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Re: this cast to const char*

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On 2011-05-06 09:59:31 -0400, Goran said:

> On May 5, 7:27 pm, "Gernot Frisch" <m...@privacy.net> wrote:
>> Hi,
>> 
>> with "MFC" I can do:
>> CString str(_T("test"); printf("%s", str); // prints "test"
>> 
>> With my own string class, however, there seems to be a 4 byte "header"
>> before the string data.
>> 
>> I have the member >const TCHAR* m_data;< as the first member of my string
>> class.
>> 
>> How does MS doe this?
> 
> Luck (well, cheating). First of all, as said, passing non-pod is UB.
> What actually happens is that your string is passed to printf as a
> POD. But CString class is made in such a way that "this" is also a
> pointer to the first character (there's more to CString than a
> pointer, and you don't want to know that ;-).
> 
> So... Your code has an error,

No, it doesn't. "Undefined behavior" means only that the C++ standard 
doesn't tell you what the code does. There's nothing preventing a 
compiler from defining the behavior, and there's nothing inherently 
wrong with relying on implementation-specific behavior.

-- 
  Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The 
Standard C++ Library Extensions: a Tutorial and Reference 
(www.petebecker.com/tr1book)

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this cast to const char* "Gernot Frisch" <me@privacy.net> - 2011-05-05 19:27 +0200
  Re: this cast to const char* Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-05-05 19:39 +0200
    Re: this cast to const char* "Balog Pal" <pasa@lib.hu> - 2011-05-06 01:11 +0200
      Re: this cast to const char* Marcel Müller <news.5.maazl@spamgourmet.org> - 2011-05-06 01:54 +0200
        Re: this cast to const char* m0shbear <andrey.vul@gmail.com> - 2011-05-05 17:59 -0700
          Re: this cast to const char* James Kanze <james.kanze@gmail.com> - 2011-05-08 07:08 -0700
            Re: this cast to const char* m0shbear <andrey.vul@gmail.com> - 2011-05-08 17:03 -0700
        Re: this cast to const char* "Balog Pal" <pasa@lib.hu> - 2011-05-06 20:15 +0200
        Re: this cast to const char* James Kanze <james.kanze@gmail.com> - 2011-05-08 07:05 -0700
    Re: this cast to const char* James Kanze <james.kanze@gmail.com> - 2011-05-08 07:02 -0700
  Re: this cast to const char* Felix Bytow <felix.bytow@informatik.tu-chemnitz.de> - 2011-05-05 19:40 +0200
    Re: this cast to const char* Öö Tiib <ootiib@hot.ee> - 2011-05-05 10:52 -0700
  Re: this cast to const char* Öö Tiib <ootiib@hot.ee> - 2011-05-05 10:44 -0700
  Re: this cast to const char* gwowen <gwowen@gmail.com> - 2011-05-05 10:50 -0700
    Re: this cast to const char* Öö Tiib <ootiib@hot.ee> - 2011-05-05 10:58 -0700
      Re: this cast to const char* "Bo Persson" <bop@gmb.dk> - 2011-05-05 20:21 +0200
      Re: this cast to const char* gwowen <gwowen@gmail.com> - 2011-05-05 11:27 -0700
        Re: this cast to const char* Öö Tiib <ootiib@hot.ee> - 2011-05-05 11:37 -0700
          Re: this cast to const char* gwowen <gwowen@gmail.com> - 2011-05-05 22:28 -0700
            Re: this cast to const char* Öö Tiib <ootiib@hot.ee> - 2011-05-06 03:55 -0700
              Re: this cast to const char* "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-05-06 13:25 +0200
                Re: this cast to const char* Öö Tiib <ootiib@hot.ee> - 2011-05-06 06:22 -0700
  Re: this cast to const char* Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-05 22:47 -0700
  Re: this cast to const char* Goran <goran.pusic@gmail.com> - 2011-05-06 06:59 -0700
    Re: this cast to const char* Pete Becker <pete@versatilecoding.com> - 2011-05-06 10:17 -0400
      Re: this cast to const char* James Kanze <james.kanze@gmail.com> - 2011-05-08 07:13 -0700
    Re: this cast to const char* "Gernot Frisch" <me@privacy.net> - 2011-05-09 10:38 +0200
      Re: this cast to const char* Leigh Johnston <leigh@i42.co.uk> - 2011-05-09 13:03 +0100
        Re: this cast to const char* Leigh Johnston <leigh@i42.co.uk> - 2011-05-09 17:51 +0100
      Re: this cast to const char* Öö Tiib <ootiib@hot.ee> - 2011-05-09 09:40 -0700

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