Question

I have a set of global variables and a method in a cpp file.

int a;

int b;

int c;

void DoStuff()
{

}

in the header file I have declared them explicitly with the extern keyword. My problem is when I include the header file in another C++ file, I can’t use the external variables and the method. It’s giving a linker error saying error LNK2001: unresolved external symbol for the methods and variables. What have I done wrong here??

PS: DoStuff() method populates the variables. All the header files and cpp files are in the same project folder.

Thank You!

Answer 1

Try this

Define those variables inside your header instead of just declaring them.

extern int x; is just a declaration(not a definition)

Simple example

a.cpp

 int a,b,c; //definition

 void doStuff(){ 

 }

b.cpp

extern int a,b,c; //extern keyword is mandatory
void doStuff();   //extern keyword is optional because functions by default have external linkage

int main()
{

   doStuff();
}