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I've just started experimenting with SDL in C++, and I thought checking for memory leaks regularly may be a good habit to form early on.
With this in mind, I've been running my 'Hello world' programs through Valgrind to catch any leaks, and although I've removed everything except the most basic SDL_Init() and SDL_Quit() statements, Valgrind still reports 120 bytes lost and 77k still reachable.
My question is: Is there an acceptable limit for memory leaks, or should I strive to make all my code completely leak-free?
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Memory is "leaking" out of the heap, never to be seen again. You allocate the memory, work with it until the program terminates. This is not a memory leak; it doesn't impair the program, and all the memory will be scavenged up automagically when the program terminates. Generally, you should avoid memory leaks.
Memory leaks are when programs on the computer incorrectly manage memory allocations. This is not uncommon on modern software and can cause performance drags on the system. The easiest way to fix this issue is to close and reopen the program with the leak, as it will reset the allocations.
Memory leaks don't result in physical or permanent damage. Since it's a software issue, it will slow down the applications or even your whole system. However, a program taking up a lot of RAM space doesn't always mean its memory is leaking somewhere. The program you're using may really need that much space.
Note: Applications with memory leaks can cause the CPU to work excessively. As a system's available RAM decreases, the system relies increasingly on the pagefile. The more heavily the pagefile is used, the more time is spent swapping pages between physical and virtual memory.
Be careful that Valgrind isn't picking up false positives in its measurements.
Many naive implementations of memory analyzers flag lost memory as a leak when it isn't really.
Maybe have a read of some of the papers in the external links section of the Wikipedia article on Purify. I know that the documentation that comes with Purify describes several scenarios where you get false positives when trying to detect memory leaks and then goes on to describe the techniques Purify uses to get around the issues.
BTW I'm not affiliated with IBM in any way. I've just used Purify extensively and will vouch for its effectiveness.
Edit: Here's an excellent introductory article covering memory monitoring. It's Purify specific but the discussion on types of memory errors is very interesting.
HTH.
cheers,
Rob
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