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Master Software Design Patterns and Architecture in C++

RAII Idiom Example

Explore the RAII idiom in C++ by examining an example that shows how resource acquisition is managed using constructors and destructors. Understand how objects release resources automatically when going out of scope, ensuring safe and efficient resource handling.

We'll cover the following...

Example

In this lesson, we’ll take a look at an example and see how a destructor is called when the resource goes out of scope. Let’s look at its code.

Code

C++
#include <iostream>
#include <new>
#include <string>
class ResourceGuard{
  private:
    const std::string resource;
  public:
    ResourceGuard(const std::string& res):resource(res){
      std::cout << "Acquire the " << resource << "." <<  '\n';
    }
    ~ResourceGuard(){
      std::cout << "Release the "<< resource << "." << '\n';
    }
};
int main(){
  std::cout << '\n';
  ResourceGuard resGuard1{"memoryBlock1"};
  std::cout << "\nBefore local scope" << '\n';
  {
    ResourceGuard resGuard2{"memoryBlock2"};
  }
  std::cout << "After local scope" << '\n';
  
  std::cout << '\n';
  
  std::cout << "\nBefore try-catch block" << '\n';
  try{
      ResourceGuard resGuard3{"memoryBlock3"};
      throw std::bad_alloc();
  }   
  catch (std::bad_alloc& e){
      std::cout << e.what();
  }
  std::cout << "\nAfter try-catch block" << '\n';
  
  std::cout << '\n';
}

Code explanation

Let’s look at the explanation of the code ...