Finding memory leaks in Win32

I’ve just discovered an interesting function to aid the Win32 programmer in finding eventual memory leaks in debugging mode, and with a very straightforward use: _CrtDumpMemoryLeaks.

The function compares the current memory state with the one at the program start, and if any unnalocated memory block is found, it returns TRUE and prints some debug information on the output window. So, to use it effectively, without false positives, one must call it when all objects are out of scope. Here’s an example:

#include <crtdbg.h>
#include <string>
int WINAPI wWinMain(HINSTANCE, HINSTANCE, LPWSTR, int)
{
	std::wstring name = L"abcdef";
	_CrtDumpMemoryLeaks(); // will accuse a leak!
	return 0;
}

In the code above, there will be a false positive, because the string object didn’t go out of scope yet, therefore its destructor wasn’t called so far, so there’s still memory allocated. But this would rather lead to our expectations:

#include <crtdbg.h>
#include <string>
int WINAPI wWinMain(HINSTANCE, HINSTANCE, LPWSTR, int)
{
	{
		std::wstring name = L"abcdef";
	}
	_CrtDumpMemoryLeaks(); // no leaks!
	return 0;
}

Now, since the string was declared within the scope of the nested block, its destructor will be called when the nested block ends, and no memory will remain allocated after it. This way, _CrtDumpMemoryLeaks will correctly report no leaks; indeed, nothing will be printed to the output window.

And the function is removed when _DEBUG is not defined, so you don’t need to worry about it on your release builds.

I particularly found it useful to use the _CrtDumpMemoryLeaks call inside an _ASSERT macro, so that when a memory leak is found, a huge popup will honk right in my face, in addition to the debug messages. So I actually proceed like this:

_ASSERT(!_CrtDumpMemoryLeaks());

Portable Git on Windows

I use Git on Linux a lot, but these days I was willing to use it on Windows too. I remember some time ago I found some ugly installers, so I thought there should be a portable package. For my surprise, I found one: msysgit. It’s a self-contained package build upon MinGW with everything one would need.

And it’s incredibly easy to use: just unzip the package anywhere, then doubleclick “git-bash.bat”. Like magic, you have a Linux-like terminal with a ready-to-use Git. And all the stuff exhales quality: it seems to be very well built and feels good on the tip of the fingers.

Now if you need to use Git on Windows, there’s no other way to go but msysgit.

Load Explorer file extension icon in Win32

When programming with C and Win32, sometimes you need to load an icon, as displayed on Windows Explorer, relative to a file extension. For example, you need to load the Explorer icon associated to the “txt” file extension.

Here is a quick function I use to do it:

HICON ExplorerIcon(const wchar_t *fileExtension)
{
	wchar_t extens[10];
	SHFILEINFO shfi = { 0 };

	lstrcpy(extens, L"*.");
	lstrcat(extens, fileExtension);
	SHGetFileInfo(extens, FILE_ATTRIBUTE_NORMAL, &shfi, sizeof(shfi),
		SHGFI_TYPENAME | SHGFI_USEFILEATTRIBUTES);
	SHGetFileInfo(extens, FILE_ATTRIBUTE_NORMAL, &shfi, sizeof(shfi),
		SHGFI_ICON | SHGFI_SMALLICON | SHGFI_SYSICONINDEX | SHGFI_USEFILEATTRIBUTES);

	return shfi.hIcon; // use DestroyIcon() on this handle
}

// Usage example:
HICON hIconTxt = ExplorerIcon(L"txt");

Remember to release the HICON handle by calling DestroyIcon after using it, or you’ll have a resource leak.

My Firefox addons

Just to mention, these are the addons I’m using today on my Firefox 10.0.2:

• Adblock Plus 2.0.3 — Blocks all advertising content according to filters. I use to install this addon wherever computer I am at, and apart from a few subscriptions, I also have a couple rules of my own.
• Download Statusbar 0.9.10 — Replaces the traditional download window with small progress bars at the bottom of Firefox.
• Element Hiding Helper for Adblock Plus 1.2.1 — Extra functionality to Adblock Plus, easing the process of select specific elements within a page for adding blocking rules.
• F6 0.2 — When working with the tabs on top, when you hit F6 key you put the focus on the tabs, instead of the address bar. This addon makes sure that the address bar will be focused when you hit F6.
• Flagfox 4.1.12 — Displays a flag from the country where the site is from, not by its country code top level domain, but rather by its server location, determined by its IP address.
• Forecastfox 2.0.21 — Adds a weather monitor on the toolbar, displaying current weather and temperature. I was told the data is picked up from airports. It has shown to be fairly accurate.
• UI Fixer 1.4.4 — Rearranges the horrible design of new Firefox interface, for example, restoring the text on the titlebar and placing the orange button at the toolbar.
• Undo Close Tab Replacement 6 — Shows a list of the most recently closed pages, so any of them can be reopened again.