How important is managing memory in Objective-C?

Question

Background: I'm (jumping on the bandwagon and) starting learning about iPhone/iPad development and Objective-C. I have a great background in web development and most of my programming is done in javascript (no libraries), Ruby, and PHP.

Question: I'm learning about allocating and releasing memory in Objective-C, and I see it as quite a tricky task to layer on top of actually getting the farking thing to run. I'm trying to get a sense of applications that are out there and what will happen with a poorly memory-managed program.

A) Are apps usually released with no memory leaks? Is this a feasible goal, or do people more realistically just excise the worst offenders and that's ok?

B) If I make a NSString for a title of a view, let's say, and forget to deallocate it it, does this really only become a problem if I recreate that string repeatedly? I imagine what I'm doing is creating an overhead of the memory needed to store that string, so it's probably quite piddling (a few bytes?) However if I have a rapidly looping cycle in a game that 'leaks' an int every cycle or something, that would overflow the app quite quickly. Are these assumptions correct?

Sorry if this isn't up the community-wiki alley, I'm just trying to get a handle on how to think about memory and how careful I'll need to be. Any anecdotes or App Store-submitted app experiences would be awesome to hear as well.

Answer 1

I've taught courses on Cocoa development, and memory management is the second thing I teach (the first being C pointers). My experience has been that if a Cocoa programmer doesn't understand memory management, then he never amounts to much of a Cocoa programmer.

In other words, learn memory management. You won't regret it.

Answer 2

It is very important. Apple offers a tool for memory leak detection called Instruments.

This topic has previously bean discussed here as well: Memory leak detection tools in XCode

Answer 3

Your should never leak memory.

Consider: You today write some code that leaks memory only once during the execution of a program. Tomorrow, you reuse that code in some other way and it is executed many times. The leak is then problematic. Finding that leak may be very difficult. Much more difficult than making sure to always free your memory the first time you wrote the code.

Save yourself and others a headache down the road: always free your memory.

Answer 4

More important than life itself :p

Seriously though, just follow the rules in the links below and you'll be ok.

It becomes second nature after a while.

http://theuntitledblog.com/2010/05/25/objective-c-memory-management-rules/ http://developer.apple.com/iphone/library/documentation/cocoa/Conceptual/MemoryMgmt/Articles/mmObjectOwnership.html

Answer 5

Follow the patterns, and memory management is rarely the biggest roadblock in Cocoa.

However, I'm going to be a contrarian here: your sense is mostly correct. Leaking one NSString used as a label somewhere is not going to hurt anybody. Most apps of any complexity have multiple singletons around in the world holding state for the entire life of the app, and that's OK too (well, better, because it's explicit). So no, accidentally leaking a string once isn't going to kill you. Leaking big things (images, textures, file content data) will hurt you, though-- Apple doesn't guarantee any minimum or deterministic amount of memory for your process on the iPhone OS platform, so one or two of those leaks might result in users seeing frequent "crashes" in the field that you don't always see during development.

Be vigilant, use the patterns, and use the tools, and you'll be OK.