From: Kim Minh Kaplan <kimminh.kaplan+nomuch@afnic.fr>
To: Vladimir Marek <vlmarek@volny.cz>
Subject: Re: [PATCH] don't store temporary value returned from c_str()
References: <1366405933-17223-1-git-send-email-Vladimir.Marek@oracle.com>
	<m2sj2cjp2b.fsf@guru.guru-group.fi>
	<20130427101134.GI10394@pub.cz.oracle.com>
	<8761z4h7ih.fsf@kaki.tech.prive.nic.fr>
	<20130430084852.GA19599@pub.cz.oracle.com>
Date: Tue, 30 Apr 2013 09:44:01 +0000
In-Reply-To: <20130430084852.GA19599@pub.cz.oracle.com> (Vladimir Marek's
	message of "Tue, 30 Apr 2013 10:48:52 +0200")
Message-ID: <87ehdsfj4u.fsf@kaki.tech.prive.nic.fr>
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Cc: Tomi Ollila <tomi.ollila@iki.fi>, notmuch@notmuchmail.org
Precedence: list

Vladimir Marek=C2=A0:

> Thank you, I found it eventually too. But I wrote little test program
> (attached) which confused me. I haven't had much time to take a look
> into it since weekend.
>
> The idea is to have temporary object where I can detect whether
> destructor was called.
>
> I thought that
>
> printf ("%s\n", s.c_str());
> will print "test"
>
> and
>
> x=3Ds.c_str();
> printf ("%s\n", x);
>
> will print "destroyed"
>
> On my machine both prints "destroyed".

You have to somehow instantiate a temporary object, using a function
call for example.

    #include <string.h>
    #include <stdio.h>
    struct example {
      char data[10];
      char *c_str() { return data; }
     example() { strcpy(data, "test"); }
      ~example() { strcpy(data, "destroyed"); }
    };
    example foo()
    {
      example res;
      return res;
    }
    main()
    {
      printf("%s\n", foo().c_str());
      char *x =3D foo().c_str();
      printf("%s\n", x);
    }

Kim Minh.