Initializer List or Constructor Body: Which is Best for C Field Initialization?

Initializer List vs. Constructor Body: Delving into Field Initialization

In the world of object-oriented programming with C , one common task is initializing class fields. While the initializer list and constructor body offer two distinct ways to do this, understanding the subtle difference between them is essential.

Initializer List

The initializer list syntax allows you to initialize member variables right at the beginning of the constructor, before its body executes. This is achieved using the : symbol, followed by a comma-separated list of assignments:

public: Thing(int _foo, int _bar): member1(_foo), member2(_bar) {}

Constructor Body

In the constructor body, field initialization occurs within the braces (after the parameter list). Each field is assigned explicitly using the equals sign:

public: Thing(int _foo, int _bar) {
    member1 = _foo;
    member2 = _bar;
}

Difference for Non-POD Types

When dealing with non-POD (Plain Old Data) types, there's a crucial distinction between these two methods. Unlike the initializer list, which initializes such fields immediately, the constructor body initializes them only after the execution of its body starts.

This means that the constructor body implicitly calls the default constructor for each non-POD member, potentially resulting in double initialization. For instance:

public: Thing(int _foo, int _bar) {
    member1 = _foo;
    member2 = _bar;
}

This is effectively equivalent to:

public: Thing(int _foo, int _bar) : member1(), member2() {
    member1 = _foo;
    member2 = _bar;
}

Safety Implications

This difference can have implications for safety. If a non-POD member lacks a default constructor, using the constructor body will cause a compilation error. In contrast, the initializer list will simply skip initializing the member, which may be desirable or unwanted depending on the situation.

Default Parameters

Both the initializer list and constructor body support default parameter values. However, the behavior is identical, and the choice of method does not influence how default parameters are handled.

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