Mastering Non-Standard Syntax: Using '&' to Create Pointers to Members in C++

In this guide, we'll discuss the non-standard C++ syntax for creating pointers to class members using the & operator. Although this syntax is non-standard and not recommended for new code, it's essential to understand it when working with legacy codebases or older libraries. By the end of this guide, you'll know how to create and use pointers to members with the & operator in C++.

Table of Contents

1. Introduction to Pointers to Members
2. Creating Pointers to Members using &
3. Using Pointers to Members
4. Advantages and Disadvantages of Using &
5. FAQs
6. Related Links

Introduction to Pointers to Members

Pointers to members are a feature in C++ that allows you to store the address of a class member, such as a data member or a member function. You can then use the stored address to access or call the member indirectly, similar to how regular pointers work with variables and functions.

Here's an example of a pointer to a member function:

class MyClass {
public:
    void myFunction() {
        // ... do something ...
    }
};

// Declare a pointer to the member function
void (MyClass::*pointerToMemberFunction)() = &MyClass::myFunction;

Notice that the syntax for declaring a pointer to a member function is different from regular pointers. You need to specify the class name, followed by the ::* operator and the pointer name, and then the function signature. You can then use the & operator to get the address of the member function.

Creating Pointers to Members using &

To create a pointer to a member using the & operator, you need to follow these steps:

1. Define the class and its members: First, you need to define a class with the data members and member functions you want to create pointers to.

class MyClass {
public:
    int myDataMember;
    void myMemberFunction() {
        // ... do something ...
    }
};

1. Declare the pointers to members: Next, declare the pointers to the data member and member function using the ::* operator.

int MyClass::*pointerToDataMember = &MyClass::myDataMember;
void (MyClass::*pointerToMemberFunction)() = &MyClass::myMemberFunction;

1. Initialize the pointers: Finally, initialize the pointers with the addresses of the corresponding members using the & operator.

pointerToDataMember = &MyClass::myDataMember;
pointerToMemberFunction = &MyClass::myMemberFunction;

Using Pointers to Members

To use pointers to members, you need to follow these steps:

1. Create an instance of the class: First, create an instance of the class that you want to access its members indirectly.

MyClass myObject;

1. Access the data member: To access the data member through the pointer, use the ->* operator with the object and the pointer.

myObject.*pointerToDataMember = 42; // Set the value of myDataMember to 42

1. Call the member function: To call the member function through the pointer, use the ->* operator with the object and the pointer.

(myObject.*pointerToMemberFunction)(); // Call myMemberFunction

Advantages and Disadvantages of Using &

Using the & operator to create pointers to members has its advantages and disadvantages:

Advantages

• Compatibility with legacy code: Understanding the & syntax is essential when working with older codebases or libraries that use this non-standard syntax.
• Indirection: Pointers to members allow you to access or call class members indirectly, which can be useful in some situations, such as implementing delegates or callbacks.

Disadvantages

• Non-standard syntax: The & syntax is non-standard and not recommended for new code. Instead, you should use the standard syntax for pointers to members with the ::* operator.
• Complexity: Pointers to members can make your code more complex and harder to understand, especially for developers not familiar with this feature.

FAQs

1. Should I use the & syntax for pointers to members in new code? {#faqs}

No, you should not use the & syntax for pointers to members in new code. This syntax is non-standard and not recommended. Instead, you should use the standard syntax for pointers to members with the ::* operator.

2. Can I use pointers to members with inheritance and polymorphism? {#faqs}

Yes, you can use pointers to members with inheritance and polymorphism. However, you need to be aware of some rules and restrictions, such as the pointers to base class members cannot be used directly with derived class objects.

3. Can I use pointers to members with static members? {#faqs}

No, you cannot use pointers to members with static members. Static members belong to the class itself, not to individual objects, so it doesn't make sense to create pointers to them.

4. Can I use pointers to members with overloaded functions? {#faqs}

Yes, you can use pointers to members with overloaded functions. However, you need to specify the correct function signature when declaring the pointer to avoid ambiguity.

5. Can I use pointers to members with templates? {#faqs}

Yes, you can use pointers to members with templates. However, you need to be aware of some rules and restrictions, such as the template arguments must be known at compile-time to create a pointer to a member.

Related Links

• Pointers to members in C++ (cplusplus.com)
• A Tour of C++: Pointers to Member Functions (bogotobogo.com)
• C++ Pointers to Class Members (programiz.com)