Question

I’ve got a couple of constructors for my class:

MyClass();
MyClass( int param1 );
MyClass( int param1, int param2 );
MyClass( std::string otherParam );
MyClass( std::string otherParam, int param1 );
MyClass( std::string otherParam, int param1, int param2 );

Now, there is some argument checking to be done in the constructor, e.g. -3 < param1 < 3. What’s the preferred way of doing this check? Should I call checkParam1() and checkOtherParam() from each constructor?

Answer 1

In C++11 you can use a delegated constructor feature:

With the delegating constructors feature, you can concentrate common initializations and post initializations in one constructor named target constructor. Delegating constructors can call the target constructor to do the initialization. A delegating constructor can also be used as the target constructor of one or more delegating constructors. You can use this feature to make programs more readable and maintainable.

MyClass( std::string otherParam, int param1, int param2 );

MyClass( std::string otherParam, int param1)
:   MyClass(otherParam, param1, 456) {
}

The constructor with fewer parameters calls the constructor with more parameters, and the constructor with the most parameters does all the checking.

Note that you should be able to unify the last three constructors by adding default values for param1 and param2, like this:

MyClass( std::string otherParam, int param1 = 123, int param2 = 456);