Introduction to C++ | malloc vs new

C++ malloc vs new

In C++, both malloc and new are used for memory allocation, but they serve different purposes and behave differently. While both can allocate memory dynamically, new is more suitable for C++ programs because it integrates with the object-oriented features of C++ and automatically handles object construction and destruction.

What is malloc?

malloc (memory allocation) is a standard library function from the C programming language, used to allocate a block of memory of a specified size on the heap. It returns a pointer to the allocated memory. If the memory allocation fails, it returns NULL.

Syntax of malloc:

        pointer = (dataType*) malloc(size_in_bytes);
                    

malloc does not initialize the allocated memory, meaning it may contain garbage values. To properly initialize the memory, you would need to use functions like memset.

What is new?

new is a C++ keyword that allocates memory on the heap for a single object or an array of objects. Unlike malloc, new initializes the memory and calls the constructor (for class objects). Additionally, new automatically returns a pointer of the correct type, eliminating the need for casting as required by malloc.

Syntax of new:

        pointer = new dataType; // Allocates memory for one element
        pointer = new dataType[size]; // Allocates memory for an array
                    

Differences between malloc and new

Example of malloc

The following example shows how to use malloc for dynamic memory allocation in C++:

        #include <iostream>
        #include <cstdlib> // for malloc
        using namespace std;
        
        int main() {
            // Dynamically allocate memory for an integer using malloc
            int* ptr = (int*) malloc(sizeof(int));
        
            if (ptr == NULL) {
                cout << "Memory allocation failed" << endl;
                return -1;
            }
        
            // Assign value to allocated memory
            *ptr = 10;
            cout << "Value: " << *ptr << endl;
        
            // Free the allocated memory
            free(ptr);
        
            return 0;
        }
                    

Output

Example of new

Here's an example that demonstrates how to use new for dynamic memory allocation:

        #include <iostream>
        using namespace std;
        
        int main() {
            // Dynamically allocate memory for an integer using new
            int* ptr = new int;
        
            // Assign value to allocated memory
            *ptr = 20;
            cout << "Value: " << *ptr << endl;
        
            // Free the allocated memory
            delete ptr;
        
            return 0;
        }
                    

Output

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