std::free (3) - Linux Manuals

std::free: std::free

NAME

std::free - std::free

Synopsis

Defined in header <cstdlib>
void free( void* ptr );

Deallocates the space previously allocated by std::malloc, std::calloc
, std::aligned_alloc
(since C++17), or std::realloc.
If ptr is a null pointer, the function does nothing.
The behavior is undefined if the value of ptr does not equal a value returned earlier by std::malloc, std::calloc
, std::aligned_alloc
(since C++17), or std::realloc.
The behavior is undefined if the memory area referred to by ptr has already been deallocated, that is, std::free or std::realloc has already been called with ptr as the argument and no calls to std::malloc, std::calloc
, std::aligned_alloc
(since C++17), or std::realloc resulted in a pointer equal to ptr afterwards.
The behavior is undefined if after std::free returns, an access is made through the pointer ptr (unless another allocation function happened to result in a pointer value equal to ptr)

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

ptr - pointer to the memory to deallocate

Return value

(none)

Notes

The function accepts (and does nothing with) the null pointer to reduce the amount of special-casing. Whether allocation succeeds or not, the pointer returned by an allocation function can be passed to std::free.

Example

// Run this code

  #include <cstdlib>

  int main()
  {
      int* p1 = (int*)std::malloc(10*sizeof *p1);
      std::free(p1); // every allocated pointer must be freed

      int* p2 = (int*)std::calloc(10, sizeof *p2);
      int* p3 = (int*)std::realloc(p2, 1000*sizeof *p3);
      if(p3) // p3 not null means p2 was freed by std::realloc
         std::free(p3);
      else // p3 null means p2 was not freed
         std::free(p2);
  }