Member Initializer List vs. Constructor Assignment: When Should You Use Which?

Initialization List vs. Constructor Assignments: Internal and Code Differences

In the given C code, there's a question regarding the differences between using a member initializer list and assigning values in a constructor.

Member Initializer List

The member initializer list, enclosed in parentheses after the constructor name, is used to initialize:

• Constant members
• References (not pointers)
• Base class members (parameters to the base class constructor)

Constructor Assignments

Constructor assignments, on the other hand, are used to initialize non-constant members and assign values to non-reference variables.

Internal Differences

Internally, the generated code is slightly different between the two approaches. When using a member initializer list, the compiler places the member values directly into the class object during construction. This avoids extra assignment operations.

Code Differences

Comparing the given code snippets:

MyClass::MyClass() : _capacity(15), _data(NULL), _len(0)
{
}

MyClass::MyClass()
{
  _capacity = 15;
  _data = NULL;
  _len = 0;
}

Both snippets will initialize the three private members _capacity, _data, and _len with the specified values. However, the first snippet uses a member initializer list, while the second snippet uses constructor assignments.

When to Use Member Initializer Lists

Initialization lists must be used:

• To initialize constant members
• To initialize references
• To pass arguments to base class constructors

For standard initialization (non-constant members, non-references), either approach can be used. In general, member initializer lists are preferred for efficiency reasons.

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