C++ headache

Thanks for quite an instuctive question =)

Just in general, if you have to cast something like that explicitly it's almost surely the wrong approach...

If you say:

std::transform(string.begin(), string.end(), string.begin(), &std::ctype<char>::toupper );

then what it tries to do it:

(&std::ctype<char>::toupper)( *on_iterator );

which is certainly wrong.

You have to use binders to make it into a member function functor, then bind the address of the object to get it down to a normal unary functor. mem_fun and bind1st and bind2nd are your friends ( or boost::bind if you prefer nice(r) syntax :P ).

Here's my little test program:

#include <iostream>#include <string>#include <algorithm>#include <locale>#include <boost/bind.hpp>int main() {	std::string s = "tEstING...\n";	const std::ctype<char> &c = std::use_facet< std::ctype<char> >( std::locale() );	typedef char ( std::ctype<char>::* char_ctype_char_const_ptr)(char)const;	char_ctype_char_const_ptr fp = &std::ctype<char>::toupper;	std::transform( s.begin(), s.end(), s.begin(),/* uncomment your functor and syntax of choice *///		toupper );					std::bind1st( std::mem_fun( fp ), &c ) );//		boost::bind( fp, &c, _1 ) );//		boost::bind( fp, boost::ref(c), _1 ) );	std::cout << s << std::endl;	return 0;}

The uncommented line is the method you were hoping to use, in a standards-compliant way. toupper's there for testing, and the boost methods are nicer ways.

Note that you can't copy std::ctype<char> s ( protected destructor ), so you have to use references or pointers in the binding -- neither of the following work:
std::bind1st( std::mem_fun_ref( fp ), c ) );
boost::bind( fp, c, _1 ) );

* me22 closes _The_C++_Programming_Language_ :)

There are two overloads of toupper, one in <cctype>, one in <locale>. To select the one you want (likely the one in <cctype>), cast the pointer thusly (int (*)(int)) &toupper.

std::transform(str.begin(), str.end(), str.begin(), (int (*)(int)) &toupper )

Alternatively, grab boost 1.32, and just use the string-specific algorithms they provide.

it has to be said, that this is one of the areas the standard library falls down, IMO. They've made what should be a simple, relatively common operation overly complex in order to increase genericity (is that a word?).

What would be wrong with a simple std::string::to_upper() method?

Quote:

Original post by ChaosEngine What would be wrong with a simple std::string::to_upper() method?

What locale should it use?

Quote:

Original post by Fruny Quote: Original post by ChaosEngine What would be wrong with a simple std::string::to_upper() method? What locale should it use?

That wouldn't be an issue if everyone would just use Unicode, would it? ::sigh::

This reminds of the tale of a King, an electrical engineer and a software engineer. The king wanted to design a toaster. To make a long story short, the electrical engineer married his daughter and the king beheaded the software engineer.

Quote:

Original post by Fruny Quote: Original post by ChaosEngine What would be wrong with a simple std::string::to_upper() method? What locale should it use?

ok, I'll admit it. I don't really understand locales, (never really had call to use them). But surely a default locale could be speicified in the function arguements?