c style Win32::API interface

pg has asked for the wisdom of the Perl Monks concerning the following question:

I posted Re: opening the cd rom yesterday, but now I have a question myself. I copied the original code here, so it is easy to reference. It was a piece of code to eject CDROM:

use Win32::API;

use strict;
use warnings;

my $f = Win32::API->new("winmm", "mciSendString", "PPNN", "N");
my $ret = ' ' x 127;  
my $return = $f->Call('set CDAudio door open', $ret, 127, 0);
[download]

I came from c background, so I tried to modify the API interface to c style, which makes much more sense to me:

use Win32::API;

use strict;
use warnings;

my $f = Win32::API->new("winmm", "long mciSendString(char * a, char * 
+b, long c, long d)");
my $ret = ' ' x 127;  
my $return = $f->Call('set CDAudio door open', $ret, 127, 0);
[download]

This didn't work, and core dump. I tried couple of other variances, but none of them worked. Please help.

Update:

Changed the code to something like this:

use Win32::API;

use strict;
use warnings;

my $f = Win32::API->new("winmm", 'long mciSendString(LPSTR a, LPSTR b,
+ long c, long d)');
my $ret = ' ' x 127;
$f->Call('set CDAudio door open', $ret, 127, 0);
[download]

Now it gives this error:

Modification of a read-only value attempted at C:/Perl/site/lib/Win32/
+API/Type.p
m line 195, <DATA> line 164.
[download]

Comment on c style Win32::API interface Select or Download Code

Replies are listed 'Best First'.
Re: c style Win32::API interface by Roger (Parson) on Oct 05, 2004 at 06:10 UTC
There is a bug in the prototype definition. The quickest solution is to patch the Win32::API module by 'voiding' the custom prototype. `... my $f = Win32::API->new("winmm", "long mciSendString(LPSTR a, LPSTR b, + long c, long d)"); delete $f->{proto}; delete $f->{intypes}; ...` [download] This will force Win32::API to behave the same as `Win32::API->new("winmm", "PPNN", "N");` [download] It is often useful to turn on the internal debugging of Win32::API to work out what is the prototype parser doing. Turn on debugging with `$Win32::API::DEBUG = 1;`. This shows that in your first prototype, the char * was interpreted as char. Win32::API was not doing a good job at parsing char *. (grin...)	[reply] [d/l] [select]
Re: c style Win32::API interface by dfaure (Chaplain) on Oct 05, 2004 at 05:53 UTC
You just have a small bug in the prototype you use. The real one is there: `MCIERROR mciSendString( LPCTSTR lpszCommand, LPTSTR lpszReturnString, UINT cchReturn, HANDLE hwndCallback );` [download] ____ HTH, Dominique My two favorites: If the only tool you have is a hammer, you will see every problem as a nail. --Abraham Maslow Bien faire, et le faire savoir...	[reply] [d/l]