Datasheet

The C and C++ Libraries

• your memory model can supply a block of memory at a lower address than the

first one supplied.

If you know in advance that the address space bounds of your heap are small, you do

not have to redefine

__user_heap_extent()

, but it does speed up the heap algorithms if

you do.

The input parameters are the default values that are used if this routine is not defined.

You can, for example, leave the default base value unchanged and only adjust the size.

Note

The size field returned must be a power of two. If you return zero for

size

, the heap

extent is set to 4GB.

Using a heap implementation from bare machine C

To use a heap implementation in an application that does not define

main()

and does not

initialize the C library:

1. Call

_init_alloc(base, top)

to define the base and top of the memory you want

to manage as a heap.

2. Define the function

unsigned __rt_heap_extend(unsigned size, void ** block)

to handle calls to extend the heap when it becomes full.

alloca()

behaves identically to

malloc()

except that

alloca()

has automatic garbage

collection (see alloca() on page 4-101).