Environment: VC++ 6
Reading and Writing Files Directly
MFC’s and App Wizard’s built-in serialization capabilities are great if what you are doing is within defined parameters such as stream I/O. But what about an old-fashioned, powerful way of handling files like non-Windows programmers: creating, reading, and writing files directly? There is some nifty code on Code Guru that addresses this issue via custom functions; however, there is a simple, old-fashioned way of handling file I/O at a lower level, and it’s VERY powerful!
The MFC Library has the CFile class. Here are the Member Functions of the CFile Class:
| Member Function | Description |
| CFile | Creates the CFile object. If passed a filename, it opens the file. |
| Destructor | Cleans up a CFile object that’s going out of scope. If the file is open, it closes that file. |
| Abort() | Immediately closes the file with no regard for errors. |
| Close() | Closes the file. |
| Duplicate() | Creates a duplicate file object. |
| Flush() | Flushes data from the stream. |
| GetFileName() | Gets the file’s filename. |
| GetFilePath() | Gets the file’s full path. |
| GetFileTitle() | Gets the file’s title (the filename without the extension). |
| GetLength() | Gets the file’s length. |
| GetPosition() | Gets the current position within the file. |
| GetStatus() | Gets the file’s status. |
| LockRange() | Locks a portion of the file. |
| Open() | Opens the file. |
| Read() | Reads data from the file. |
| Remove() | Deletes a file. |
| Rename() | Renames the file. |
| Seek() | Sets the position within the file. |
| SeekToBegin() | Sets the position to the beginning of the file. |
| SeekToEnd() | Sets the position to the end of the file. |
| SetFilePath() | Sets the file’s path. |
| SetLength() | Sets the file’s length. |
| SetStatus() | Sets the file’s status. |
| UnlockRange() | Unlocks a portion of the file. |
| Write() | Writes data to the file. |
As you can see, the CFile class offers real file-handling power. Here is some practical sample code to demonstrate the use of the CFile class. This creates and opens a file, and writes a string to it:
// Create the file to Write to.
CFile file(“TESTFILE.TXT”, CFile::modeCreate |
CFile::modeWrite);
// Write data to the file.
CString message(“Hello World!”);
int length = message.GetLength();
file.Write((LPCTSTR)message, length);
Reading from a file isn’t much different than writing to one:
// Open the file to Read from.
CFile file(“TESTFILE.TXT”, CFile::modeRead);
// Read data from the file.
char s[81];
int bytesRead = file.Read(s, 80);
s[bytesRead] = 0;
CString message = s;
These examples use hard-coded filenames. For a more pleasurable user experience, and to add a nice touch to your programs, use the MFC class CFileDialog (in the online help).