Where should you put global constants in a C++ program?

Question

Where would you put global constants in a C++ application? For example would you put them in a class? In a struct?

Answer 1

For constants local to a single .cpp file, the best approach is to declare them in an anonymous namespace like so:

namespace {
   int const seconds_per_minute = 60;
   int const minutes_per_hour   = 60;
}

For constants that need to be visible to the entire program, the simplest solution is to create a (named) namspace for them, and put that in a header file.

If there is (or might be) some operations to go with them, instead you should probably create a singleton class for them. For example, it is quite common that my programs have a singleton class named "configuration" that reads startup constants (stuff like IP addresses, and things I don't quite want to hard-code) from a config file or the registry or something like that.