Initializer List or Constructor Body: When Should You Use Which in C ?

Initializer List vs Constructor Body: Understanding the Differences

In C , initializing member variables within a constructor can be done using either an initializer list or within the constructor body. While they may initially appear to achieve the same result, there are some subtle differences to consider.

Initializer List:

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

An initializer list is a comma-separated list of member initializers that follows the constructor parameters list. Each initializer assigns a value to the corresponding member variable. This syntax ensures that member variables are initialized before the constructor body executes.

Constructor Body:

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

Within the constructor body, member variables are initialized using assignment statements. This syntax allows for more complex initialization logic after the constructor parameters have been set.

Key Differences:

• Initialization Order: With an initializer list, members are initialized before the constructor body executes, while in the constructor body, members are initialized after the body executes.
• Default Construction: If member variables are non-POD (Plain Old Data) types and do not have default constructors, the constructor body approach will fail to compile. The initializer list ensures that default constructors are called before the constructor body.

Default Parameters:

Both methods handle default parameters in the same way. If default parameters are specified in the constructor declaration, they will be used for any missing arguments passed to the constructor.

Conclusion:

While both approaches can initialize member variables within a constructor, the initializer list is generally preferred for non-POD types to ensure proper initialization order and avoid compilation errors. The constructor body is useful for more complex initialization logic that requires additional code after the constructor parameters have been set.

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