Thread: Macros Vs Inline functions

  1. #1
    Registered User
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    Jan 2006

    Macros Vs Inline functions


    Could someone explain which of the two: Macros or Inline functions produces smaller sized object code and why?


    Passionate Guy

  2. #2
    Registered User major_small's Avatar
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    May 2003
    depends on your compiler.

    Macros are bad.
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  3. #3
    Registered User Micko's Avatar
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    Nov 2003
    Read this:
    Inline functions and macros...
    "they are different in some important ways. For example, since inline functions are part of the language, it is generally possible to step through them in a debugger, whereas macros are notoriously difficult to debug. Also, macro parameters that have side effects can cause surprises if the parameter appears more than once (or not at all) in the body of the macro, whereas inline functions don't have these problems. Finally, macros are always expanded, but inline functions aren't always inlined.
    I think of macros as a simple text replace during preprocessing phase of compilation.
    Look at this example of using macros:
    #include <iostream>
    using namespace std;
    #define square(x) x*x
    int main()
    	int x = 10;
    	int a = 3, b = 5;
    	cout<< square(x)<<endl;
    	cout<< square(a+b)<<endl;
    	return 0;
    Result is not what you expect is it?
    Solution to this problem is using:
    #define square(x) (x)*(x)
    And when you need to take care of such things every time, it is very easy to make mistake.


    - Micko
    Gotta love the "please fix this for me, but I'm not going to tell you which functions we're allowed to use" posts.
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  4. #4
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    Jan 2006
    Thanks Micko for the detailed example. I understand the vulnerabilities of using Macros.

    But as major_small has suggested even I guess that the size of object code will vary depending on the compiler.

  5. #5
    and the hat of int overfl Salem's Avatar
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    Aug 2001
    The edge of the known universe
    Inline has a tendency to make code bigger, not smaller.

    You're saving the cost of a function call by pasting the context of the function directly into the caller. If you call an inline function a lot, that's going to bloat the exe with lots of near-identical code.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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