make variables visible on multiple files

This is a discussion on make variables visible on multiple files within the C++ Programming forums, part of the General Programming Boards category; How can I make a variable visible on different C++ source files? In other words, can I declare a variable ...

  1. #1
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    make variables visible on multiple files

    How can I make a variable visible on different C++ source files? In other words, can I declare a variable with a scope that's wider than the "file" level? I understand it's a basic question but both my book and a friend of mine that used to be a professional c programmer weren't able to give me an answer, and I didn't find anything on the FAQ. I am writing something with QT 3 , and I need to pass some variables contained into a machine-generated ui source file (qtballit.ui.h) to another one (trajectory.ui.h) . 10x in advance!

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    Registered User hk_mp5kpdw's Avatar
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    Declare the variable in one file globally. In the other file declare the same variable globally as well but put the extern keyword specifier in front of everything:

    file1:
    Code:
    int myvar;
    file2:
    Code:
    extern int myvar;
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    Confused Magos's Avatar
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    In the cpp file declare it normally. In the header file (which you include in all other files that wants to access it) you declare it using extern (see above post).
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  4. #4
    Code Goddess Prelude's Avatar
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    >can I declare a variable with a scope that's wider than the "file" level?
    No, but you can include declarations in each file that you intend to use the variable and define it in a single location so that the linker continues to like you.

    >a friend of mine that used to be a professional c programmer weren't able to give me an answer
    That's odd. That's very odd. I would expect a professional to be familar with handling multiple file programs.
    My best code is written with the delete key.

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    C++ Developer XSquared's Avatar
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    Pfft. Who needs multiple files? It just takes me ten minutes to find the missing semicolon in my hundred-thousand lines of code.
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