Static Variable

You should never put static variables in a header file because the header file may be included multiple times in the same program. You should define static and global objects in a .cpp file.

Agreed that you should put it in the cpp, but since its static, does the compiler only declare it once ? I.E. no multiple include problems if you DO put in the header? I would just try it and see but I dont trust modern compilers to bomb on incorrect code -- often, illegal stuff works just fine.

Agreed that you should put it in the cpp, but since its static, does the compiler only declare it once ? I.E. no multiple include problems if you DO put in the header? I would just try it and see but I dont trust modern compilers to bomb on incorrect code -- often, illegal stuff works just fine.
This is a fundamental concept of C/C++: you can declare the static variable multiple times. You must define it only once. That's why you must separate the definition from the declaration. If the definition occurs mutiple times in different sources, you *will* get multiple copies of the same static variable which could lead to linker errors if the linker is smart enough, or other bugs that are much worse. Think of functions: you can declare them many times, but you must define them only in one place. inline functions are trickier, they can be defined in several places (i.e., in every .cpp file that includes a .h file with a definition of the inline function) but in this case there are (usually) no multiple copies because the function, once inlined, is no longer a function.