What is the Role of the Colon in a C Constructor?

Understanding the Role of the Colon in a C Constructor

In C , a constructor's implementation may include a member initializer list, which utilizes the colon (":") operator. This list serves to initialize object members with specific values without requiring explicit assignments in the constructor body.

Consider the following constructor:

class MyClass {
public:
    MyClass() : m_classID(-1), m_userdata(0) { }
    int m_classID;
    void *m_userdata;
};

The member initializer list ": m_classID(-1), m_userdata(0)" performs the following initialization:

• m_classID is set to -1.
• m_userdata is set to 0.

It's important to note that this initialization occurs before the constructor body is executed. As a result, assignments made within the body of the constructor are not initializations but rather value changes.

The member initializer list allows for direct initialization of object members, providing a concise alternative to explicit assignments. It is particularly useful when default values or specific values need to be assigned to member variables during object construction.

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