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std::calloc(3)		       C++ Standard Libary		  std::calloc(3)

NAME
     std::calloc - std::calloc

Synopsis
	Defined in header <cstdlib>
	void* calloc( std::size_t num, std::size_t size );

	Allocates  memory  for an array of num objects of size size, initializes
     it to all
	bits zero (implicitly creating objects in the destination area).

	If allocation succeeds, returns a pointer to the lowest (first) byte  in
     the
	allocated memory block that is suitably aligned for any object type.

	If  size  is  zero, the behavior is implementation defined (null pointer
     may be
	returned, or some non-null pointer may be returned that may not be  used
     to access
	storage).

	The following functions are required to be thread-safe:

	  * The library versions of operator new and operator delete
	  * User replacement versions of global operator new and operator
	    delete
	  *	      std::calloc,	     std::malloc,	    std::realloc
     (since C++11)
	    , std::aligned_alloc
	    (since C++17), std::free

	Calls to these functions that allocate or deallocate a particular unit
	of storage occur in a single total order, and each such deallocation
	call happens-before the next allocation (if any) in this order.

Parameters
	num  - number of objects
	size - size of each object

Return value
	On success, returns the pointer to the beginning of newly allocated mem-
     ory. To avoid
	a memory leak, the returned pointer must be deallocated with std::free()
     or
	std::realloc().

	On failure, returns a null pointer.

Notes
	Due to the alignment requirements, the number of allocated bytes is  not
     necessarily
	equal to num * size.

	Initialization to all bits zero does not guarantee that a floating-point
     or a
	pointer  would be initialized to 0.0 and the null pointer value, respec-
     tively
	(although that is true on all common platforms).

	Originally (in C89), support for zero size was added to accommodate code
     such as

      OBJ *p = calloc(0, sizeof(OBJ)); // "zero-length" placeholder
      ...
      while (1)
      {
	  p = realloc(p, c * sizeof(OBJ)); // reallocations until size settles
	  ... // code that may change c or break out of loop
      }

Example
     // Run this code

      #include <cstdlib>
      #include <iostream>

      int main()
      {
	  int* p1 = (int*)std::calloc(4, sizeof(int)); // allocate and zero  out
     an array of 4 int
	  int*	p2  =  (int*)std::calloc(1, sizeof(int[4])); // same, naming the
     array type directly
	  int* p3 = (int*)std::calloc(4, sizeof *p3); // same, without repeating
     the type name

	  if (p2)
	      for (int n = 0; n < 4; ++n) // print the array
		  std::cout << "p2[" << n << "] == " << p2[n] << '\n';

	  std::free(p1);
	  std::free(p2);
	  std::free(p3);
      }

Output:
      p2[0] == 0
      p2[1] == 0
      p2[2] == 0
      p2[3] == 0

See also
	C documentation for
	calloc

http://cppreference.com 	   2024.06.10			  std::calloc(3)
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