Using external functions

External functions are functions that are written in languages
other than PowerScript and stored in dynamic libraries. External functions are stored in
dynamic link libraries (DLLs).

You can use external functions written in any language that
supports the standard calling sequence for 32-bit platforms.

If you are calling functions in libraries that you have written
yourself, remember that you need to export the functions. Depending
on your compiler, you can do this in the function prototype or in
a linker definition (DEF) file.

Use _stdcall convention

C and C++ compilers typically support several
calling conventions, including _cdecl (the
default calling convention for C programs), _stdcall (the
standard convention for Windows API calls), _fastcall,
and thiscall. PowerBuilder, like many other Windows
development tools, requires external functions to be exported using
the WINAPI (_stdcall) format. Attempting
to use a different calling convention can cause an application crash.

When you create your own C or C++ DLLs containing
functions to be used in PowerBuilder, make sure that they use the
standard convention for Windows API calls. For example, if you are
using a DEF file to export function definitions, you can declare
the function like this:

Using PBNI You can also call external functions in PowerBuilder extensions.
PowerBuilder extensions are built using the PowerBuilder Native
Interface (PBNI). For more information about building PowerBuilder
extensions, see the PowerBuilder Native Interface Programmer’s
Guide and Reference
. For more information about using
PowerBuilder extensions, see the PowerBuilder Extension Reference
.

Declaring external functions

Before you can use an external function in a script, you must
declare it.

Two types

You can declare two types of external functions:

• Global external
  functions, which are available anywhere in the application
• Local external functions,
  which are defined for a particular type of window, menu, user object,
  or user-defined function
  These functions are part of the object’s definition
  and can always be used in scripts for the object itself. You can
  also choose to make these functions accessible to other scripts
  as well.

Datatypes for external function arguments

When you declare an external function, the datatypes of the
arguments must correspond with the datatypes as declared in the
function’s source definition.

For a comparison of datatypes in external
functions and datatypes in PowerBuilder, see the section on declaring
and calling external functions in the PowerScript Reference
.

To declare an external function:

1. If you are declaring a local external function,
   open the object for which you want to declare it.

2. In the Script view, select Declare in the first
   drop-down list and either Global External Functions or Local External
   Functions from the second list.

3. Enter the function declaration in the Script view.

   For the syntax to use, see the PowerScript
   Reference
   or the examples below.

4. Save the object.

   PowerBuilder compiles the declaration. If there are syntax errors,
   an error window opens, and you must correct the errors before PowerBuilder can save
   the declaration.

Modifying existing functions You can also modify existing external function declarations
in the Script view.

Sample declarations

Suppose you have created a C dynamic library, SIMPLE.DLL,
that contains a function called SimpleFunc that
accepts two parameters: a character string and a structure. The
following statement declares the function in PowerBuilder, passing
the arguments by reference:

By default, PowerBuilder handles string arguments and return
values as if they have Unicode encoding. If SimpleFunc passes ANSI
strings as arguments, you must use this syntax to declare it:

Declaring Windows API functions

The Windows API includes over a thousand functions that you
can call from PowerBuilder. The following examples show sample declarations
for functions in the 32-bit Windows API libraries KERNEL32.DLL, GDI32.DLL, and USER32.DLL.

Windows API calls Some 32-bit function names end with A (for ANSI) or W (for
wide). Use wide function names in PowerBuilder.

For a complete list of Windows API functions,
see the Microsoft Windows SDK documentation. For examples of PowerBuilder declaration
syntax and scripts, search for Windows API calls in the Technical Documents section of the Sybase Web site
.

The following statements declare a function that gets the
handle of any window that is called by name, and a function that
releases the open object handle:

The following statement declares a function that draws a pie
chart based on the coordinates received:

The following statement declares an external C function named IsZoomed:

A script that uses IsZoomed is included
as an example in “Using utility functions
to manage information”.

For more information about these functions,
see the Microsoft documentation in the MSDN Library
.

Passing arguments

In PowerBuilder, you can define external functions that expect arguments
to be passed by reference or by value. When you pass an argument
by reference, the external function receives a pointer to the argument
and can change the contents of the argument and return the changed
contents to PowerBuilder. When you pass the argument by value, the
external function receives a copy of the argument and can change
the contents of the copy of the argument. The changes affect only
the local copy; the contents of the original argument are unchanged.

The syntax for an argument that is passed by reference is:

The syntax for an argument that is passed by value is:

Passing numeric datatypes

The following statement declares the external function TEMP in PowerBuilder. This
function returns an integer and expects an integer argument to be
passed by reference:

The same statement in C would be:

Since the argument is passed by reference, the function can
change the contents of the argument, and changes made to the argument
within the function will directly affect the value of the original
variable in PowerBuilder. For example, the C statement *degree = 75 would
change the argument named degree to 75 and return 75 to PowerBuilder.

The following statement declares the external function TEMP2 in PowerBuilder.
This function returns an Integer and expects
an Integer argument to be passed by value:

The same statement in C would be:

Since the argument is passed by value, the function can change
the contents of the argument. All changes are made to the local
copy of the argument; the variable in PowerBuilder is not affected.

Passing strings

PowerBuilder assumes all string arguments and returned values
use Unicode encoding. If a function uses strings with ANSI encoding,
you need to add an ALIAS FOR clause to the function declaration
and add a semicolon followed by the ansi keyword.
For example:

Passing by value The following statement declares the external C function NAME in PowerBuilder.
This function expects a String argument with
Unicode encoding to be passed by value:

The same statement in C would point to a buffer containing
the String:

Since the String is passed by value,
the C function can change the contents of its local copy of CODE,
but the original variable in PowerBuilder is not affected.

Passing by reference PowerBuilder has access only to its own memory. Therefore, an
external function cannot return to PowerBuilder a pointer to a string.
(It cannot return a memory address.)

When you pass a string to an external function, either by
value or by reference, PowerBuilder passes a pointer to the string.
If you pass by value, any changes the function makes to the string
are not accessible to PowerBuilder. If you pass by reference, they
are.

The following statement declares the external C function NAME2 in PowerBuilder.
This function returns a String and expects
a String argument to be passed by reference:

In C, the statement would be the same as when the argument
is passed by value, shown above:

The String argument is passed by reference,
and the C function can change the contents of the argument and the
original variable in PowerBuilder. For example, Strcpy(CODE,STUMP) would
change the contents of CODE to STUMP and
change the variable in the calling PowerBuilder script to the contents
of variable STUMP.

If the function NAME2 in the preceding
example takes a user ID and replaces it with the user’s
name, the PowerScript string variable CODE must
be long enough to hold the returned value. To ensure that this is
true, declare the String and then use the Space function
to fill the String with blanks equal to the maximum
number of characters you expect the function to return.

If the maximum number of characters allowed for a user’s
name is 40 and the ID is always five characters, you would fill
the String CODE with 35
blanks before calling the external function:

For information about the Space function,
see the PowerScript Reference
.

Passing chars to C functions Char variables passed to external C functions are
converted to the C char type before passing.
Arrays of Char variables are converted to the
equivalent C array of char variables.

An array of Char variables embedded in
a structure produces an embedded array in the C structure. This
is different from an embedded String, which results
in an embedded pointer to a string in the C
structure.

Recommendation Whenever possible, pass String variables
back to PowerBuilder as a return value from the function.

Calling external functions on UNIX

In PowerBuilder custom class user objects that you plan to
deploy as EAServer components
on a UNIX platform, you can call external functions in shared libraries
compiled on the operating system where the server is running. You cannot
call external functions in libraries that make Windows API calls
or rely on graphical processing.

You use the standard PowerScript syntax to declare functions
that reside in UNIX shared libraries. For example, this statement
declares the function getcwd in the standard
C library on Solaris:

You call the function from a script in your application in
the way you call any other function. In this example, the space function
allocates enough space to hold the directory name returned by getcwd:

Updating the load library path On UNIX, when your component calls an external function, it
must be able to find the shared library in which that function resides.
To ensure this, you must update the library path environment variable
to include the directory where that shared library is stored.

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