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PDLLSPEC.TXT
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1992-07-08
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Writing Dynamic Link Libraries
for
The Windows ASPECT Script Language
Pascal Language Interface Specification
Introduction
PROCOMM PLUS for Windows implements a powerful scripting language called the
Windows ASPECT Script Language (ASPECT). One of ASPECT's great strengths is the ability
to call functions embedded in Dynamic Link Libraries (or DLLs) written and compiled outside of
ASPECT. This paper focuses on the writing of DLLs for ASPECT using Turbo Pascal* for
Windows* (TPW) from Borland International, Inc.
ASPECT to DLL Parameter Sequence
ASPECT generates a standard parameter block for every DLL call that it makes. This
standard parameter block has five parameters, listed in order below. When writing a DLL to be
called from ASPECT, every exported function that is to be accessible from within ASPECT
should declare exactly these number and types of parameters:
1. [HWnd] - a handle to the PROCOMM PLUS for Windows main window.
2. [THandle] - a handle to the instance of PROCOMM PLUS for Windows that made
the DLL call.
3. [pointer to array[0..9] of pointer] - a pointer to an array of pointers to the data
elements listed as parameters on the ASPECT script line that called the DLL
function.
4. [pointer to array[0..9] of byte] - a pointer to an array of bytes. Byte N of this
array describes the type of element N stored in the array of data elements (i.e.
parameter 3). The range of values in this array follows:
Byte
Value Meaning
0 nth element is an ASPECT string
1 nth element is an ASPECT integer
2 nth element is an ASPECT long
3 nth element is an ASPECT float
5. [int] - an integer containing the count of parameters provided on the ASPECT
script line calling the DLL function.
An Example
Below is the code for a DLL with a function that generates a random number. Under a
PASCAL style, stack-based parameter passing scheme, a variable number of parameters is not
normally possible; however, ASPECT provides an array-based parameter passing scheme as
described by the parameter block above. To demonstrate the ability to pass a variable number of
parameters, the DLL function listed below makes certain assumptions about the provided
parameters based on the number of parameters that are available:
1. If two parameters are passed to the DLL function:
a. the first parameter holds a long integer for seeding the random-number
generator.
b. the second parameter will hold the return value (i.e. the random number).
2. If one parameter is passed to the DLL function:
a. the DLL function should seed the random number generator using
Randomize function (from the TPW System Unit).
b. the single parameter will hold the return value (i.e. the random number).
Here is the code for the DLL. This is RANDINT.PAS:
library RandInt;
uses WinTypes;
const
IntegerType = 1;
LongType = 2;
MaxWord: Word = 65535;
type
pdatptrary = ^tdatptrary;
tdatptrary = array[0..9] of pointer;
ptypptrary = ^ttypptrary;
ttypptrary = array[0..9] of byte;
function RandomInt(PWWnd: HWnd; PWInst: THandle; PData: pdatptrary;
PType: ptypptrary; argcnt: integer): BOOL; export;
begin
if (argcnt < 1) then
begin {at least one arg?}
RandomInt := FALSE; {if not, return failure to Aspect}
exit;
end;
if (argcnt > 1) then
begin
if ((PType^[0] <> LongType) or (PType^[1] <> IntegerType)) then
begin
RandomInt := FALSE; {for two args, 1=long, 2=int}
exit; {if not, return failure to Aspect}
end;
RandSeed := PLongint(PData^[0])^; {seed generator}
PWord(PData^[1])^ := Random(MaxWord); {get the random number}
end
else
begin
if (PType^[0] <> IntegerType) then
begin
RandomInt := False; {for one arg, 1=int}
exit; {if not, return failure to Aspect}
end;
Randomize; {seed generator with time}
PWord(PData^[0])^ := Random(MaxWord); {get the random number}
end;
RandomInt := True; {return success to aspect}
end;
exports
RandomInt index 1;
begin
end.
Here is an ASPECT script using the DLL. This is RANDINT.WAS:
;ASPECT script demonstrating RANDINT.DLL
integer hdll, rnum
long seed = 1060665
proc cleanup
dllfree hdll
exit
endproc
proc main
string DLLPATH = "C:\PROWIN\ASPECT\RANDINT.DLL" ;path to the DLL
when userexit call cleanup ;point to cleanup routine
dllload DLLPATH hdll ;load the DLL
if (failure)
usermsg "dllload failed"
exit
endif
;generate a random number letting the DLL use system time as seed
dllcall hdll "RandomInt" rNum
if (failure)
usermsg "RandomInt call with system time seed failed"
cleanup()
else
usermsg "RandomInt with system time seed returned %u" rNum
endif
;generate a random number with the our seed
dllcall hdll "RandomInt" seed rNum
if (failure)
usermsg "RandomInt call with our seed failed"
cleanup()
else
usermsg "RandomInt with our seed returned %u" rNum
endif
cleanup()
endproc