Question

I am trying to create bunch of void methods and call them later in program.
I will demonstrate the code ahead to help better understand my issue.

.h file
static float sfloat;
namespace someNamespace
{
static void foo();
}
.cpp file
void someNamespace::foo(){cout<<sfloat<<endl}

• above code is simpler version of class that I was working on.

I initialize sfloat in other .cpp file

otherFile.cpp
void initializeAndUseFoo(){sfloat = 5; someNamespace::foo();}

As far as my understanding goes, I expect foo to print out 5 but it prints out 0 instead.
This behavior occurs across all other static variables that I have as well(pointer included). It seemed that somehow the variables inside the function are never initialized as the value I assign.

However if I call out “sfloat” not through the function then I can call it out properly.(if I just print it out on console with just

cout<<"just print it not through the function : " <<sfloat<<endl;

then it is indeed 5

Thank you for reading.

Answer 1

A global static variable is static within one compilation unit. If you make another compilation unit, it will have a separate copy of that static variable.

This SO question explains what a compilation unit is in C++.

Since your variable is static and global in the same time, there will be a single instance of it in it’s compilation unit. If you want to access that exact variable from another file, you will have to use the extern keyword. Without it, a new copy of that variable will be created in each compilation unit. You can find some information here, for example.