in reply to Re^4: XS/Inline::C concat *any* two SVs.
in thread XS/Inline::C concat *any* two SVs.

You can't concatenate onto a readonly scalar, in either Perl or XS. 
#!/usr/bin/perl
use strict;
use warnings;

use Inline C => <<'END_C';

void 
readonly(SV *sv) {
    SvREADONLY_on(sv);
}

END_C

my $foo = "foo";
readonly($foo);

# This dies with: 
# "Modification of a read-only value attempted at cat_readonly.plx lin
+e 16."
$foo .= "bar";

# unreachable:
print "$foo\n";

[download]

So, if you have to deal with the possibility that your first scalar might be readonly, you have to do $a = $a . $b or its equivalent in XS rather than $a .= $b. It might be wasteful, but it's the only way.

--
Marvin Humphrey
Rectangular Research ― http://www.rectangular.com

Replies are listed 'Best First'.
Re^6: XS/Inline::C concat *any* two SVs.
by BrowserUk (Patriarch) on May 28, 2006 at 15:20 UTC

    If you look at the OP, you'll see that is exactly what I do.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
Re^6: XS/Inline::C concat *any* two SVs.
by BrowserUk (Patriarch) on May 28, 2006 at 15:22 UTC

    If you look at the OP, you'll see that is exactly what I do. But only for readonly scalars.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]

      Your original post is pretty messed up, so please forgive me if I used your more recent explanation, however imprecise, as a reference instead. I'm trying to help, here.

      --
      Marvin Humphrey
      Rectangular Research ― http://www.rectangular.com
[reply]
        Your original post is pretty messed up,

        In what way? 1 short paragraph, 2 questions, 10 lines of code, 5 tests and the (correct) output from those tests.

        As you'll see, your help is much appreciated, but I wonder how you can say the original post is "messed up"?

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

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