Thread: Avoiding Global variables

Originally Posted by csonx_p

I've learned at school that i should avoid Global declarations... But now with windows API i noticed all variables to be used or updated in WM_PAINT after every WM_COMMAND need to be global, otherwise won't update... Is there a limit here? and is my perception correct

They don't need to be global - they just need to be the same variable. Local variables in a function are "recreated" every time the function is called.

You have local variables that are static, which means that the variable remains each time.

There are also, usually, many other ways to have local but persistent storage - the typical way is to pass something from a "never ending" function to the lower level function, which is some sort of struct that contains your actual "global" variables.

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Mats

Like Abachler, I don't have a religious conviction that global variables are all bad. They are, to again echo Abachler, a tool. A hammer is a tool - if you use it incorrectly your thumb, or the walls in your house, may get damaged. But use it correctly with nails, and you can build a house. A knife can kill people, but it's also a useful tool to cut up your meat or vegetables to make your dinner.

So, used with care and for the right reasons, global variables are "OK". There are a few problems with global variables:
1. It's hard to know when and where they get changed.
2. There is a risk of name collisions when merging source from different places.
3. It is harder to change the behaviour of the code if global variables are used too much - for example if you want to create another of something, it's quite easy when it's being passed around as a parameter to various functions, but if it's one global variable, you need to create another variable and then go around and change all the code that uses the first variable to KNOW which one to use at what times.

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Mats

Originally Posted by csonx_p

Mats i declare a variable to contain a handle to an edit control inside the WinProc, initialized within WM_CREATE. But i intend to use this variable within WM_PAINT and would sometimes refresh (call InvalidateRect) WM_PAINT.. I noticed that i don't get it initialized properly unless i move its declaration globally. So you suggest i should declare it as static rather within WinProc? There are few others which would need same resolution

And you are using C?

Originally Posted by csonx_p

Yes, supposedly... Well my files are .cpp (whilst writing c code) cause i can't compile .c files successfully in Visual Studio 2005 standard Edition...

Why not - Visual Studio (all versions, including 2008) can compile C code. Presumably you are either using C++ features, or something else is wrong in your code... What error(s) do you get?

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Mats

Originally Posted by csonx_p

I just renamed the .cpp file to .c and hit compile, I get a pre-compile header error... turning them of gives billion errors

Yeah, you probably need to do a clean before you build (rebuild all or whatever it's called in MS speak), as the precompiled headers will "know" whether you are using C++ or C when compiling the header, so if you just rename the file, it will still think the precompiled header is the same [my personal opinion is that precompiled headers are only worth-wile in big projects - in small projects the saving is pretty small, really].

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Mats