C + + methods for using global variables multiple files

The practice of starting the error

Declaring and defining variables in Global.h

int shareddata = 9;

Compilation error

Building Target:CTestInvoking:GCC C + + linkerg++-  o "CTest"  ./src/ctest.o./src/global.o./SRC/GLOBAL.O   :(. data+0x0): ' Shareddata ' is defined more than once./SRC/CTEST.O: (. data+0x0): First time in this definition collect2: Error: LD returns 1

The right approach.

In the Global.h header file declaration

extern int shareddata;

Initialization in Global.cpp definition

int shareddata = 9;

And then call it directly in the other files to be able to

int main (void) {Cout<<shareddata<<endl;return 0;}

Do not include the header file, directly before the call can be declared.

extern int shareddata;

Look at the compilation

Make all Building file:.  /SRC/CTEST.CPPINVOKING:GCC C + + compilerg++-o0-g3-wall-c-fmessage-length=0-mmd-mp-mf "src/CTest.d"-MT "SRC/CTEST.D" -O "SRC/CTEST.O" ". /src/ctest.cpp "Finished building: /src/ctest.cpp Building file:.. /SRC/GLOBAL.CPPINVOKING:GCC C + + compilerg++-o0-g3-wall-c-fmessage-length=0-mmd-mp-mf "SRC/GLOBAL.D"-MT "Src/global . D "-O" SRC/GLOBAL.O "". /src/global.cpp "Finished building: /src/global.cpp Building Target:CTestInvoking:GCC C + + linkerg++  -o "CTest"  ./src/ctest.o.   /SRC/GLOBAL.O Finished building Target:ctest

The first step

CTest.cpp compiled to CTEST.O here it is useful to the variables of the global file, because this stage only needs to include the header file, let CTest.cpp know the global file variable declaration can be.

Part II

Global.cpp compiled to GLOBAL.O

Part III

Links to CTEST.O and GLOBAL.O, generating a ctest that can run the file.

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C + + methods for using global variables multiple files