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C++

C++ Memory Management : New and Delete Operators

Written by Rahul Lath

Updated on: 17 Aug 2023

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C++ Memory Management is a crucial aspect of programming in C++. There are various mechanisms for  memory allocation in C++ including automatic, static and dynamic memory allocation.

Automatic memory allocation is done for local variables and is performed automatically by the compiler. Static memory allocation is done for global variables and is allocated at compile-time. 

Dynamic memory allocation is done using operators such as new and delete or malloc and free and is allocated at run-time.Dynamic memory allocation or dynamic allocation in c++ allows for more flexibility in managing memory, but also requires careful handling to avoid memory leaks and other issues. 

Memory leaks occur when memory that has been allocated is not properly deallocated, leading to a loss of available memory and potential program crashes.

To avoid memory leaks, it is important that we manage memory using techniques such as smart pointers, that can automatically manage the lifetime of dynamically allocated objects, or garbage collection, which automatically frees memory that is no longer needed.

Overall, we are going to discuss how C++ memory management is an essential aspect of programming, and proper management of memory can greatly improve the stability and performance of your programs.

What is Memory Management?

C++ Memory management is a critical aspect of programming. It refers to the process of allocating and deallocating memory for variables, objects, and other data structures used in a program. In C++ memory management can be done explicitly using the new and delete operators that we are going to explore later in thai article.

Why do we need memory management in C++?

C++ is a statically typed language, which means that some variables that we are going to be using in our program have to be declared along with their data types at compile time. This makes it challenging to allocate memory for variables whose size or type is not known until runtime. In C++ memory management does not automatically manage memory for objects, which can lead to memory leaks and other issues if memory is not properly allocated and deallocated which is why it is important we understand memory allocation in C++.

Basics of the C++ memory model

C++ memory management is divided into two primary areas: the stack and the heap. The stack is used for static memory allocation, where memory is allocated and deallocated automatically by the compiler itself.The heap is used for dynamic allocation in C++, where the memory can be  allocated and deallocated explicitly by the programmer as opposed to the compiler in stack.

Allocation and Deallocation of Memory

C++ provides two operators for dynamically allocating and deallocating memory: new and delete. These operators are used to allocate and deallocate memory for objects at runtime to avoid memory leaks and efficiently manage the memory.

C++ New Operator

The new operator is used to allocate memory for an object on the heap. 

Lets see the syntax for the new operator:

int* ptr = new int;

In the example above we can see that the new operator allocates memory for an integer on the heap and returns a pointer to the allocated memory. This pointer is then assigned to the variable ptr, which can be used to access the allocated memory.

It’s important to note that the new operator may throw a bad_alloc exception if the requested memory cant be allocated for some reason. Therefore, it’s always a good practice as a programmer to check the return value of new to ensure that memory has been successfully allocated before using the allocated memory, to avoid any complications further in your code.

C++ Delete Operator

The delete operator is used to deallocate memory that was previously allocated using the new operator. The syntax for the delete operator is as follows:

delete ptr;

In the above example, the delete operator deallocates the memory pointed to by the pointer variable ptr. It’s important to note that delete should only be used to deallocate memory that was previously allocated using new. Attempting to delete memory that was not allocated using new can result in undefined behavior and throw errors/exceptions.

New and Delete Operator for Arrays:

In C++, dynamic arrays can be allocated using the new operator and deallocated using the delete operator. The new operator returns a pointer to the first element of the array, and the delete operator frees the memory allocated for the array. Here is an example:

int n = 10; int* arr = new int[n]; // allocate an array of size n // use the array delete[] arr; // deallocate the array

Note that when deallocating a dynamic array, the delete operator must be used with square brackets [] to indicate that an array is being deallocated.

New and Delete Operator for Objects:

In C++, dynamic objects can also be allocated using the new operator and deallocated using the delete operator. Here is an example:

class MyClass { public: MyClass() { /* constructor */ } ~MyClass() { /* destructor */ } void foo() { /* class method */ } }; MyClass* obj = new MyClass(); // allocate a new object obj->foo(); // use the object delete obj; // deallocate the object

Note that when deallocating a dynamic object, the delete operator must be used without square brackets [].

Common Memory Management Bugs:

We need to try and prevent bugs and errors in our code as much as possible as they will avalanche into bigger errors later in our program.So lets see some common memory management bugs include:

  • Memory leaks: When memory is allocated but not deallocated, leading to a loss of available memory and potential program crashes.
  • Dangling pointers: When a pointer points to memory that has been deallocated, leading to undefined behavior.
  • Double free: When memory is deallocated more than once, leading to undefined behavior.

Preventing Bugs with Smart Pointers:

Smart pointers are a type of C++ object that automatically manage the lifetime of dynamically allocated objects, preventing memory leaks and other common memory management bugs. Here is an example:

#include <memory> class MyClass { public: MyClass() { /* constructor */ } ~MyClass() { /* destructor */ } void foo() { /* class method */ } }; std::unique_ptr<MyClass> ptr(new MyClass()); // allocate a new object ptr->foo(); // use the object // no need to deallocate the object manually

Conclusion

Memory management is a critical aspect of programming in C++. In C++, memory is managed using automatic, static, and dynamic memory allocation mechanisms. Dynamic memory allocation provides the most flexibility but requires careful handling to avoid memory leaks and other issues.

Memory leaks and other common memory management bugs, such as dangling pointers and double-free, can lead to program crashes and other unexpected behavior. To avoid these issues, it is essential to properly manage memory using techniques such as smart pointers, which automatically manage the lifetime of dynamically allocated objects.

Smart pointers, such as unique_ptr and shared_ptr, are powerful tools for managing memory in C++. They prevent memory leaks and other common memory management bugs by automatically deallocating memory when it is no longer needed. Smart pointers are easy to use and integrate seamlessly with modern C++ code.

Overall, proper memory management is essential for building stable and efficient C++ programs. By understanding the different memory management techniques available in C++ and using smart pointers to manage dynamic memory, developers can avoid common memory management bugs and ensure their programs run smoothly and reliably.

FAQS

What are the Advantages of New Operator Over Malloc Function?

The new operator in C++ provides several advantages over the malloc function. The new operator automatically calls the constructor of the object being allocated, while malloc does not. Additionally, new returns a pointer to the correct type of object, while malloc returns a void pointer that must be cast to the correct type. Finally, new can throw an exception if the allocation fails, while malloc returns a null pointer.

What is the difference between Unique pointers and Shared Pointers?

Unique pointers and shared pointers are both types of smart pointers in C++. The main difference between them is that unique pointers are used to manage ownership of a single object, while shared pointers can be used to manage ownership of multiple objects. Unique pointers cannot be copied, while shared pointers can be copied and shared among multiple owners. Unique pointers use move semantics to transfer ownership, while shared pointers use reference counting.

What are the three parts in C++ program’s memory?

A C++ program’s memory can be divided into three parts: the stack, the heap, and the code segment. The stack is used to store function call frames and local variables. The heap is used to store dynamically allocated objects. The code segment is used to store the program’s executable code. The stack and heap grow in opposite directions, with the stack growing downward and the heap growing upward. The code segment is read-only and cannot be modified at runtime.

Written by

Rahul Lath

Reviewed by

Arpit Rankwar

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