What does '= delete' mean in C function declarations?

Understanding the Meaning of "= delete" in Function Declarations

In C 11, the "= delete" syntax is used to delete a function, effectively preventing its use. It is commonly employed to prohibit copying or to restrict certain conversions.

Deleting Copy Constructors and Assignment Operators

Perhaps the most common use case for "= delete" is to disallow copying. For instance, if we have a class called "my_class" that we do not want to be copied, we can declare:

class my_class
{
public:
    ...
    my_class(const my_class &) = delete;
    ...
};

This declaration prevents the compiler from generating a default copy constructor and assignment operator for "my_class."

Preventing Undesirable Conversions

Another use of "= delete" is to prohibit specific type conversions. For example, if we have a class "Z" that we want to be constructed only from "long long" values, we can use "= delete" to prevent conversions from smaller types:

struct Z
{
public:
    ...

    Z(long long);     // can initialize with a long long      
    Z(long) = delete; // but not anything less
};

Additional Function Modifiers

Besides "= 0" (which sets the function to pure virtual) and "= delete" (which deletes the function), there are no other function modifiers in C . However, other keywords such as "override" and "final" can be used to modify the behavior of virtual functions.

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