File I/O

This section covers the core Windows API functions for performing input and output operations on files. These functions allow applications to create, read, write, and manage files on the file system.

Core Concepts

Handles: File operations typically use handles, which are opaque identifiers representing an open file or device.
File Access Rights: Specify the permissions required to access a file (e.g., read, write, execute).
Sharing Modes: Define how other processes can access the file concurrently.
File Pointers: Keep track of the current position within a file for reading or writing.

Key Functions

Creating and Opening Files

These functions are used to create new files or open existing ones.

Function	Description
`CreateFile`	Creates or opens a file or I/O device. Returns a handle to the device.
`CreateFile2`	A more robust and flexible version of `CreateFile`, introduced in Windows 8.

Reading and Writing Data

Functions for transferring data between memory buffers and files.

Function	Description
`ReadFile`	Reads data from a file or I/O device into a buffer.
`WriteFile`	Writes data from a buffer to a file or I/O device.
`ReadFileEx`	Reads data from a file or I/O device into a buffer, using asynchronous I/O.
`WriteFileEx`	Writes data from a buffer to a file or I/O device, using asynchronous I/O.

Managing File Pointers

Functions to reposition the file pointer.

Function	Description
`SetFilePointer`	Moves the file pointer to a specified location.
`SetFilePointerEx`	A more robust version of `SetFilePointer` that supports 64-bit offsets.
`SeekFilePointer`	(Deprecated, use `SetFilePointerEx`) Moves the file pointer.

Closing Files

Releases the file handle and associated resources.

Function	Description
`CloseHandle`	Closes an open object handle, including file handles.

File Attributes and Information

Functions to retrieve or set file attributes and metadata.

Function	Description
`GetFileAttributes`	Retrieves the attributes for a specified file or directory.
`SetFileAttributes`	Sets the attributes for a specified file or directory.
`GetFileSizeEx`	Retrieves the size of the specified file.

Example: Basic File Writing


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

int main() {
    HANDLE hFile;
    DWORD dwBytesWritten;
    const char* message = "Hello, Windows API File I/O!";
    const char* filename = "example.txt";

    // Create or open the file
    hFile = CreateFile(filename,               // File name
                       GENERIC_WRITE,          // Write access
                       0,                      // No sharing
                       NULL,                   // Default security attributes
                       CREATE_ALWAYS,          // Overwrite if exists, create if not
                       FILE_ATTRIBUTE_NORMAL,  // Normal file
                       NULL);                  // No template file

    if (hFile == INVALID_HANDLE_VALUE) {
        printf("Error opening file (%d).\n", GetLastError());
        return 1;
    }

    // Write data to the file
    if (!WriteFile(hFile,          // Handle to file
                   message,        // Data to write
                   strlen(message),// Number of bytes to write
                   &dwBytesWritten,// Number of bytes written
                   NULL)) {        // Overlapped structure
        printf("Error writing to file (%d).\n", GetLastError());
        CloseHandle(hFile);
        return 1;
    }

    printf("%d bytes written successfully.\n", dwBytesWritten);

    // Close the file handle
    CloseHandle(hFile);
    printf("File closed.\n");

    return 0;
}

Note: For robust error handling, always check the return value of file I/O functions and use GetLastError() to retrieve specific error codes.

Warning: Using deprecated functions like SeekFilePointer is discouraged. Prefer modern alternatives like SetFilePointerEx for better compatibility and features.

Advanced Topics

Asynchronous I/O (Overlapped I/O) for non-blocking operations.
File mapping for efficient memory access to file contents.
Directory management functions (e.g., CreateDirectory, RemoveDirectory).
File locking for exclusive access.
Unicode vs. ANSI character sets and their impact on file operations.

Explore the links in the sidebar for more detailed documentation on specific functions and related topics.