• NAME
• SUPPORTED PLATFORMS
• SYNOPSIS
• ABSTRACT
• CREDITS
• INSTALLATION
• DESCRIPTION
• IMPORTING A FUNCTION
• CALLING AN IMPORTED FUNCTION
• AUTHOR

NAME

Win32::API - Implementation of arbitrary Win32 APIs.

SUPPORTED PLATFORMS

• Windows

SYNOPSIS

  use Win32::API;
  $function = new Win32::API($library, 
                             $functionname, 
                             \@argumenttypes, 
                             $returntype);
  $return = $function->Call(@arguments);

ABSTRACT

With this module you can import and call arbitrary functions from Win32's Dynamic Link Libraries (DLL).

The current version of Win32::API is available at:

  http://www.divinf.it/dada/perl/api/

It is also available on your nearest CPAN mirror (but allow a few days for worldwide spreading of the latest version) reachable at:

  http://www.perl.com/CPAN/authors/Aldo_Calpini/

CREDITS

All the credits go to Andrea Frosini ( frosini@programmers.net ), for his bits of magic - eg. the assembler trick that make this thing work. A big thank you also to Gurusamy Sarathy ( gsar@engin.umich.edu ) for his help in XS development :)

INSTALLATION

This module comes with pre-built binaries for:

The Perl for Win32 port by ActiveWare: Build 300 or higher (EXCEPT 304!)

The core Perl 5.004 distribution: Built on the Win32 platform, of course...

To install the package, just change to the directory in which you uncompressed it and type the following:

    install

This will take care of copying the right files to the right places for use by all your perl scripts.

If you're running the core Perl 5.004 distribution, you can also build the extension by yourself with the following procedure:

    perl Makefile.PL
    nmake
    nmake install

If you are instead running the ActiveWare Perl for Win32 port, the sources to rebuild the extension are in the ActiveWare/source directory. You should put those files in the following directory:

    (perl-src)\ext\Win32\API

Where (perl-src) is the location of your Perl-Win32 source files.

DESCRIPTION

To use this module put the following line at the beginning of your script:

    use Win32::API;

You can now use the new() function of the Win32::API module to create a new API object (see IMPORTING A FUNCTION) and then invoke the Call() method on this object to perform a call to the imported API (see CALLING AN IMPORTED FUNCTION).

IMPORTING A FUNCTION

You can import a function from a Dynamic Link Library (DLL) file with the new() function. This will create a Perl object that contains the reference to that function, which you can later Call(). You need to pass 4 parameters:

1. The name of the library from which you want to import the function.
   
2. The name of the function (as exported by the library).
   
3. The number and types of the arguments the function expects as input.
   
4. The type of the value returned by the function.
   

To explain better their meaning, let's make an example: I want to import and call the Win32 API GetTempPath(). This function is defined in C as:

    DWORD WINAPI GetTempPathA( DWORD nBufferLength, LPSTR lpBuffer );

This is documented in the Win32 SDK Reference; look for it on the Microsoft's WWW site. If you own Visual C++, searching in the include files is much faster.

1.

The first parameter is the name of the library file that exports this function; our function resides in the KERNEL32.DLL system file. When specifying this name as parameter, the .dll extension is implicit, and if no path is given, the file is searched through the Windows directories. So I don't have to write C:\windows\system\kernel32.dll; only kernel32 is enough:

    $GetTempPath = new Win32::API("kernel32", ...

2.

Now for the second parameter: the name of the function. It must be written exactly as it is exported by the library (case is significant here). If you are using Windows 95 or NT 4.0, you can use the Quick View command on the DLL file to see the function it exports. Note that many Win32 APIs are exported twice, with the addition of a final A or W to their name, for - respectively - the ASCII and the Unicode version. Win32::API, when a function name is not found, will actually append an A to the name and try again. If you are using Unicode, you will just need to rebuild the module; then Win32::API will try with the W. So my function name will be:

    $GetTempPath = new Win32::API("kernel32", "GetTempPath", ...

Note that GetTempPath is really loaded as GetTempPathA.

3.

The third parameter, the input parameter list, specifies how many arguments the function wants, and their types. It MUST be passed as a list reference. The following forms are valid:

    [a, b, c, d]
    \@LIST

But those are not:

    (a, b, c, d)
    @LIST

The number of elements in the list specifies the number of parameters, and each element in the list specifies the type of an argument; allowed types are:

I: value is an integer

N: value is a number (long)

P: value is a pointer (to a string, structure, etc...)

Our function needs two parameters: a number (DWORD) and a pointer to a string (LPSTR):

    $GetTempPath = new Win32::API("kernel32", "GetTempPath", [N, P], ...

4.

The fourth and final parameter is the type of the value returned by the function. It can be one of the types seen above, plus another type named V (that stands for void) to indicate that the function doesn't return a value. In our example the value returned by GetTempPath() is a DWORD, so our return type will be N:

    $GetTempPath = new Win32::API("kernel32", "GetTempPath", [N, P], N);

Now the line is complete, and the API GetTempPath() is available for use in Perl. Before you can call it, you should test that $GetTempPath is defined, otherwise either the function or the library has not been found.

CALLING AN IMPORTED FUNCTION

To effectively make a call to an imported function you must use the Call() method on the Win32::API object you created. To continue with the example from the previous paragraph, I can call the GetTempPath() API via the method:

    $GetTempPath->Call(...

Of course I have to pass the parameters as defined in the import phase. In particular, if the number of parameters does not match (in the example, if I call GetTempPath() with more or less than two parameters), Perl will croak an error message and die.

So I need two parameters here: the first is the length of the buffer that will hold the returned temporary path, the second is the buffer itself. For numerical parameters you can use either a constant expression or a variable, while for pointers you must use a variable name (no reference, just a plain variable name). Also note that memory must be allocated before calling the function. For example, if I want to pass a buffer of 80 characters to GetTempPath(), I have to initialize it before with:

    $lpBuffer = " " x 80;

This allocates a string of 80 characters. If you don't do so, you'll probably get 'Runtime exception' errors, and generally nothing will work. My call should therefore include:

    $lpBuffer = " " x 80;
    $GetTempPath->Call(80, $lpBuffer);

And the result will be stored in the $lpBuffer variable. Note, however, that Perl does not trim the variable, so $lpBuffer will contain 80 characters in return; the exceeding characters will be spaces, since I initialized the variable with " " x 80. In this case I'm lucky enough, because the value returned by the GetTempPath() function is the length of the string, so to get the actual temporary path I write:

    $lpBuffer = " " x 80;
    $return = $GetTempPath->Call(80, $lpBuffer);
    $TempPath = substr($lpBuffer, 0, $return);

If you don't know the length of the string, you can usually cut it at the \0 (ASCII zero) character, which is the string delimiter in C:

    $TempPath = ((split(/\0/, $lpBuffer))[0];

    # or

    $lpBuffer =~ s/\0.*$//;
    $TempPath = $lpBuffer;

Another note: to pass a pointer to a structure in C, you'll have to pack() the required elements in a variable. And of course, to access the values stored in a structure, unpack() it as required. An example of how it works: we have the POINT structure defined in C as:

    typedef struct {
        LONG  x;
        LONG  y;
    } POINT;

Thus, to call a function that uses a POINT structure you will need the following lines:

    $GetCursorPos = new Win32::API("user32", "GetCursorPos", [P], V);

    $lpPoint = pack("LL", 0, 0); # store two LONGs
    $GetCursorPos->Call($lpPoint);
    ($x, $y) = unpack("LL", $lpPoint); # get the actual values

The rest is left as an exercise to the reader...

AUTHOR

Aldo Calpini ( dada@divinf.it ).