wxWidgets/include/wx/anystr.h

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///////////////////////////////////////////////////////////////////////////////
// Name: wx/anystr.h
// Purpose: wxAnyStrPtr class declaration
// Author: Vadim Zeitlin
// Created: 2009-03-23
// RCS-ID: $Id$
// Copyright: (c) 2008 Vadim Zeitlin <vadim@wxwidgets.org>
// Licence: wxWindows licence
///////////////////////////////////////////////////////////////////////////////
#ifndef _WX_ANYSTR_H_
#define _WX_ANYSTR_H_
#include "wx/string.h"
// ----------------------------------------------------------------------------
// wxAnyStrPtr
//
// Notice that this is an internal and intentionally not documented class. It
// is only used by wxWidgets itself to ensure compatibility with previous
// versions and shouldn't be used by user code. When you see a function
// returning it you should just know that you can treat it as a string pointer.
// ----------------------------------------------------------------------------
// This is a helper class convertible to either narrow or wide string pointer.
// It is similar to wxCStrData but, unlike it, can be NULL which is required to
// represent the return value of wxDateTime::ParseXXX() methods for example.
//
// NB: this class is fully inline and so doesn't need to be DLL-exported
class wxAnyStrPtr
{
public:
// ctors: this class must be created from the associated string or using
// its default ctor for an invalid NULL-like object; notice that it is
// immutable after creation.
// ctor for invalid pointer
wxAnyStrPtr()
: m_str(NULL)
{
}
// ctor for valid pointer into the given string (whose lifetime must be
// greater than ours and which should remain constant while we're used)
wxAnyStrPtr(const wxString& str, const wxString::const_iterator& iter)
: m_str(&str),
m_iter(iter)
{
}
// default copy ctor is ok and so is default dtor, in particular we do not
// free the string
// various operators meant to make this class look like a superposition of
// char* and wchar_t*
// this one is needed to allow boolean expressions involving these objects,
// e.g. "if ( FuncReturningAnyStrPtr() && ... )" (unfortunately using
// unspecified_bool_type here wouldn't help with ambiguity between all the
// different conversions to pointers)
operator bool() const { return m_str != NULL; }
// at least VC6 and VC7 also need this one or they complain about ambiguity
// for !anystr expressions
bool operator!() const { return !((bool)*this); }
// and these are the conversions operator which allow to assign the result
// of FuncReturningAnyStrPtr() to either char* or wxChar* (i.e. wchar_t*)
operator const char *() const
{
if ( !m_str )
return NULL;
// check if the string is convertible to char at all
//
// notice that this pointer points into wxString internal buffer
// containing its char* representation and so it can be kept for as
// long as wxString is not modified -- which is long enough for our
// needs
const char *p = m_str->c_str().AsChar();
if ( *p )
{
// find the offset of the character corresponding to this iterator
// position in bytes: we don't have any direct way to do it so we
// need to redo the conversion again for the part of the string
// before the iterator to find its length in bytes in current
// locale
//
// NB: conversion won't fail as it succeeded for the entire string
p += strlen(wxString(m_str->begin(), m_iter).mb_str());
}
//else: conversion failed, return "" as we can't do anything else
return p;
}
operator const wchar_t *() const
{
if ( !m_str )
return NULL;
// no complications with wide strings (as long as we discount
// surrogates as we do for now)
//
// just remember that this works as long as wxString keeps an internal
// buffer with its wide wide char representation, just as with AsChar()
// above
return m_str->c_str().AsWChar() + (m_iter - m_str->begin());
}
// Because the objects of this class are only used as return type for
// functions which can return NULL we can skip providing dereferencing
// operators: the code using this class must test it for NULL first and if
// it does anything else with it it has to assign it to either char* or
// wchar_t* itself, before dereferencing.
//
// IOW this
//
// if ( *FuncReturningAnyStrPtr() )
//
// is invalid because it could crash. And this
//
// const char *p = FuncReturningAnyStrPtr();
// if ( p && *p )
//
// already works fine.
private:
// the original string and the position in it we correspond to, if the
// string is NULL this object is NULL pointer-like
const wxString * const m_str;
const wxString::const_iterator m_iter;
wxDECLARE_NO_ASSIGN_CLASS(wxAnyStrPtr);
};
#endif // _WX_ANYSTR_H_