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Base class assignment operator not called

Copy assignment operator does not call copy assignment operators of base subobjects

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Description

This defect occurs when a derived class copy assignment operator does not call the copy assignment operator of its base class.

Risk

If this defect occurs, unless you are initializing the base class data members explicitly in the derived class assignment operator, the operator initializes the members implicitly by using the default constructor of the base class. Therefore, it is possible that the base class data members do not get assigned the right values.

If users of your class expect your assignment operator to perform a complete assignment between two objects, they can face unintended consequences.

Fix

Call the base class copy assignment operator from the derived class copy assignment operator.

Even if the base class data members are not private, and you explicitly initialize the base class data members in the derived class copy assignment operator, replace this explicit initialization with a call to the base class copy assignment operator. Otherwise, determine why you retain the explicit initialization.

Examples

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class Base0 {
public:
    Base0();
    virtual ~Base0();
    Base0& operator=(const Base0&);
private:
    int _i;
};

class Base1 {
public:
    Base1();
    virtual ~Base1();
    Base1& operator=(const Base1&);
private:
    int _i;
};

class Derived: public Base0, Base1 {
public:
    Derived();
    ~Derived();
    Derived& operator=(const Derived& d) {
        if (&d == this) return *this;
        Base0::operator=(d);
        _j = d._j;
        return *this;
    }
private:
    int _j;
};

In this example, the class Derived is derived from two classes Base0 and Base1. In the copy assignment operator of Derived, only the copy assignment operator of Base0 is called. The copy assignment operator of Base1 is not called.

The defect appears on the copy assignment operator of the derived class. Following are some tips for navigating in the source code:

  • To find the derived class definition, right-click the derived class name and select Go To Definition.

  • To find the base class definition, first navigate to the derived class definition. In the derived class definition, right-click the base class name and select Go To Definition.

  • To find the definition of the base class copy assignment operator, first navigate to the base class definition. In the base class definition, right-click the operator name and select Go To Definition.

Correction — Call Base Class Copy Assignment Operator

If you want your copy assignment operator to perform a complete assignment, one possible correction is to call the copy assignment operator of class Base1.

class Base0 {
public:
    Base0();
    virtual ~Base0();
    Base0& operator=(const Base0&);
private:
    int _i;
};

class Base1 {
public:
    Base1();
    virtual ~Base1();
    Base1& operator=(const Base1&);
private:
    int _i;
};

class Derived: public Base0, Base1 {
public:
    Derived();
    ~Derived();
    Derived& operator=(const Derived& d) {
        if (&d == this) return *this;
        Base0::operator=(d);
        Base1::operator=(d);
        _j = d._j;
        return *this;
    }
private:
    int _j;
};

Result Information

Group: Object oriented
Language: C++
Default: On for handwritten code, off for generated code
Command-Line Syntax: MISSING_BASE_ASSIGN_OP_CALL
Impact: High

Version History

Introduced in R2015b

See Also

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