wxString, Format etc.

[Matthias Buelow]

Hi folks,

what's the rationale behind wxString wrt. to converting to/from char *
etc.? Is there any at all? Why doesn't wxString::Format understand
wxStrings?

One of the things I want to do is use wxString::Format with wxStrings.
Seems this hasn't been anticipated. Now I've tried the various
conversion functions (c_str(), char_str(), fn_str(), mb_str(),
wchar_str(), wc_str(), To8BitData()) and only c_str() seems to work,
however, the documentation says that it'll no longer work with wxWidgets 3.
What am I supposed to use then? Another thing is pathnames; I'm using
char_str() since fn_str() (which, according to the documentation, is the
proper thing to use, doesn't work.)
What's the canonical way to get anything useful out of a wxString?
Portably and without having to write special code for each combination
of OS/char width?

I'm currently using wxGTK 2.8.7 / Unicode but it should work on all
platforms (I don't care for ANSI builds).
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[Vadim Zeitlin-4]

On Mon, 08 Sep 2008 18:14:00 +0200 Matthias Buelow <mkb@...> wrote:

MB> what's the rationale behind wxString wrt. to converting to/from char *
MB> etc.?

 What is the question here? I.e. rationale for what exactly are you asking
about?

MB> Why doesn't wxString::Format understand wxStrings?

 Because objects can't be passed to vararg functions. This is undefined
behaviour in C++.

 You may be interested to know that in wx3 Format() (and Printf() and many
other functions which used to be vararg) are now (pseudo-)variadic
templates and so do accept strings being passed directly to them.

MB> One of the things I want to do is use wxString::Format with wxStrings.
MB> Seems this hasn't been anticipated.

 I do wonder how did we live for 15 years without it...

MB> Now I've tried the various
MB> conversion functions (c_str(), char_str(), fn_str(), mb_str(),
MB> wchar_str(), wc_str(), To8BitData()) and only c_str() seems to work,
MB> however, the documentation says that it'll no longer work with wxWidgets 3.

 Where exactly did you read it? If the documentation says this it should be
corrected because this is patently wrong. As I wrote above, c_str() won't
be _necessary_ in wx3 in this case but it doesn't mean it's not going to
work.

MB> What's the canonical way to get anything useful out of a wxString?

 This depends on what you consider to be useful. If "useful" means
"suitable to be passed to wxString::Format("%s")" then the answer is
c_str().

MB> I'm currently using wxGTK 2.8.7 / Unicode but it should work on all
MB> platforms (I don't care for ANSI builds).

 Then c_str() is the same as wc_str() in your case so it's impossible that
wc_str() doesn't work if c_str() does.

 Regards,
VZ

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[Matthias Buelow]

Vadim Zeitlin wrote:

> MB> Why doesn't wxString::Format understand wxStrings?
>
>  Because objects can't be passed to vararg functions. This is undefined
> behaviour in C++.

Where's the problem with expecting a reference or a pointer? The thing
is, I want to pass a wxString (however) to a wxString utility member
function and not have to guess which of the *_str() functions would be
necessary in this case. This is a completely uninteresting detail at
that point that I don't want to be bothered with. Why make an own string
class if it can't be used ubiquitously in the library which defines it?

> only c_str() seems to work,
> MB> however, the documentation says that it'll no longer work with wxWidgets 3.
>
>  Where exactly did you read it? If the documentation says this it should be
> corrected because this is patently wrong. As I wrote above, c_str() won't
> be _necessary_ in wx3 in this case but it doesn't mean it's not going to
> work.

http://docs.wxwidgets.org/stable/wx_wxstring.html#wxstringcstr

> MB> What's the canonical way to get anything useful out of a wxString?
>
>  This depends on what you consider to be useful. If "useful" means
> "suitable to be passed to wxString::Format("%s")" then the answer is
> c_str().

Useful would mean that all functions in WxWidgets that want some kind of
string should accept a wxString, and not demand various forms of (w)char
*, (w)char buffers, or whatever, plus a consistent and reliable way of
converting/extracting to/from char* for system functions (it doesn't
matter if the text is actually utf-8 or ASCII, or any other encoding,
since filesystem functions are usually ignorant of encodings, or use a
default one (utf-8, on Windoze) which should be used then.)
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[Vadim Zeitlin-4]

On Tue, 09 Sep 2008 15:17:40 +0200 Matthias Buelow <mkb@...> wrote:

MB> Vadim Zeitlin wrote:
MB>
MB> > MB> Why doesn't wxString::Format understand wxStrings?
MB> >
MB> >  Because objects can't be passed to vararg functions. This is undefined
MB> > behaviour in C++.
MB>
MB> Where's the problem with expecting a reference or a pointer?

 Passing pointer to printf() prints out a pointer, not the object. Passing
a reference is undefined behaviour and doesn't work.

MB> The thing is, I want to pass a wxString (however) to a wxString utility
MB> member function and not have to guess which of the *_str() functions
MB> would be necessary in this case.

 You don't need to guess. "%s" format specifier expects "wxChar *" string,
c_str() returns it. And if you don't know what does c_str() return, you
really should.

MB> >  Where exactly did you read it? If the documentation says this it should be
MB> > corrected because this is patently wrong. As I wrote above, c_str() won't
MB> > be necessary in wx3 in this case but it doesn't mean it's not going to
MB> > work.
MB>
MB> http://docs.wxwidgets.org/stable/wx_wxstring.html#wxstringcstr

 Please reread this carefully. It doesn't nearly say what you wrote.

MB> > MB> What's the canonical way to get anything useful out of a wxString?
MB> >
MB> >  This depends on what you consider to be useful. If "useful" means
MB> > "suitable to be passed to wxString::Format("%s")" then the answer is
MB> > c_str().
MB>
MB> Useful would mean that all functions in WxWidgets that want some kind of
MB> string should accept a wxString, and not demand various forms of (w)char
MB> *, (w)char buffers, or whatever,

 There is no whatever. All non-vararg functions do accept wxStrings (and in
wx3 vararg ones accept them too), for vararg functions you need to use
c_str().

MB> plus a consistent and reliable way of converting/extracting to/from
MB> char* for system functions

 There is no such thing as "system functions" unfortunately. Different
functions happen to require different encodings, hence the existence of
several wxConvXXX classes.

 Regards,
VZ

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[Paul Koning-4]

>>>>> "Matthias" == Matthias Buelow <mkb@...> writes:

 Matthias> Vadim Zeitlin wrote:

 MB> Why doesn't wxString::Format understand wxStrings?
 >>  Because objects can't be passed to vararg functions. This is
 >> undefined behaviour in C++.

 Matthias> Where's the problem with expecting a reference or a
 Matthias> pointer? The thing is, I want to pass a wxString (however)
 Matthias> to a wxString utility member function and not have to guess
 Matthias> which of the *_str() functions would be necessary in this
 Matthias> case. This is a completely uninteresting detail at that
 Matthias> point that I don't want to be bothered with. Why make an
 Matthias> own string class if it can't be used ubiquitously in the
 Matthias> library which defines it?

Because it's a design defect in C++.  Nothing wxWidgets can do about
it.

    paul

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