C++ Attempting To Reference A Deleted Function

4 min read Jul 01, 2024

C++: Attempting to Reference a Deleted Function

In C++, deleted functions are functions that are explicitly prevented from being called. This is done by using the = delete specifier in the function declaration. The compiler will then generate an error if someone attempts to call the deleted function.

This feature is particularly useful for several reasons:

Why Use Deleted Functions?

Preventing Unwanted Usage: Deleted functions can be used to prevent accidental or unintended usage of certain functions. This helps to maintain code consistency and prevent potential errors.
Enforcing Design Constraints: Deleted functions can be used to enforce design constraints. For example, a class might have a copy constructor and assignment operator deleted to prevent objects of that class from being copied or assigned. This can be crucial for classes that manage unique resources or have specific ownership semantics.
Improving Code Clarity: Deleted functions clearly indicate which functions are not meant to be called, improving the readability and understandability of your code.

Common Scenarios

Here are some common scenarios where you might use deleted functions:

Preventing Copying and Assignment: To prevent objects of a class from being copied or assigned, you can delete the copy constructor and assignment operator:

class MyClass {
public:
    MyClass() = default; 
    MyClass(const MyClass&) = delete;
    MyClass& operator=(const MyClass&) = delete; 
    // ...
};

Preventing Conversion: You can delete conversion operators to prevent implicit conversions from one type to another:

class MyClass {
public:
    MyClass() = default;
    explicit MyClass(int value) {} // Explicit constructor
    operator int() = delete;   // Prevent implicit conversion to int
};

Preventing Function Calls in Specific Contexts: You can delete specific function overloads to restrict their usage in certain contexts:

class MyClass {
public:
    void doSomething(int value) {}
    void doSomething(const std::string& str) = delete; // Deleted overload for string
};

Example: Deleted Copy Constructor

#include 

class MyClass {
public:
    MyClass() : value(0) {}
    MyClass(int value) : value(value) {}

    // Deleted copy constructor
    MyClass(const MyClass&) = delete; 

    // Deleted assignment operator
    MyClass& operator=(const MyClass&) = delete;

    int getValue() const { return value; }

private:
    int value;
};

int main() {
    MyClass obj1(10);
    
    // This will result in a compilation error:
    // MyClass obj2 = obj1;  // Attempting to copy

    std::cout << "obj1's value: " << obj1.getValue() << std::endl; 
    
    return 0;
}

In this example, the copy constructor and assignment operator are deleted. This means that you cannot copy or assign MyClass objects. Attempting to do so will result in a compilation error, preventing potential issues related to unwanted copying.

Conclusion

Deleted functions are a powerful tool in C++ for controlling the usage of functions and enforcing design constraints. They provide a clear and unambiguous way to prevent unwanted function calls and improve the overall quality and robustness of your code.

C++ Attempting To Reference A Deleted Function