Member Initializer List vs. Assignment in C Constructors: When Should I Use Which?

Initialization List vs. Assignment in Constructor

In C , there are two common approaches to initializing class members in a constructor: using a member initializer list or assigning values directly within the constructor. While syntactically different, there can be subtle differences in code generation and usage scenarios.

Member Initializer List

A member initializer list is a comma-separated list of member initializations that is placed within the constructor after the colon (:). In the example you provided:

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

This initializes the three member variables _capacity, _data, and _len with the specified values. This syntax is preferred for initializing constant members, references, and base class constructors.

Assignment in Constructor

In the alternative approach, you can assign values to member variables within the constructor body:

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

This syntax is more common for initializing non-constant member variables.

Code Generation and Optimization

The compiler typically generates optimized code for both approaches. In most cases, the resulting assembly code is identical. However, in rare cases, using the member initializer list can result in more efficient code when initializing constant members or when setting default values.

Usage Scenarios

As mentioned above, the member initializer list is required for initializing constant members, references, and base class constructors. For other member variables, either approach is acceptable. However, it is considered best practice to use the member initializer list for initializing member variables that have non-trivial construction or initialization requirements.

In the specific case of your example, using the member initializer list or assigning values in the constructor makes no practical difference.

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