TITLE: toupper for strings of arbitrary character types

(Source: comp.lang.c++, 18 Oct 2000)


SEBASTIAN: Josh Sebastian (tar_curien@my-deja.com)

:>: int main()
:>:    {
:>:    std::string s = "Hello, world!";
:>:    std::transform(s.begin(), s.end(), s.begin(), std::toupper);


RODRIGUEZ: Fernando Rodríguez (spamers@must.die)

:>The above line should read
:>
:>     std::transform(s.begin(), s.end(), s.begin(),
:>                    static_cast<int(*)(int)>(std::toupper));


UNKNOWN:

:      Would this same technique work on unicode strings (wstring)? O:-)


KUEHL: kuehl@ramsen.informatik.uni-konstanz.de (Dietmar Kuehl)

Yes. It is written simpler though:

  std::transform(s.begin(), s.end(), s.begin(), std::towupper);

The cast is not needed here because there is only one verson of
'std::towupper' and thus there is no ambiguity. Basically, the same
approach can be extended to arbitrary character types at the cost
of writing a simple template function:

  template <typename T>
  T to_upper(T c) {
    return std::use_facet<std::ctype<T> >(std::locale()).toupper(c);
  }

  std::transform(s.begin(), s.end(), s.begin(), to_upper<T>);

Of course, it is necessary to implement and install the corresponding
'std::ctype<T>' facets for all types 'T' different than 'char' and
'wchar_t'. ... and the performance of the above code sucks! It is not
that bad with the other approach.



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