[Mingw-w64-public] toUpper()

Martin Sebor msebor@gmail.com
Wed Jul 1 02:01:00 GMT 2015

On 06/30/2015 05:24 PM, Riot wrote:
>      #include <algorithm>
>      #include <string>
>      std::string str = "Hello World";
>      std::transform(str.begin(), str.end(), str.begin(), std::toupper);

Please note this code is subtly incorrect for two reasons.
There are two overloads of std::toupper:

1) int toupper(int) declared in <ctype.h> (and the equivalent
    std::toupper in <cctype>)
2) template <class T> charT std::toupper(T, const locale&)
    in <locale>

Without the right #include directive, the above may or may
not resolve to "the right" function (which depends on what
declarations the two headers bring into scope).

When it resolves to (2) it will fail to compile.

When it resolves to (1), it will do the wrong thing (have
undefined behavior) at runtime when char is a signed type
and the argument is negative (because (1) is only defined
for values between -1 and UCHAR_MAX).

But the question is about converting std::wstring to upper
case and the above uses a narrow string. For wstring, the
std::ctype<wchar_t>::toupper() function or its convenience
non-member template function can be used.

> See also: http://www.cplusplus.com/reference/locale/toupper/

This is one possible way to do it. Another approach is along
these lines:

    std::locale loc (...);
    std::wstring wstr = L"...";
    const std::ctype<wchar_t> &ct =
        std::use_facet<std::ctype<wchar_t> >(loc);
    ct.toupper (&wstr[0], &wstr[0] + wstr.size());


> This may also help in future: http://lmgtfy.com/?q=c%2B%2B+toupper
> -Riot
> On 30 June 2015 at 23:58,  <papa@arbolone.ca> wrote:
>> I would like to write a function to capitalize letters, say...
>> std::wstring toUpper(const std::wstring wstr){
>> for ( auto it = wstr.begin(); it != wstr.end(); ++it){
>>          global_wapstr.append(std::towupper(&it));
>> }
>> }
>> This doesn’t work, but doesn’t the standard already have something like
>> std::wstring::toUpper(...)?
>> Thanks in advance
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