Thread: Uses of malloc()?

  1. #1
    Registered User
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    Sep 2011

    Uses of malloc()?

    I have seen this function quite a bit and I also see it is important in CUDA programming, so I decided that learning it earlier rather than later is best.

    From what I read it allocates memory but without a type, why would you want to do that? Why not just use int or char normally?

    My Ctrl+S addiction gets in the way when using Code Blocks...

  2. #2
    ATH0 quzah's Avatar
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    Oct 2001
    What if you want a char or an int but you don't know how many? Then you want to pass all of those around from one function to another to do things with them. Dynamically allocate a bunch of them, pass a pointer around to them.

    Hope is the first step on the road to disappointment.

  3. #3
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    May 2009
    Learn pointers before trying to learn malloc.

    Tim S.
    "...a computer is a stupid machine with the ability to do incredibly smart things, while computer programmers are smart people with the ability to do incredibly stupid things. They are,in short, a perfect match.." Bill Bryson

  4. #4
    Registered User ledow's Avatar
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    Dec 2011
    Malloc GIVES you a slab of memory. You can do what you like with it and it can be (virtually) as large as you like. It can even change size and type as and when you like. You also can have it so your program only takes up memory when it needs (i.e. a program that has to process 60Gb of data doesn't need 60Gb of statically-allocated char's all over the place!

    In contrast, allocating an int directly in the program will only ever give you an int's worth of memory and it's allocated from something called "the stack", which is far from able to hold all your data.

    Example: You write a game. You need to read in an image file. That image file can be tiny or huge, but you need to put it into memory in order to send it to the screen. You can't know until you run the program how large that image will be or how many bytes it will use (because the user is the one telling you what file to open). Thus you find out the filesize, malloc that amount of space, and read the file into memory. When you're done, you can "free" the memory and other programs can use it again.

    But, to be honest, if you don't understand that far, I wonder what you've ever done in terms of C programming (or even CUDA) at all.

    - Compiler warnings are like "Bridge Out Ahead" warnings. DON'T just ignore them.
    - A compiler error is something SO stupid that the compiler genuinely can't carry on with its job. A compiler warning is the compiler saying "Well, that's bloody stupid but if you WANT to ignore me..." and carrying on.
    - The best debugging tool in the world is a bunch of printf()'s for everything important around the bits you think might be wrong.

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