Multiply defined structure error

I had a big main .cpp file with everything in it .I needed to break the code and so I created a helper.h where I moved all the typedefs, function declarations etc.Now I am tryin开发者_运维知识库g to move some of the functions from main .cpp into helper.cpp .I had a global called mypoint* originalpoint[mypoint is a stucture I defined in helper.h].I moved it into helper.h and placed one of the functions that uses it into helper.cpp .It is throwing this error now :-

Error   1   error LNK2005: "struct mypoint * originalpoints" (?originalpoints@@3PAUmypoint@@A) already defined in Main.obj  Helper.obj  Stereo002
Error   2   fatal error LNK1169: one or more multiply defined symbols found C:\Documents and Settings\Raj\My Documents\Visual Studio 2008\Projects\Stereo002\Debug\Stereo002.exe    1   Stereo002

I am not sure why is it saying multiply defined.I have everything in helper.h .I include helper.h into main.cpp and helper.cpp.

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You put the creation of a variable into the .h file, so it's being created in both .cpp files.

The way to fix this is to declare it as extern in the .h file, and duplicate it without the extern in one of the .cpps.

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In this case, since your header is included in two places, the compiler will create an instance of that variable for each time it is included. When the linker runs next, it finds two definitions for 'originalpoint' and complains.

Mark's answer is correct - in order to work around this issue, you can specify the variable as having external linkage by declaring it 'extern', which tells the linker to look for the declaration of this variable elsewhere (in one of the cpp files). Then, you actually declare it in one of the cpp files.

It is worth confirming that this is indeed what you want - one variable shared between the two files. Since they were originally part of the same implementation file, this is probably the desired effect.