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Message Passing in C++

Last Updated on August 18, 2023 by Mayank Dham

In the realm of object-oriented programming, the concept of communication between objects is pivotal for building robust and modular software systems. One of the fundamental mechanisms facilitating this communication is message passing. Derived from the principles of encapsulation and interaction, message passing allows objects to interact by invoking methods or functions on each other. Message passing in C++ is the exchange of information between two or more objects via a logical entity known as a message. In this section, we will discuss what is message passing in C++ with examples of message passing in c++, and the Difference between message passing and method calls.

What is Message Passing in C++?

Message passing in C++ involves passing objects or data between different parts of a program using functions, methods, or message queues. Objects communicate by sending and receiving data. A message for an object is a request for the execution of a procedure, and as such, it will invoke a function in the receiving object that produces the desired results. Message passing entails specifying the object’s name, the function’s name, and the data to be sent.

Example of Message Passing in C++

Message passing in c++ typically involves passing objects or data between different parts of a program using functions, methods, or message queues. Let’s see a message passing in c++ with example to understand it more clearly.

#include <iostream>
#include <string>
#include <queue>

class Message {
    std::string content;
    int priority;

    Message(std::string content, int priority) {
        this->content = content;
        this->priority = priority;

class MessageQueue {
    std::queue<Message> messages;

    void push(Message message) {

    Message pop() {
        Message message = messages.front();
        return message;

    bool isEmpty() {
        return messages.empty();

class MessageHandler {
    MessageQueue queue;

    void handleMessage() {
        while (!queue.isEmpty()) {
            Message message = queue.pop();
            std::cout << "Received message: " << message.content << std::endl;

    void sendMessage(std::string content, int priority) {
        Message message(content, priority);

int main() {
    MessageHandler handler;

    handler.sendMessage("Hello world", 1);
    handler.sendMessage("How are you?", 2);
    handler.sendMessage("Goodbye", 3);


    return 0;


Received message: Hello world
Received message: How are you?
Received message: Goodbye

In this example, the Message class represents a message to be passed between parts of the program. The MessageQueue class is a container for messages, which can be pushed and popped from the queue. The MessageHandler class is responsible for handling messages, receiving them from the queue, and processing them.
In the main() function, three messages are sent to the MessageHandler using the sendMessage() method. The handleMessage() method is then called to process the messages.

Here’s how the message passing works in detail:

  1. The main() function creates a MessageHandler object.
  2. Three messages are sent to the MessageHandler using the sendMessage() method. Each message has a string content and a priority level.
  3. The handleMessage() method is called to process the messages.
  4. The while loop runs until the message queue is empty.
  5. The pop() method is called to remove the next message from the queue.
  6. The content of the message is printed to the console.
  7. Steps 5-6 are repeated until the queue is empty.

The message queue allows messages to be stored and processed in the order they are received, while the message handler provides a way to handle messages and perform actions based on their content.

What are Message Queues in C++?

A message queue is a data structure that allows multiple processes or threads to communicate with each other by passing messages. It can be implemented using the standard library’s std::queue or a third-party library such as Boost. A message queue is a mechanism for sending and receiving messages, which are typically objects.

Difference between Message Passing and Method Call

Here we have the difference between message passing in c++ and method call:

Method call Message Passing
Method call is invoking a method on an  object Message passing is sending a message to an object
Syantax for method call is Object.method() Syntax of message passing is  Object->message()
It is procedural programming It is object-oriented programming
Execution is Synchronous Execution can be synchronous and asynchronous
Runtime efficiency is generally faster It can be slower due to message passing overhead
Method can access instance variables and state Message passing can encapsulate both data and behavior of an object
It is Supported in most language It more commonly used in OOP languages
It passed as argument It encapsulated within the message

In the realm of modern software development, effective communication between objects is paramount for building flexible and maintainable systems. Message passing, a core principle of object-oriented programming, provides a dynamic and organized approach to achieving this communication. Through this exploration, we’ve delved into the intricacies of message passing in C++, uncovering its significance in facilitating object interactions. By understanding its principles, advantages, and practical implementation, developers can harness the power of message passing to create modular, scalable, and collaborative software systems. As you continue your journey in the realm of C++ programming, keep in mind that mastering message passing opens up avenues for crafting elegant solutions that seamlessly weave together different components into a harmonious whole.

Frequently Asked Questions Related to message passing in c++

Here are the list of FAQs related to message passing in c++ with examples.
Q1: What exactly is message passing in C++?
Message passing in C++ refers to the mechanism through which objects interact by sending messages in the form of method or function calls. It facilitates communication and collaboration between objects to achieve desired outcomes.

Q2: How is message passing different from function calls?
While message passing and function calls both involve invoking methods or functions, message passing is more aligned with the concept of objects communicating to perform actions or exchange information. It emphasizes the encapsulation of behavior within objects.

Q3: Is message passing only applicable to C++ classes?
No, message passing can be applied to various object-oriented paradigms, including classes in C++. It’s a concept that spans multiple programming languages and methodologies.

Q4: Can you provide an example of message passing in C++?
Certainly! Consider a scenario where an "Order" object communicates with a "Customer" object. The Order object may send a message (method call) to the Customer object to update its order history. This interaction demonstrates message passing between objects.

Q5: How does message passing contribute to software design?
Message passing promotes modularity and encapsulation, leading to cleaner, more organized software designs. It enables objects to maintain their integrity while collaborating with others to fulfill complex tasks.

Q6: Is message passing efficient in terms of performance?
Message passing, like any mechanism, incurs some performance overhead due to function calls and context switches. However, its benefits in terms of code organization and maintainability often outweigh these minor performance considerations.

Q7: Can message passing replace other forms of communication between objects?
Message passing is a powerful form of communication, but it may not be suitable for all scenarios. In some cases, direct method calls or shared data might be more appropriate. The choice depends on the specific requirements of your program.

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