CODEWITHSUNDEEP
c++c++11
Scholle
Scholle

Reputation: 1521

How to use a constructor parameter within the same constructor?

I want to use a constructor parameter some_function as parameter to a default initialization of some other constructor parameter, namely some_other_function:

SomeConstructor(SomeFunction some_function,
                SomeOtherFunction some_other_function = SomeOtherFunction(some_function)) :
      some_function_(some_function),
      some_other_function_(some_other_function) 
{...}

Unfortunately, this gives a compile error:

error: 'some_function' was not declared in this scope

Upvotes: 2

Views: 138

Answers (1)

Daniel Jour
Daniel Jour

Reputation: 16156

Just do it without the syntactic sugar(*):

Constructor (A a, B b)
  : a_(a), b_(b) {
  // ...
}
Constructor (A a)
  : Constructor (a, B(a)) {}

Though this only works since C++11, the feature is known as delegating or forwarding constructors.

(*) "syntactic sugar" isn't really the correct term here, as it's not semantically equivalent to the constructor with the default argument. (Default parameters are - as far as I know - inserted as "normal" parameters at the call site.)

Upvotes: 6

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