In my project I have multiple header and source files. Most of these files include a header file called settings.h
This file looks something like this
#ifndef EXTERNAL_H
#define EXTERNAL_H
#define processID 12
...
#endif // EXTERNAL_H
Now I noticed that if I change the processID from a define to a type such as this
int processID;
I start getting linker error. I wanted to know if there was a way for me to change the processID from a define to an int type.
The linker error is given by the fact that a symbol with the same name is generated in each source file that is including that header.
So solve that problem you have multiple choice but one in C++11 should be the way, which is the constexpr specifier:
constexpr int processID = 12;
Another solution would be to use static specifier but this will create a different variable with the same name in each source, only preventing clashes just because each symbol is hidden inside each source.
A third solution would be to use const int since a const value can't be modified then, regardless how many of them are generated in each source file, they would all resolve to the same value.
enum is meant to represent a set of finite possible values, which is not the case in this situation. Indeed I don't even use enum anymore since C++11 but enum class which avoids the problem.I wanted to know if there was a way for me to change the processID from a define to an int type.
The simplest way is to convert it to a const declaration:
const int processID = 12;
You would need to use extern int processID; in the header, BUT you would then need to write int processID = 12; in one of the source files - this is because the extern keyword specifies that the actual object exists somewhere else, it doesn't define it. If you did not declare the int in a source file you would instead get a linker error saying the object isn't defined.
Alternatively, const or constexpr will reduce the object to a local scope.
