A method of using global variables for C + + multiple files

Start the wrong approach

Declaring and defining variables in Global.h

int shareddata = 9;

Compilation error

Building Target:ctest
INVOKING:GCC C + + Linker
g++-  o "CTest"   
./src/ctest.o./SRC/GLOBAL.O /GLOBAL.O: (. data+0x0): ' Shareddata ' is defined several times
./SRC/CTEST.O: (. data+0x0): First time this definition
collect2: Error: LD return 1

The right approach,

In the Global.h header file declaration

extern int shareddata;

Class in the GLOBAL.CPP definition

int shareddata = 9;

And then call directly on the other file.

int main (void)
{
	cout<<shareddata<<endl;

return 0;
}

Without the header file, it is possible to declare it directly before the call.

extern int shareddata;

Look at the compilation

Make all 
building file:.. /src/ctest.cpp
INVOKING:GCC C + + Compiler g++-o0-g3-wall-c-fmessage-length=0-mmd-mp-mf "SRC/CTEST.D"
SR C/CTEST.D "-O" SRC/CTEST.O "". /src/ctest.cpp "
Finished building: ... /src/ctest.cpp
 
Building file:. /src/global.cpp
INVOKING:GCC C + + Compiler g++-o0-g3-wall-c-fmessage-length=0-mmd-mp-mf "SRC/GLOBAL.D"
SRC/GLOBAL.D "-O" SRC/GLOBAL.O "". /src/global.cpp "
Finished building: ... /src/global.cpp
 
Building Target:ctest
INVOKING:GCC C + + Linker
g++-  o "CTest"  . /SRC/GLOBAL.O   
finished building target:ctest

First step

CTest.cpp compiled to CTEST.O here the variables for the global file are actually used, since this phase only needs to include header files so that CTest.cpp know the declaration of the global file variable.

Part II

Global.cpp compiled to GLOBAL.O

Part III

Link CTEST.O and GLOBAL.O to generate executable ctest.