struct IDXGIDevice1 *dxgiDevice (?dxgiDevice@@3PEAUIDXGIDevice1@@EA) already define in game.obj. this is my code: IDXGIDevice1* dxgiDevice = NULL; why?

This kind of error is often caused by defining a variable in a header file which is then included in multiple translation units (.cpp files).

one or more re definition in c++?

Accepted answer

RLWA32 45,691 Reputation points

2024-07-04T12:43:25.5133333+00:00

This kind of error is often caused by defining a variable in a header file which is then included in multiple translation units (.cpp files).
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mc 4,576 Reputation points

2024-07-05T07:50:00.36+00:00

how to write partial code in differenct cpp files? If I write some in .h file. I can only use it

in main.cpp? can not write the code in othere cpp files of the .h file?

in .h file:

void GetDevice();

void GetBitmap();

can i write the GetDevice in dev.cpp and GetBitmap in bit.cpp?

RLWA32 45,691 Reputation points

2024-07-05T08:28:15.1666667+00:00

can i write the GetDevice in dev.cpp and GetBitmap in bit.cpp?

Yes.

There's a difference between function declarations and variable definitions.

Try building an application with the following examples -

File Test.h

#pragma once void GetDevice(); void GetBitmap(); // Uncomment to causes multiple definition error //int non_const_variable; const int const_variable = 42; // const variable is OK extern int extern_variable; // declaration as extern is OK, definition in one .cpp file

File main.cpp

#include <stdio.h> #include "Test.h" int extern_variable = 100; int main() { GetBitmap(); GetDevice(); return 0; }

File dev.cpp

#include <stdio.h> #include "Test.h" void GetDevice() { printf("In GetDevice(), const variable is %d, extern variable is %d\n", const_variable, extern_variable); }

File bit.cpp

#include <stdio.h> #include "Test.h" void GetBitmap() { printf("In GetBitmap(), const variable is %d, extern variable is %d\n", const_variable, extern_variable); }

mc 4,576 Reputation points

2024-07-06T13:28:48.7+00:00

extern ID2D1Factory *factory=NULL in header.h but still error. already definition in game.obj.

RLWA32 45,691 Reputation points

2024-07-06T14:33:38.64+00:00

You did not follow the example that I posted. If you go back and look at the way the extern variable is declared in test.h you will notice that it is not initialized. Initialization takes place only once in the main.cpp file.
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one or more re definition in c++?

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