20 General utilities library [utilities]

20.10 Memory [memory]

20.10.12 C library memory allocation [c.malloc]

The header <cstdlib> ([cstdlib.syn]) declares the functions described in this subclause.
— end note]
void* aligned_alloc(size_t alignment, size_t size); void* calloc(size_t nmemb, size_t size); void* malloc(size_t size); void* realloc(void* ptr, size_t size);
Effects: These functions have the semantics specified in the C standard library.
Remarks: These functions do not attempt to allocate storage by calling ​::​operator new() ([new.delete]).
Storage allocated directly with these functions is implicitly declared reachable (see [basic.stc.dynamic.safety]) on allocation, ceases to be declared reachable on deallocation, and need not cease to be declared reachable as the result of an undeclare_­reachable() call.
This allows existing C libraries to remain unaffected by restrictions on pointers that are not safely derived, at the expense of providing far fewer garbage collection and leak detection options for malloc()-allocated objects.
It also allows malloc() to be implemented with a separate allocation arena, bypassing the normal declare_­reachable() implementation.
The above functions should never intentionally be used as a replacement for declare_­reachable(), and newly written code is strongly encouraged to treat memory allocated with these functions as though it were allocated with operator new.
— end note]
These functions implicitly create objects ([intro.object]) in the returned region of storage and return a pointer to a suitable created object.
In the case of calloc and realloc, the objects are created before the storage is zeroed or copied, respectively.
void free(void* ptr);
Effects: This function has the semantics specified in the C standard library.
Remarks: This function does not attempt to deallocate storage by calling ​::​operator delete().
See also: ISO C 7.22.3