Question

Currently Visual C++ is shipped with runtime where malloc() is decorated with __declspec( restrict ).

MSDN says this decoration states to the compiler that a pointer returned by malloc() cannot be aliased by any other pointer. Okay, two subsequent calls to malloc() indeed return distinct pointers. But what happens if I call

void* memory1 = malloc( 10 );
free( memory1 );
void* memory2 = malloc( 10 );
//here memory1 may be equal to memory2

In this case the two pointers can point to the very same location. How does this correlate with cannot be aliased by any other pointer implication of __declspec( restrict )?

Answer 1

The standard has this to say about “object lifetime” (§3.8 in N3290):

The lifetime of an object of type T ends when:
— if T is a class type with a non-trivial destructor (12.4), the destructor call starts, or
— the storage which the object occupies is reused or released.

After you’ve free‘d the block pointed to by memory1, that object is dead. It has ceased to exist. Dereferencing that pointer would be undefined behavior.

memory2 could be assigned the same memory address, but it wouldn’t “alias” anything: what was at that location has passed away.