Why Don\'t C Compilers Automatically Generate Equality (==) and Inequality (!=) Operators?

Why C Compilers Don't Auto-Define Equality and Inequality Operators

In C , the compiler automatically provides default implementations for certain operations, including constructors, assignment operators, and destructors. However, it does not generate default equality (==) and inequality (!=) operators.

Reason for the Exclusion

The decision to not provide default equality operators stems from the potential issues associated with member-by-member comparisons. If a class handles memory allocation or contains complex data structures, a default comparison may lead to unexpected results or erroneous behavior.

Stroustrup's Perspective

The C creator, Bjarne Stroustrup, has expressed concerns about automatic default copy constructors. He believes that copying should be explicitly controlled by programmers, and he discourages its use for specific object types.

Consequences for Programmers

The absence of compiler-generated equality operators means programmers must write custom comparison functions for their classes. This additional responsibility ensures that complex classes are compared correctly without compromising data integrity.

Example

Consider the following class:

class Foo {
public:
    std::string str_;
    int n_;
};

To compare objects of this class, the programmer must implement the equality operator:

bool operator==(const Foo& f1, const Foo& f2) {
    return (f1.str_ == f2.str_ && f1.n_ == f2.n_);
}

Conclusion

C compilers do not auto-define equality and inequality operators to prevent potential errors and maintain control over object comparison. Programmers must define custom comparison functions for complex classes to ensure accurate and reliable comparisons of class instances.

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