Dictionary allocation is a stack-oriented allocation scheme, i.e., if you want to deallocate X, you also deallocate everything allocated after X.
The allocations using the words below are contiguous and grow the region
towards increasing addresses. Other words that allocate dictionary
memory of any kind (i.e., defining words including
the contiguous region and start a new one.
In ANS Forth only
created words are guaranteed to produce an
address that is the start of the following contiguous region. In
particular, the cell allocated by
variable is not guaranteed to
be contiguous with following
You can deallocate memory by using
allot with a negative argument
(with some restrictions, see
allot). For larger deallocations use
here– addr core “here”
Return the address of the next free location in data space.
unused– u core-ext “unused”
Return the amount of free space remaining (in address units) in
the region addressed by
allotn – core “allot”
Reserve n address units of data space without initialization. n is a signed number, passing a negative n releases memory. In ANS Forth you can only deallocate memory from the current contiguous region in this way. In Gforth you can deallocate anything in this way but named words. The system does not check this restriction.
c,c – core “c-comma”
Reserve data space for one char and store c in the space.
f,f – gforth “f,”
Reserve data space for one floating-point number and store f in the space.
,w – core “comma”
Reserve data space for one cell and store w in the space.
2,w1 w2 – gforth “2,”
Reserve data space for two cells and store the double w1 w2 there, w2 first (lower address).
Memory accesses have to be aligned (see Address arithmetic). So of
course you should allocate memory in an aligned way, too. I.e., before
allocating allocating a cell,
here must be cell-aligned, etc.
The words below align
here if it is not already. Basically it is
only already aligned for a type, if the last allocation was a multiple
of the size of this type and if
here was aligned for this type
createing a word,
ANS Forth (
maxaligned in Gforth).
align– core “align”
If the data-space pointer is not aligned, reserve enough space to align it.
falign– float “f-align”
If the data-space pointer is not float-aligned, reserve enough space to align it.
sfalign– float-ext “s-f-align”
If the data-space pointer is not single-float-aligned, reserve enough space to align it.
dfalign– float-ext “d-f-align”
If the data-space pointer is not double-float-aligned, reserve enough space to align it.
maxalign– gforth “maxalign”
Align data-space pointer for all alignment requirements.
cfalign– gforth “cfalign”
Align data-space pointer for code field requirements (i.e., such that the corresponding body is maxaligned).