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difference between void and static void function

This is a discussion on difference between void and static void function within the C++ Programming forums, part of the General Programming Boards category; What is the difference between Code: void func(); and Code: static void func(); I have a Codeblocks project with two ...

  1. #1
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    difference between void and static void function

    What is the difference between
    Code:
     void func();
    and
    Code:
    static void func();
    I have a Codeblocks project with two files, main.cpp and main2.cpp.

    main.cpp
    Code:
    #include <iostream>
    #include"main2.cpp"
    using namespace std;
    void fnc_in_main(){
        cout<<"This is fnc_in_main() in main.cpp"<<endl;
    }
    int main()
    {
        cout << "This is main() in main.cpp" << endl;
        fnc_in_main();
        fnc_in_main2();
        return 0;
    }
    main2.cpp
    Code:
    #include <iostream>
    using namespace std;
    static void fnc_in_main2(){
        cout<<"This is fnc_in_main2() in main2.cpp"<<endl;
    }
    in main.cpp, if I don't write
    Code:
    #include"main2.cpp"
    the compiler gives an error saying fnc_in_main2() is not defined

    in main2.cpp, if I do not write
    Code:
    static void fnc_in_main2(){
    the compiler says fnc_in_main2() has been declared multiple times and says the multiple declaration occurred in main2.cpp.

    However, it says here that declaring a function static makes it visible only in the file in which the function was declared, but in my program it looks like making it static actually caused it to be visible in the other file main.cpp.

    Could someone please give me any idea about static functions and working with multiple files? Also, I think static functions inside a class works differently right?
    Again, I did the compiling from codeblocks in this case. If I have to compile multiple files in gcc from the command line, how would I give the command?

    Thanks in advance

  2. #2
    C++ Witch laserlight's Avatar
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    The problem is that you attempted to use fnc_in_main2 in main before it was declared. The solution is to forward declare fnc_in_main2. Such a forward declaration might be placed in a header file.

    Your solution with static works because you then end up with two functions named fnc_in_main2: one is visible only in main.cpp and the other is visible only in main2.cpp. As such, you don't break the one definition rule, although the solution sucks because you really only needed one such function.
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  3. #3
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    so what's happening here is, when I use #include, a copy of main2.cpp is made in main.cpp?
    So for this to work I need to put the function in main2.cpp in some header file with header guards?

  4. #4
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by mahaju
    when I use #include, a copy of main2.cpp is made in main.cpp?
    Yes.

    Quote Originally Posted by mahaju
    So for this to work I need to put the function in main2.cpp in some header file with header guards?
    Yes, a declaration, but not the definition, of the function. The definition of the function can stay in main2.cpp
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    so what does it mean by working with multiple files in large projects, if all the function definitions go into the header files and we just need one cpp file with int main() ?

  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by mahaju
    so what does it mean by working with multiple files in large projects, if all the function definitions go into the header files and we just need one cpp file with int main() ?
    That means that you're probably doing it wrong
    stahta01 likes this.
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  7. #7
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    ok I think I understand it a bit
    Thank you very much for your help

  8. #8
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