When Does Using Initialization Lists Offer a Significant Performance Advantage in C ?

Benefits of Initialization Lists and Their Efficiency

Initialization lists are known for their efficiency in initializing class members that are not built-in types. This technique offers several advantages over traditional initialization methods.

In the example provided, Fred::Fred(): x_(whatever) {}, the compiler constructs the result of the expression directly inside the member variable x_, avoiding unnecessary copying and object construction. This eliminates the performance penalty associated with temporary object creation and destruction in the alternative approach, Fred::Fred() { x_ = whatever; }.

However, in the specific case you mentioned, with the following class:

class MyClass
{
public:
    MyClass(string n):name(n) { }
private:
    string name;
};

compared to the alternative:

class MyClass
{
public:
    MyClass(string n)
    {
        name=n;
    }
private:
    string name;
};

there is no significant efficiency gain in using an initialization list. In this case, the second version calls the default constructor of the string class and then its copy-assignment operator, which could potentially result in minor efficiency losses compared to the first version.

The recommendation is to consistently use the recommended initialization list approach to ensure code correctness and maintain readability, even in cases where there may not be a tangible performance benefit.

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