what does ":" do in c++ code?

i'm trying to read and understand a .cc (c++)file,
i want to know what does ok_flag(false),time_range(false),prefix() do after ":" ?
I did know that ":" was being used for class inheritance but what is ":" for in the bleow code?

Code:

ClassA::ClassA(const char *db) : ok_flag(false),time_range(false),prefix()
{
//.. Constructor statements
}

plz help
thanx.

 

It initializes those variables in the class. It's more effective than putting statements inside the constructor.

 

ok,thanks.