Win32 | Steven Engelhardt

C++ c++ win32

Published: 2005-09-09

This is covered by any halfway-decent C++ book, but I believe it deserves reiteration: Use the RAII idiom. I don’t think I could explain RAII any better than HackCraft does in The RAII Programming Idiom.

Let me demonstrate how to use RAII with a semi-contrived example. Here’s the pre-RAII code:

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HMODULE hm = LoadLibrary(_T("user32.dll"));
if (hm != NULL) {
    FARPROC proc = GetProcAddress(hm, "MessageBoxW");
    if (proc != NULL) {
        typedef int (WINAPI *FnMessageBoxW)(HWND, LPCWSTR, LPCWSTR, UINT);FnMessageBoxW fnMessageBoxW = (FnMessageBoxW) proc;
        fnMessageBoxW(NULL, L"Hello World!", L"Hello World", MB_OK);
    }
    FreeLibrary(hm);
}

In this case, the resource wrapped is HMODULE, the resource acquisition function is LoadLibrary(), and the resource release function is FreeLibrary(). Beware of resources which have multiple resource release functions, such as Win32’s HANDLE with FindClose() and CloseHandle(); for these cases you will typically have to write multiple RAII classes. I will call the wrapper class HModule. Here’s how its use will look:

Win32 c mfc win32

Published: 2005-09-08

Beware File Open/Save Dialogs: They May Change The Current Directory

On some Windows operating systems (primarily Windows 95, 98, and ME), GetOpenFileName() and GetSaveFileName() (and wrappers of these functions such as MFC’s CFileDialog) will permanently change the process’s current working directory unless the OFN_NOCHANGEDIR option is specified. As you can imagine, this can easily break your application if you ever rely on the current working directory being set to a particular value (such as if you open files using relative paths).

Of course, it is best to eliminate any such current working directory assumptions from your application completely.

Be Careful With Bitfields

C++ c win32

Published: 2005-09-07

Consider the following piece of code (adapted from a real-world bug):

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BOOL IsDirectory(LPCTSTR strPathName)
{
    DWORD dwAtts = GetFileAttributes(strPathName);
    if (dwAtts == INVALID_FILE_ATTRIBUTES)
        return FALSE;
    return (dwAtts == FILE_ATTRIBUTE_DIRECTORY);
}

This function will work most of the time, but every now and again it will run across a directory which it will claim isn’t one. Why?