256];
    DWORD bytesRead;

    // Example read operation
    if (ReadFile(hSerial, buffer, sizeof(buffer) - 1, &bytesRead, NULL)) {
        buffer[bytesRead] = '\0'; // Null-terminate the string
        std::cout << "Read " << bytesRead << " bytes: " << buffer << std::endl;
    } else {
        std::cerr << "Error reading from serial port: " << GetLastError() << std::endl;
    }

    CloseHandle(hSerial);
    std::cout << "Serial port closed." << std::endl;

    return 0;
}