malloc_usable_size() prototype

[Dizzzy_Dozzzer]

Hi, I've got a problem while trying to use the malloc_usable_size() function. The manual says that it's necessary to include <stdlib.h>, but including either <stdlib.h> or <cstdlib> has the same effect:

.../main.cpp | str# | error: 'malloc_usable_size' was not declared in this scope

Where's the prototype of this function? I'm using Code::Blocks 10.05, FreeBSD 9.1.

Thank you.

 

[expl]

Its defined in malloc_np.h, reason why its not included in stdlib.h is unknown to me, but an educated guess would be its because malloc_usable_size is not included in POSIX.x or C90/99.