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| author | Stas Bekman <stas@stason.org> | 2004-05-27 04:25:08 -0700 |
|---|---|---|
| committer | Rafael Garcia-Suarez <rgarciasuarez@gmail.com> | 2004-05-28 06:29:28 +0000 |
| commit | 9adebda4fef8cbc5965f9327c10fca15b814f305 (patch) | |
| tree | 5890001db3450e8b95ce0d8e37fbe0215d978f8e /pod/perlguts.pod | |
| parent | 0b8342839983807250e9f986d89f01500807f071 (diff) | |
| download | perl-9adebda4fef8cbc5965f9327c10fca15b814f305.tar.gz | |
Re: undef loses it magicness when assigned to a variable?
Message-ID: <40B63284.5040203@stason.org>
p4raw-id: //depot/perl@22853
Diffstat (limited to 'pod/perlguts.pod')
| -rw-r--r-- | pod/perlguts.pod | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/pod/perlguts.pod b/pod/perlguts.pod index 9932b37547..99c79d0a43 100644 --- a/pod/perlguts.pod +++ b/pod/perlguts.pod @@ -201,9 +201,22 @@ you can call: SvOK(SV*) The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>. -Its address can be used whenever an C<SV*> is needed. -However, you have to be careful when using C<&PL_sv_undef> as a value in AVs -or HVs (see L<AVs, HVs and undefined values>). + +Its address can be used whenever an C<SV*> is needed. Make sure that +you don't try to compare a random sv with C<&PL_sv_undef>. For example +when interfacing Perl code, it'll work correctly for: + + foo(undef); + +But won't work when called as: + + $x = undef; + foo($x); + +So to repeat always use SvOK() to check whether an sv is defined. + +Also you have to be careful when using C<&PL_sv_undef> as a value in +AVs or HVs (see L<AVs, HVs and undefined values>). There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain boolean TRUE and FALSE values, respectively. Like C<PL_sv_undef>, their |