From: Vladimir Marek <Vladimir.Marek@Oracle.COM>
To: Kim Minh Kaplan <kimminh.kaplan+nomuch@afnic.fr>
Cc: Tomi Ollila <tomi.ollila@iki.fi>,
notmuch@notmuchmail.org, Vladimir Marek <vlmarek@volny.cz>
Subject: Re: [PATCH] don't store temporary value returned from c_str()
Date: Tue, 30 Apr 2013 10:48:52 +0200 [thread overview]
Message-ID: <20130430084852.GA19599@pub.cz.oracle.com> (raw)
In-Reply-To: <8761z4h7ih.fsf@kaki.tech.prive.nic.fr>
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Hi,
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=s.c_str();
printf ("%s\n", x);
will print "destroyed"
On my machine both prints "destroyed".
I still believe my fix is correct, but I'm not at the position to be
able to defend it at the moment :)
Thank you
--
Vlad
> The january 2012 working draft:
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf
>
> 12.2 Temporary objects [class.temporary]
>
> 1 Temporaries of class type are created in various contexts: binding a
> reference to a prvalue (8.5.3), returning a prvalue (6.6.3) […]
>
> 3 When an implementation introduces a temporary object of a class that
> has a non-trivial constructor (12.1, 12.8), it shall ensure that a
> constructor is called for the temporary object. Similarly, the
> destructor shall be called for a temporary with a non-trivial destructor
> (12.4). Temporary objects are destroyed as the last step in evaluating
> the full-expression (1.9) that (lexically) contains the point where they
> were created.
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#include <stdio.h>
#include <vector>
#include <string.h>
using namespace std;
class array {
vector<char> impl;
public:
array(int size):impl(size) { }
array(array &in):impl(in.impl) { }
char*
operator[](size_t i) {
return &impl[i];
};
~array() {
strcpy(&impl[0], "destroyed");
}
};
class str {
array tmp;
public:
str(const char *input):tmp(100) {
strcpy(tmp[0], input);
};
const char* c_str() {
return (array(tmp))[0];
};
};
int
main (int argc, char **argv)
{
str s("test");
const char *x;
printf ("%s\n", s.c_str());
x=s.c_str();
printf ("%s\n", x);
return 0;
}
next prev parent reply other threads:[~2013-04-30 8:51 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-19 21:12 [PATCH] don't store temporary value returned from c_str() Vladimir.Marek
2013-04-27 9:33 ` Tomi Ollila
2013-04-27 10:11 ` Vladimir Marek
2013-04-27 11:53 ` David Bremner
2013-04-27 15:59 ` Vladimir Marek
2013-04-30 6:12 ` Kim Minh Kaplan
2013-04-30 8:48 ` Vladimir Marek [this message]
2013-04-30 9:44 ` Kim Minh Kaplan
2013-05-01 11:28 ` Vladimir Marek
2013-04-27 12:30 ` Jani Nikula
2013-04-27 13:22 ` Tomi Ollila
2013-04-27 16:05 ` Vladimir Marek
2013-04-29 21:23 ` David Bremner
2013-05-01 21:33 ` Vladimir Marek
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