C++ malloc()

The function malloc() in C++ is used to allocate the requested size of bytes and it returns a pointer to the first byte of allocated memory. A malloc() in C++ is a function that allocates memory at the runtime, hence, malloc() is a dynamic memory allocation technique. It returns a null pointer if fails.

Syntax:

pointer_name = (cast-type*) malloc(size);

Here, size is an unsigned integral value (cast to size_t) which represents the memory block in bytes

malloc() in C++ allocates a block of size bytes of memory, returning a pointer to the beginning of the block. The content of the newly allocated block of memory is not initialized, remaining with indeterminate values. Malloc function is present in <cstdlib> header file.

Return Types of malloc()

If the size is zero, the return value depends on the particular library implementation (it may or may not be a null pointer), but the returned pointer shall not be dereferenced.

• void pointer is used to the uninitialized the initialized memory block that is allocated by the function
• null pointer if the allocation fails

Working and Allocation of Memory Blocks Using malloc()

Example 1:

// C++ program to demonstrate working of malloc() // cstdlib is used to use malloc function #include <cstdlib> #include <iostream> using namespace std; int main() {  // size_t is an integer data type which can assign  // greater than or equal to 0 integer values  size_t s = 0; // s is SIZE  // malloc declaration/initialization  int* ptr = (int*)malloc(s);  // return condition if the memory block is not  // initialized  if (ptr == NULL) {  cout << "Null pointer has been returned";  }  // condition printing the message if the memory is  // initialized  else {  cout << "Memory has been allocated at address "  << ptr << endl;  }  free(ptr);  return 0; } 

Memory has been allocated at address 0x8cae70

free() function in C++ is used to dynamically de-allocate the memory.

Example 2:

// C++ program to demonstrate working of malloc() #include <iostream>  #include<stdlib.h>  using namespace std;    int main()  {   // variable declaration  int var_len = 10;    // pointer variable declaration  int *ptr;    // allocating memory to the pointer variable using malloc()  ptr = (int*) malloc(sizeof(int)*var_len);   for(int i=0;i<var_len;i++)   {   cout << "Enter a number : " << endl;   cin >> *(ptr+i);   }   cout << "Entered elements are : " << endl;   for(int i=0;i<var_len;i++)   {   cout << *(ptr+i) << endl;   }  free(ptr);   return 0;  } 

Output:

Where Should Malloc be used?

1. Dynamic Memory allocation

Dynamic Memory Allocation helps us allocate a piece of memory as per the user's demand. It returns a pointer to the start of that memory, which could be treated similarly to an array.

2. Heap memory

malloc() allocates the memory location on the heap and returns a pointer on the stack pointing to the starting address of the array type memory being allocated whereas the static array size put a hard upper limit on how much data the program could process at any one time, without being recompiled.

3. Better lifetime

Variables or Arrays created using malloc exist for a lifetime until they are cleared. This is of great importance for various data structures such as linked lists, binary heap, etc.

Difference between new and malloc()