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.

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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.

[ Note

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.

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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.

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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().