AutosarC++18_03-A18.5.10

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

Required inputs: IR

Placement new constructs an object at a specific memory address. The memory must be properly aligned for the object type and have sufficient size. Misaligned storage or insufficient space causes undefined behavior, memory corruption, and crashes. Array new also requires space for array cookies that many implementations use to track array size.

Bad code (insufficient storage):

char buffer[2];  // ERROR: too small for int
int* ptr = new (buffer) int(42);  // Undefined behavior: buffer overflow

Bad code (misalignment):

char data[sizeof(double) + 1];
double* ptr = new (data + 1) double(3.14);  // ERROR: misaligned

Good code (sufficient aligned storage):

alignas(int) char buffer[sizeof(int)];      // OK: properly aligned
int* ptr = new (buffer) int(42);

Good code (using std::aligned_storage):

std::aligned_storage::type storage;
MyClass* ptr = new (&storage) MyClass();    // OK: correct alignment and size

Good code (array placement with cookies):

// Account for array cookie overhead (typically pointer-sized)
const size_t array_size = 10;
const size_t overhead = sizeof(size_t);     // Array cookie space
char buffer[array_size * sizeof(int) + overhead];
int* arr = new (buffer) int[array_size];    // OK: includes cookie space

Possible Messages

Key	Text	Severity	Disabled
array_new	Ensure to account for the overhead of array new expressions, i.e., storage required for array cookies	None	False
improper_alignment	Improper alignment {} when using placement new operator, intended storage has alignment {}	None	False
insufficient_storage	Insufficient space when using placement new operator: Object has {} bits, intended storage has {} bits	None	False

Options

• This rule shares the following common options: exclude_in_macros, exclude_messages_in_system_headers, excludes, extend_exclude_to_macro_invocations, includes, justification_checker, languages, post_processing, provider, report_at, severity

• The following places define options that affect this rule: Stylechecks, Analysis-GlobalOptions

check_array_cookies

check_array_cookies : bool = False

Check if storage space for array cookies is missing (needs StaticSemanticAnalysis).