HP 3000 Manuals HP 3000 Manuals
Transfer Procedures
The transfer procedures supported by HP Pascal are pack and unpack. A
description of these procedures follows.
pack
Usage
pack(a, i, z)
Parameters
a Any ARRAY [m..n] of t.
i An expression that is type compatible with the index of the
non-packed array.
z Any PACKED ARRAY [u..v] of t.
Description
The standard procedure pack transfers data from unpacked arrays to packed
arrays. For example, assuming that a is an ARRAY[m..n] OF t and z is a
PACKED ARRAY[u..v] of t; the procedure pack(a, i, z) assigns components
of the unpacked array a, starting at component i, to each component of
the packed array z.
Because all the components of z are assigned a value, the normalized
value of i must be less than or equal to the difference between the
lengths of a and z + 1; for example, i-m+1 <= (n-m) - (v-u) + 1.
Otherwise, it is an error when pack attempts to access a nonexistent
component of a.
The component types of arrays a and z must be type identical. The index
types of a and z, however, may be incompatible.
The call pack(a, i, z) is equivalent to:
BEGIN
k:= i;
FOR j:= u TO v DO
BEGIN
z[j]:= a[k];
IF j <> v THEN k:= succ(k);
END;
END;
where k and j are variables that are type compatible with the index type
of a and the index type of z, respectively.
Example
PROGRAM show_pack (input,output);
TYPE
clothes = (hat, glove, shirt, tie, sock);
VAR
dis : ARRAY [1..10] OF clothes;
box : PACKED ARRAY [1..5] of clothes;
index: integer;
.
.
BEGIN
.
.
index:= 1;
pack(dis,index,box); { After pack executes, box contains }
. { the first 5 components of dis. }
.
index:= 8;
pack(dis,index,box); { An error results when pack attempts }
. { to access nonexistent 11th component }
. { of dis. }
END.
unpack
Usage
unpack(z, a, i)
Parameters
z Any PACKED ARRAY [u..v] of t.
a Any ARRAY [m..n] of t.
i An expression that is type compatible with the index of the
non-packed array.
Description
This procedure transfers data from a packed array to an unpacked array.
For example, assuming that a is an ARRAY[m..n] OF t and z is a PACKED
ARRAY [u..v] OF t; the procedure unpack(z,a,i) successively assigns the
components of the packed array z, starting at component u, to the
components of the unpacked array a, starting at a [ i ].
All the components of z are assigned. Also, the normalized value of i
must be less than or equal to the difference between the lengths of a and
z + 1; for example, i-m+1 <= (n-m) - (v-u) + 1. Otherwise, it is an
error when unpack attempts to index a beyond its upper bound.
The index types of a and z need not be compatible. The components of the
two arrays, however, must be type identical.
The call unpack(z,a,i) is equivalent to:
BEGIN
k:= i;
FOR j:= u TO v DO
BEGIN
a[k]:= z[j];
IF j <> v THEN k:= succ(k);
END;
END;
where k and j are variables that are type compatible with the indices of
a and z respectively.
Example
PROGRAM show_unpack (input,output);
TYPE
suit_types = (casual, business, leisure, birthday);
VAR
suit : PACKED ARRAY [1..5] OF suit_types;
kase : ARRAY [1..10] OF suit_types;
i : integer;
.
.
BEGIN
.
.
i := 1;
unpack(suit,kase,i); { After execution, the first 5 }
. { components of kase contain the }
. { value of suit. }
.
i := 7
unpack(suit,kase,i); { An error results because unpack }
. { attempts to assign a component of }
. { suit to a component of kase which }
. { is out of range. }
END.