Program structure (#include)

This is a discussion on Program structure (#include) within the C++ Programming forums, part of the General Programming Boards category; Hello. I was having a problem with a project of mine. I am new to makefiles and I haven't used ...

  1. #1
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    Program structure (#include)

    Hello.

    I was having a problem with a project of mine. I am new to makefiles and I haven't used complicated #include systems, but there appeared a problem with a system of mine:

    main.cpp def.h net_funcs.cpp are the files

    main.cpp includes def.h
    net_funcs.cpp includes def.h

    def.h contains some definitions
    (main.cpp and net_funcs.cpp both need some of the definitions in the def.h file)

    now I have this makefile:

    main.exe : main.o net_funcs.o
    g++ main.o net_funcs.o -Lc:/cpp/include -lws2_32
    main.o : main.cpp
    g++ main.cpp -c
    net_funcs.o : net_funcs.cpp
    g++ net_funcs.cpp -c

    when I run make, this will be done:

    main.cpp will be compiled (main.o will contain the definitions from def.h)
    net_funcs.cpp will be compiled(net_funcs.o will contain the definitions from def.h)
    Thus, both files contain the definitions.
    when the compiler tries to link them together ( g++ main.o net_funcs.o -Lc:/cpp/include -lws2_32 ) - a clash will occur(double definitions).

    So, do you have any ideas of how I should structure my program to make a nice #include system. Is there an universal good style to avoid clashes?

  2. #2
    CSharpener vart's Avatar
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    put definitions in the c file
    put extern declarations in h-file

    (even better - try to avoid global variables)
    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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    is there another way? I wouldn't like to use the extern keyword, but if there's not a better way, I'll use it. Thanks anyway.

    I need to use global variables like:
    const string servername = "www.google.com";

    defining them separately in every function that uses the servername, is bothersome

  4. #4
    CSharpener vart's Avatar
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    no there is not (except as I said - not using globals)
    if you still want global variable
    you put
    int i = 0; in c-file (there will be 1 instance of this variable)

    you put
    extern int i;
    in h-hile
    so every c-file including this h-file knows that somewhere else a global int i variable is defined
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  5. #5
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    what about function declarations?

    the extern thingy seemed to work for variables.

  6. #6
    CSharpener vart's Avatar
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    in h- file goes

    int Myfunc(int,char*,double);

    in c-file goes
    Code:
    int Myfunc(int len,char* buffer,double val)
    {
       return _snprintf(buffer,len,"%f",val);
    }
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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