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C++ Fundamentals for Professionals

- Examples

Explore practical examples of using smart pointers in C++ to manage dynamic memory safely. Understand how shared_ptr manages reference counting, how custom deleters work, and why weak_ptr is needed to break cyclic references. This lesson helps you apply smart pointers to avoid memory leaks and optimize resource handling.

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Example 1 #

To get a visual idea of the life cycle of the resource, there is a short message in the constructor and destructor of MyInt (lines 8 - 16).

C++
// sharedPtr.cpp
#include <iostream>
#include <memory>
using std::shared_ptr;
struct MyInt{
  MyInt(int v):val(v){
    std::cout << "  Hello: " << val << std::endl;
  }
  ~MyInt(){
    std::cout << "  Good Bye: " << val << std::endl;
  }
  int val;
};
int main(){
  std::cout << std::endl;
  shared_ptr<MyInt> sharPtr(new MyInt(1998));
  std::cout << "    My value: " << sharPtr->val << std::endl;
  std::cout << "sharedPtr.use_count(): " << sharPtr.use_count() << std::endl;
  {
    shared_ptr<MyInt> locSharPtr(sharPtr);
    std::cout << "locSharPtr.use_count(): " << locSharPtr.use_count() << std::endl;
  }
  std::cout << "sharPtr.use_count(): "<<  sharPtr.use_count() << std::endl;
  shared_ptr<MyInt> globSharPtr= sharPtr;
  std::cout << "sharPtr.use_count(): "<<  sharPtr.use_count() << std::endl;
  globSharPtr.reset();
  std::cout << "sharPtr.use_count(): "<<  sharPtr.use_count() << std::endl;
  sharPtr= shared_ptr<MyInt>(new MyInt(2011));
  std::cout << std::endl;
  
}

Explanation #

  • In line 22, we create MyInt(1998), which is the resource that the smart pointer should address. By using sharPtr->val, we have direct access to the resource (line 23).

  • The output of the program shows the number of references counted. ...