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Thinking in C++
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The constructor initializer list

The special initialization point is called the constructor initializer list, and it was originally developed for use in inheritance (covered in Chapter 14). The constructor initializer list – which, as the name implies, occurs only in the definition of the constructor – is a list of “constructor calls” that occur after the function argument list and a colon, but before the opening brace of the constructor body. This is to remind you that the initialization in the list occurs before any of the main constructor code is executed. This is the place to put all const initializations. The proper form for const inside a class is shown here:

//: C08:ConstInitialization.cpp
// Initializing const in classes
#include <iostream>
using namespace std;

class Fred {
  const int size;
  Fred(int sz);
  void print();

Fred::Fred(int sz) : size(sz) {}
void Fred::print() { cout << size << endl; }

int main() {
  Fred a(1), b(2), c(3);
  a.print(), b.print(), c.print();
} ///:~

The form of the constructor initializer list shown above is confusing at first because you’re not used to seeing a built-in type treated as if it has a constructor.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire