Files and I/O API Reference

Core Concepts

Understanding the fundamental concepts behind file and I/O operations in Windows is crucial for effective programming. This includes:

• File Handles: Unique identifiers returned by the system when a file is opened.
• I/O Buffering: Strategies for managing data transfer between applications and storage devices.
• Asynchronous I/O: Techniques for performing I/O operations without blocking the calling thread.
• File Attributes and Permissions: Properties associated with files and directories, controlling access.

Key Functions

File Creation and Opening

Functions to create new files or open existing ones.

• CreateFile: Opens or creates a file or device.
• OpenFile: Opens an existing file.

File Reading and Writing

Functions for reading data from and writing data to files.

• ReadFile: Reads data from a file or I/O device.
• WriteFile: Writes data to a file or I/O device.
• ReadFileEx: Reads data from a file or device asynchronously.
• WriteFileEx: Writes data to a file or device asynchronously.

File Positioning

Functions to set and get the current file position.

• SetFilePointer: Moves or obtains the current read/write pointer of a file.
• GetFileSizeEx: Retrieves the size of a file.

File Closing and Management

Functions to close file handles and manage file information.

• CloseHandle: Closes an open object handle.
• FlushFileBuffers: Forces buffered data to be written to a specified file.
• GetFileInformationByHandle: Retrieves detailed information about a file.

Directory Operations

Functions for creating, deleting, and enumerating directories.

• CreateDirectory: Creates a directory.
• RemoveDirectory: Deletes an empty directory.
• FindFirstFile: Retrieves information about the first file or directory in a specified path.
• FindNextFile: Retrieves information about the next file or directory.
• FindClose: Closes a file search handle.

Common Data Structures

Essential structures used with file and I/O functions:

• OVERLAPPED: Structure used for asynchronous I/O operations.
• WIN32_FIND_DATA: Structure containing information about a found file or directory.
• FILE_STANDARD_INFO: Structure containing standard file information.

Error Handling

Most I/O operations can fail. It's crucial to check the return values of API functions and use GetLastError to retrieve detailed error information.

DWORD errorCode = GetLastError();
if (errorCode != ERROR_SUCCESS) {
    // Handle the error
    LPTSTR errorMessage = NULL;
    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        errorCode,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR)&errorMessage,
        0,
        NULL);
    // Display or log errorMessage
    LocalFree(errorMessage);
}