How Can I Check if a C Class Has a Member Function with a Specific Signature?

Checking Member Function Existence with Custom Signature

In this article, we address the challenge of determining whether a C class possesses a specific member function with a specified signature. Unlike the issue discussed in Scott Meyers' book, the goal here is to distinguish between classes possessing and lacking the function.

Template Trick

To achieve this, we introduce a template trick that leverages C 11 features. The has_serialize template structure serves as the primary template and asserts that the second template parameter must be a function type.

Specialization for Function Verification

A specialization of the has_serialize template handles the actual function verification. It employs two template functions:

• check: Attempts to call the specified method on a dummy object and checks the return type against the expected type.
• type: Determines whether the return type of the check function matches the expected type.

Function Verification

To test for the existence of a particular function f(Args...) with signature Ret(Args...) in class C:

std::cout << has_serialize<C, Ret(Args...)>::value << endl;

Example Usage

In the following example, we define two classes, X and Y, where Y inherits from X. Class X has a member function serialize(const std::string&) that returns an int.

Using the has_serialize template, we can verify that both X and Y possess the serialize function with the correct signature:

struct X {
     int serialize(const std::string&) { return 42; } 
};

struct Y : X {};

std::cout << has_serialize<X, int(const std::string&amp;)>::value << endl; // 1 (true)
std::cout << has_serialize<Y, int(const std::string&amp;)>::value << endl; // 1 (true)

This demonstrates how the has_serialize template trick can effectively detect whether a class contains a specific member function of a given signature.

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