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This article mainly explains "Why should be careful of the equality operator of the base class in C++". The explanation in the article is simple and clear and easy to learn and understand. Please follow the editor's train of thought. Let's study and learn why we should be careful of the equality operator of the base class in C++.

Reason (reason)

It's really hard to write simple and easy-to-use equality operators for inheritance systems.

Example, bad (negative example) class B {

String name

Int number

Virtual bool operator== (const Ba) const

{

Return name = = a.name & & number = = a.number

}

/ /...

}

The second Operand of the equality comparison operator of B accepts type conversions, but the first one does not.

Class D: B {

Char character

Virtual bool operator== (const Da) const

{

Return name = = a.name & & number = = a.number & & character = = a.character

}

/ /...

}

B b =.

D d =.

B = = d; / / compares name and number, ignores d's character

D = = b; / / error: no = = defined

D d2

D = = D2; / / compares name, number, and character

B & b2 = D2

B2 = = d; / / compares name and number, ignores d2s and d's character

Of course, there is a way to make the equality comparison operator act in the inheritance system, but the simple method is not.

Note (Note)

This rule applies to all common comparison operators:! =, =.

Enforcement (implementation recommendations)

The hint is defined as the equality comparison operator of the virtual function; the same is true of other comparison operators:! =, =.

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