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

Initialization List vs Constructor Assignments: Internal Differences

When initializing class members, one can choose to use either a member initializer list or assign values within the constructor body. Internally, these approaches have subtle differences.

Member Initializer List

Using a member initializer list, as seen in this example:

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

initializes member variables directly before entering the constructor body. This is particularly useful for:

• Initializing constant members: These members must be initialized before the constructor body is executed, and a member initializer list is the only way to do so.
• Initializing references: References must be initialized before the constructor body, and a member initializer list is the preferred method.
• Passing parameters to base class constructors: When inheriting from a base class with a parameterized constructor, the base class members must be initialized using a member initializer list.

Constructor Assignments

On the other hand, assigning values within the constructor body, as in this example:

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

performs the initialization during the constructor execution. This approach is commonly used for non-constant members and members that can be initialized based on the constructor's parameters.

Comparison of Generated Code

Generally, both approaches generate similar code. However, in the case of constant members or references, only a member initializer list can initialize them, as constructor assignments would result in compilation errors.

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