Is it possible to set type for define macro?

This is a discussion on Is it possible to set type for define macro? within the C++ Programming forums, part of the General Programming Boards category; If I define a macro: Code: //Can i do something *like* this? #define doSmth( <int>val ) {...elided...}...

  1. #1
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    Is it possible to set type for define macro?

    If I define a macro:

    Code:
    //Can i do something *like* this?
    #define doSmth( <int>val ) {...elided...}

  2. #2
    CSharpener vart's Avatar
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    macro is processed by preprocessor that has no idea about types. So what do you think will be answer to your question?
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  3. #3
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    Right, but isn't it really just adding code to your code and THEN compiling? Can't a compiler put in that code and then try compiling? (I guess not, just hopeful)

    I say this because when I define a macro that has in it a "dynamic_cast" call and then pass an object that has no virtual functions and is not of the proper type, the compiler alerts me and says that's an error. So I thought maybe it could do the checking during compile...

    Code:
    #define doSmth( obj ) 
    { \
         SomeClass* c;  \
         c = dynamic_cast<SomeClass*> obj; \
         ...elided... \
    }
    
    int main()
    {
         int i;
    
         //compiler knows enough to complain about the dynamic cast attempt on "i"
         doSmth( i );
    }
    Last edited by 6tr6tr; 04-16-2008 at 01:06 PM.

  4. #4
    i dont know Vicious's Avatar
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    I usually like to follow the personal rule of "If I can't help don't post", but sometimes my curiosity gets me.

    Why are you wanting to do something like this if I may ask?

    What would be the benefit over something like:

    Code:
    void doSmth(int val) {
        // rawr, inline me?
    }
    What is C++?

  5. #5
    CSharpener vart's Avatar
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    Right, but isn't it really just adding code to your code and THEN compiling?
    Compiling is done by compiler - it works with the output of the preprocessor. At this step no sign of macro is anywhere in a sight...

    preprocessor just replaces some character sequencies in your code with other character sequencies...
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    Basically, if you want to know about types, don't use macros. You can use inline functions or something instead. Then you can overload the functions to deal with different types. For example:
    Code:
    inline void print(int x) {
        std::cout << x << std::endl;
    }
    
    inline void print(const char *str) {
        std::cout << '"' << str << '"' << std::endl;
    }
    If you wanted more generic functions you could use templates as well. For example:
    Code:
    template <typename type>
    inline void print_address(type x) {
        std::cout << &x << std::endl;
    }
    
    template <typename type>
    inline void print_address(type *x) {
        std::cout << x << std::endl;
    }
    It all depends on what you're trying to do . . . .

    [edit] To expand on what the others said about macros:

    When you use code like
    Code:
    #define N 10
    int x = N;
    the preprocessor takes that and generates this:
    Code:
    int x = 10;
    The compiler only sees this modified version. It cannot know about #defines, which is why compiler errors from #defines can be weird. [/edit]
    dwk

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