How to Pass Objects to Functions in C++ (With Examples)

Passing objects to functions in C++ is a basic concept that affects the performance, memory management, and object behaviour of the program. There are various methods by which objects can be passed to a function efficiently, and each method has its advantages. In this article, we will discuss passing an object to a function, passing an object as an argument, and different methods to pass an object to a function in C++.

Table of Contents:

• What Does It Mean to Pass Objects to Functions in C++?
• How to Pass Objects as Function Arguments in C++?
• Methods to Pass Objects to Functions in C++
  • Method 1: Passing by Value
  • Method 2: Passing by Reference
  • Method 3: Passing by Pointer
  • Method 4: Passing by Constant Reference
  • Method 5: Passing by Move (Using rvalue references)
• Pass by Value vs Reference vs Pointer vs Move
• Conclusion

What Does It Mean to Pass Object to Function in C++?

To pass object to function in C++ is the practice of providing an object of a class as an argument when calling a function, which allows the function to access and manipulate the data defined by that object. The way by which an object is passed to a function can affect performance, memory usage, and the ability to change the original object. 

How to Pass Objects as Function Arguments in C++?

To pass an object as an argument in C++, you must change the object name to the argument when calling the function, which allows the function to access the properties and methods of the object.

Syntax:

function_name(object_name);

Example:

Output:

The code shows how the Car object myCar is passed as an argument to the printCarDetails function by constant reference to access the data of the object without making a copy, which improves efficiency and keeps the original object unchanged.

Methods to Pass Objects to Functions in C++

Below are the five methods to pass object to function in C++.

Method 1: Passing by Value

When you are passing objects by value in a C++ program, a copy of that object is created and passed to the function, which allows changes to be made to that object inside the function, and the changes do not affect the original object outside the function. C++ Pass by value is useful in a few conditions, but can also lead to performance issues while dealing with large objects.

Example:

Output:

The code shows how the Circle object is pass by value to the changeRadius function by creating a separate copy of the object, and any changes inside the function can be applied to the copy only and not the original object as a result, the original Circle remains unchanged after the function call.

Method 2: Passing by Reference

When you are passing objects by reference in C++, it allows a function to operate on the original object instead of operating on a copy of the object. This method provides you with the ability to access the object directly by making changes that can affect the original object. It is often preferred for efficiency while dealing with large objects, as it avoids the overhead of copying.

Example:

Output:

The code shows how the Rectangle object is passed by reference to the scaleRectangle function, which allows direct changes in the original object, and the changes made inside the function affect the same object in the main() function.

Method 3: Passing by Pointer

Passing an object to the functions by pointer in C++ helps functions to get the memory address of an object through direct access and make changes in the original object. The pass by pointer is a useful method for handling dynamic memory allocation, and when you have to represent that a function might not operate on a valid object.

Example:

Output:

The code shows how the Student object is passed by a pointer to the updateStudentAge function, which allows direct changes in the original object. Also, the function checks for a null pointer at first before updating the student’s age.

Method 4: Passing by Constant Reference

When you pass an object to a function by constant reference in C++, it allows a function to get a reference to an object without making a copy and changes the object in the function. The C++ pass by reference method helps to combine the efficiency of C++ pass by reference with the safety of avoiding changes to the object.

Example:

Output:

The code shows how the Book object is passed by constant reference to the printBookDetails function by avoiding making unnecessary copies and making sure that the original object remains unchanged, which improves the code’s efficiency.

Method 5: Passing by Move (Using rvalue references)

Passing by move in C++ provides a function with the ability to take ownership of the resources of an object by using rvalue references, which is particularly useful for performance optimization of C++ programs by avoiding making unnecessary copies of large objects. When you pass an object by moving, it can be “moved from”, which means that its resources can be transferred to another object without leaving the original object in a valid but unspecified state.

Example:

Output:

The code shows how the String object is passed by a move to the processString function, which gives the ability to transfer ownership of its resources, and after the move, the original object is left in a valid but unspecified state. Here, std::move(str) is used to convert str into a value, which allows the move constructor to transfer ownership of its resources instead of copying.

Pass by Value vs Reference vs Pointer vs Move

Conclusion

Passing objects to functions in C++ is a basic yet important task that provides efficient manipulation of data inside the classes. As we have discussed above in this article, there are various methods for passing objects to functions, such as passing by value, by reference, by pointer, and by move. So, by understanding these methods and choosing the appropriate method accordingly, you can easily enhance your C++ code efficiency.

Explore the foundational topics and key concepts of C++ programming in the articles below:

C++ assignment operators – Demonstrates operator chaining and precedence.

Substring in C++ – Explains parameters: starting index and length.

Why are not variable length arrays part of the C++ standard? – Covers difference from C language VLAs.

Getline in C++ – Uses std::getline() with std::cin and file streams.

Array decay or array to pointer conversion in C++ – Highlights loss of array size information.

Read binary files in C++ – Explains byte-level access via buffers.

ifstream get in C++ – Allows reading whitespaces and newlines.

istream readsome in C++ – Doesn’t block like read() or getline().

Pass Objects to Functions in C++ – FAQs