Concatenando di const_string

Question

Come faccio a concatenare due di const_string? La sua casa http://conststring.sourceforge.net/ dice citazione:

Si usa anche modelli di espressione per la concatenazione, eliminando efficacemente in testa derivante dalla creazione di oggetti temporanei intermedi.

Così ho pensato che la sua forma più semplice

typedef class boost::const_string<char> csc;
csc a, b;
csc c = a+b;

dovrebbe funzionare. Ma gcc-4.6 lamenta operatore +. Perché? Devo getto a e b a std::string?

uscita Errore segue:

semnet/realfile.cpp:185:13: error: no match for ‘operator+’ in ‘a + b’
semnet/realfile.cpp:185:13: note: candidates are:
/usr/include/c++/4.6/bits/stl_bvector.h:352:3: note: std::_Bit_const_iterator std::operator+(std::ptrdiff_t, const std::_Bit_const_iterator&)
/usr/include/c++/4.6/bits/stl_bvector.h:352:3: note:   no known conversion for argument 1 from ‘csc’ to ‘std::ptrdiff_t’
/usr/include/c++/4.6/bits/stl_bvector.h:266:3: note: std::_Bit_iterator std::operator+(std::ptrdiff_t, const std::_Bit_iterator&)
/usr/include/c++/4.6/bits/stl_bvector.h:266:3: note:   no known conversion for argument 1 from ‘csc’ to ‘std::ptrdiff_t’
/usr/include/c++/4.6/bits/basic_string.h:2414:20: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, _CharT)
/usr/include/c++/4.6/bits/basic_string.h:2408:27: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, const _CharT*)
/usr/include/c++/4.6/bits/basic_string.h:2402:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(_CharT, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2396:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const _CharT*, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2384:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2378:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2372:58: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/basic_string.h:2359:79: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, _CharT)
/usr/include/c++/4.6/bits/basic_string.h:2344:26: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
/usr/include/c++/4.6/bits/basic_string.tcc:710:79: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(_CharT, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/basic_string.tcc:695:58: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/basic_string.h:2307:58: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/stl_iterator.h:1113:43: note: template<class _Iterator> std::move_iterator<_Iterator> std::operator+(typename std::move_iterator<_Iterator>::difference_type, const std::move_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:328:46: note: template<class _Iterator> std::reverse_iterator<_Iterator> std::operator+(typename std::reverse_iterator<_Iterator>::difference_type, const std::reverse_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:897:64: note: template<class _Iterator, class _Container> __gnu_cxx::__normal_iterator<_Iterator, _Container> __gnu_cxx::operator+(typename __gnu_cxx::__normal_iterator<_Iterator, _Container>::difference_type, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)
semnet/realfile.cpp:186:63: error: no match for ‘operator+’ in ‘xns + boost::const_string<char>(boost::cref [with T = const char*]((* & chashid_get_name_static(hid))), 4294967295u)’
semnet/realfile.cpp:186:63: note: candidates are:
/usr/include/c++/4.6/bits/stl_bvector.h:352:3: note: std::_Bit_const_iterator std::operator+(std::ptrdiff_t, const std::_Bit_const_iterator&)
/usr/include/c++/4.6/bits/stl_bvector.h:352:3: note:   no known conversion for argument 1 from ‘const csc’ to ‘std::ptrdiff_t’
/usr/include/c++/4.6/bits/stl_bvector.h:266:3: note: std::_Bit_iterator std::operator+(std::ptrdiff_t, const std::_Bit_iterator&)
/usr/include/c++/4.6/bits/stl_bvector.h:266:3: note:   no known conversion for argument 1 from ‘const csc’ to ‘std::ptrdiff_t’
/usr/include/c++/4.6/bits/basic_string.h:2414:20: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, _CharT)
/usr/include/c++/4.6/bits/basic_string.h:2408:27: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, const _CharT*)
/usr/include/c++/4.6/bits/basic_string.h:2402:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(_CharT, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2396:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const _CharT*, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2384:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2378:53: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, std::basic_string<_CharT, _Traits, _Alloc>&&)
/usr/include/c++/4.6/bits/basic_string.h:2372:58: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(std::basic_string<_CharT, _Traits, _Alloc>&&, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/basic_string.h:2359:79: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, _CharT)
/usr/include/c++/4.6/bits/basic_string.h:2344:26: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
/usr/include/c++/4.6/bits/basic_string.tcc:710:79: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(_CharT, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/basic_string.tcc:695:58: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/basic_string.h:2307:58: note: template<class _CharT, class _Traits, class _Alloc> std::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/stl_iterator.h:1113:43: note: template<class _Iterator> std::move_iterator<_Iterator> std::operator+(typename std::move_iterator<_Iterator>::difference_type, const std::move_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:328:46: note: template<class _Iterator> std::reverse_iterator<_Iterator> std::operator+(typename std::reverse_iterator<_Iterator>::difference_type, const std::reverse_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:897:64: note: template<class _Iterator, class _Container> __gnu_cxx::__normal_iterator<_Iterator, _Container> __gnu_cxx::operator+(typename __gnu_cxx::__normal_iterator<_Iterator, _Container>::difference_type, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)
semnet/realfile.cpp:187:1: warning: control reaches end of non-void function [-Wreturn-type]
make: *** [semnet/realfile.o] Fel 1

Compilation exited abnormally with code 2 at Fri Apr 29 15:42:00

Answer 1

Hai include l'intestazione rilevanti, boost/const_string/concatenation.hpp?

Answer 2

La classe const_string contiene un costruttore per concatenazioni:

template<class T, class U>
const_string(concatenation<const_string, T, U> const& expr) // throw(std::bad_alloc, std::length_error)
    : storage_type(0, expr.size())
{
    expr.copy_result_to(const_cast<char_type*>(this->begin()));
}

e la biblioteca in sé contiene una classe concatenation che prende due const_strings.

Si potrebbe utilizzare quelli.

L'intestazione in cui è definita la classe concatenation è anche dove operator+ è definito, btw.