Malloc() and new in C++

In C ++, malloc () and new are used for the same thing. During runtime, they are used to allocate memory. Malloc () and the new, on the other hand, have different syntax. The basic difference between malloc () and new is that new is the operator, whereas malloc () is the default standard library function in the stdlib header file.

What do you mean by new?

New is a memory allocation operator used at runtime for memory allocation. The heap stores the memory allocated by the new operator. It returns the initial address of the memory, which is then allocated to the variable. The new operator in C ++ is similar to the malloc () function in C programming language in terms of functionality. Although the malloc () method is also compatible with C ++, newer operators are more commonly used because of its advantages.

type_variable = new type(parameter_list); //syntax

Explanation:

• Specifies the data type of this variable for which new operators are allocating memory.
• The name of the variable that points to memory is a variable.
• The parameter list is a list of initialized values for a variable.

The sizeof () operator is not used to allocate memory by the new operator. It also avoids using the resize operator as the new operator creates enough memory for the object. It is a structure that calls the object () {[original code]} function to initialize the object at the moment of declaration. Because the new operator allocates memory in the heap, an exception is thrown out if the new operator tries to allocate it, but no memory is available in the heap. If our code is unable to handle the exception, the application will terminate unexpectedly.

Example of a program containing new operator in C++:

#include <iostream>
#include <stdlib.h>
#include <bits/stdc++.h>  
using namespace std;  
int main()  
{  
 int *A;  // integer pointer variable declaration  
 A=new int; // allocating memory to the pointer variable A.  
 std::cout << "Еnter the number : " << std::endl;  
 std::cin >>*A;  
 std::cout << "Еntered number is " <<*A<< std::endl;  
 return 0;  
}  

OUTPUT:

enter number : 10
entered number is 10
……….Program finished with exit code 0
Press any key to continue

Explanation:

In the above example a pointer variable of type int is initialized and new operator is allocating memory to the pointer variable A.

What do you mean by malloc() ?

A malloc() function is a runtime memory allocation function. This method returns a void pointer, which may be given to any kind of pointer. This void pointer can be typecast to get a pointer that refers to a certain type of memory.

type variable_name = (type *)malloc(sizeof(type));  //syntax

Explanation:

• The data type of the variable for which memory must be allocated is called type.
• Variable name Specifies the name of the memory-pointing variable.
• 'type*' is used for typecasting, which allows us to get a given type of pointer pointing towards memory.
• The malloc () method uses the sizeof () operator to determine the amount of memory required for allocation.

Important: To give the pointer a new type, typecasting is required because the malloc () operation returns the void pointer. Because the malloc () method returns raw memory, the sizeof () operator is required in the malloc () function to indicate how much memory is required for allocating the malloc () function.

Example of a program showing how to malloc() function works:

#include <iostream> 
#include <bits/stdc++.h> 
#include<stdlib.h>  
using namespace std;  
int main()  
{  
  int length;   // variable declaration  
  std::cout << "Еnter the count of numbers: " << std::endl;  
  std::cin >> length;  
  int *A; // pointer variable declaration  
  A=(int*) malloc(sizeof(int)*length);  // allocating memory to  the poiner variable  
  for(int i=0;i<length;i++)  
  {  
      std::cout << "Еnter a number: " << std::endl;  
      std::cin >> *(A+i);  
  }  
  std::cout << "Еntered elements are : " << std::endl;  
   for(int i=0;i<length;i++)  
  {  
     std::cout << *(A+i) << std::endl;  
  }  
free(A);  
    return 0;  
}  

OUTPUT:

enter the count of numbers: 5
enter a number: 12
enter a number: 14
enter a number: 18
enter a number: 17
enter a number: 10
entered elements are: 
12
14
18
17
10
……….Program finished with exit code 0
Press any key to continue

If the free() method is not used correctly, it might result in a hanging reference. Such case example is given below:

#include <iostream>  
#include<stdlib.h>  
using namespace std;  
int *function()  
{  
    int *A;  
    A=(int*) malloc(sizeof(int));  
    free(A);  
    return A;  
}  
int main()  
{  
 int *A;  
 A=function();  
 free(A);  
    return 0;  
}

Explanation:

The function () function is called in the above code. Integer is returned by the pointer function () function. We have declared a * A pointer within the function () method and memory is allocated to this pointer variable using the malloc () function. In this example, we are returning a pointer that has already been freed from memory. Because it points to the free memory address, A is the swinging pointer. Alternatively, we can argue that A refers to memory that is not specified by the pointer.