A18-5-10 - Unofficial Autosar C++ Guidelines Reference

Rule A18-5-10 (required, implementation, automated)

Placement new shall be used only with properly aligned pointers to sufficient storage capacity.

Rationale

Placement new can be useful for cases in which allocation is required separately from type initialization, e.g. memory allocators, generic containers. Correct usage of placement new requires passing a pointer that: is suitably aligned provides sufficient storage memory Violating above constrains will result in an object constructed at a misaligned location or memory initialization outside of the allocated bounds, which leads to undefined behaviour. An initial memory pointer used for placement new shall not be used after the call.

Example

//% $Id: A18-5-10.cpp 305629 2018-01-29 13:29:25Z piotr.serwa $

#include <new>
#include <cstdint>

void Foo()
{
uint8_t c;
uint64_t* ptr = ::new (&c) uint64_t;

//non-compliant, insufficient storage
}

void Bar()
{
uint8_t c; // Used elsewhere in the function
uint8_t buf[sizeof(uint64_t)];
uint64_t* ptr = ::new (buf) uint64_t;

//non-compliant, storage not properly aligned
}

Rationale

Providing a custom allocation function (operator new) for a class or program implies the use of a custom memory management scheme different to the default one. It is therefore unlikely that memory allocated using a custom allocation function can be deallocated by the default deallocation function (operator delete).

Example

//% $Id: A18-5-11.cpp 316977 2018-04-20 12:37:31Z christof.meerwald $
#include <cstdlib>

class A {
public:
static void * operator new(std::size_t s); // Compliant: operator new

static void operator delete(void *ptr);

// defined together with
// operator delete

};

class B {
public:

static void * operator new(std::size_t s);

// Non-compliant: operator

static void * operator new [](std::size_t s); // new defined without

// corresponding operator
// delete

};

Unofficial Autosar C++ Guidelines Reference

Rationale

Example

See also

Rationale

Example

See also