Native calling interface: how to translate "wchar_t"?

Question

I would like to use the ncurses int addwstr(const wchar_t *wstr); function in Perl6.

How could I get a Perl 6 signatures which conveys const wchar_t *wstr of addwstr?

use v6;
use NativeCall;

constant LIB = 'libncursesw.so.5';

sub addwstr(  ?  ) returns int32 is native(LIB) is export {*};

Answer 1

wchar_t is 32 bits on my machine. From the NativeCall doco, you can declare an array of them and the array name will act as the pointer;

#!/usr/bin/env perl6
use v6;
use NCurses;                   # To get iniscr(), endwin() etc
use NativeCall;

# Need to run setlocale from the C library
my int32 constant LC_ALL = 6;           # From locale.h
my sub setlocale(int32, Str) returns Str is native(Str) { * }

constant LIB = 'libncursesw.so.5';
sub addwstr(CArray[int32]) returns int32 is native(LIB) { * }

# The smiley        : Codepoint 0x263a
# Latin space       : Codepoint 0x20  (Ascii decimal ord 32)
# Check mark (tick) : Codepoint 0x2713

my CArray[int32] $wchar_str .= new(0x263a, 0x20, 0x2713);

setlocale(LC_ALL, "");
initscr();
move(2,2);
addwstr( $wchar_str );
nc_refresh;
while getch() < 0 {};
endwin;

This prints "☺ ✓" on my machine. It doesn't work without the call to setlocale.

As an aside, you don't have to use the 'w' functions - you can just pass normal perl6 strings (presumably encoded UTF-8) and it just works. This produces the same result;

#!/usr/bin/env perl6
use v6;
use NCurses;
use NativeCall;

# Need to run setlocale from the standard C library
my int32 constant LC_ALL = 6;           # From locale.h
my sub setlocale(int32, Str) returns Str is native(Str) { * }

my $ordinary_scalar = "☺ ✓";

setlocale(LC_ALL, "");
initscr();
move(2,2);
addstr( $ordinary_scalar );   # No 'w' necessary
nc_refresh;
while getch() < 0 {};
endwin;