manipulator, C++ (vc++)

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#include <iostream>
#include <iomanip>
#include <string>

namespace manip
{
    namespace detail
    {
        template < typename CHAR, typename TRAITS = std::char_traits<CHAR>,
                   typename ALLOC = std::allocator<CHAR> >
        struct centre
        {
            template < typename STR_OR_CSTR >
            centre( const STR_OR_CSTR& str, std::size_t width ) : str(str), width(width) {}

std::basic_string<CHAR,TRAITS,ALLOC> str ;
            std::size_t width ;

template < typename OSTREAM >
            friend OSTREAM& operator<< ( OSTREAM& stm, const centre& cntr )
            {
                std::size_t padl = 0 ;
                std::size_t padr = 0 ;
                if( cntr.width > cntr.str.size() )
                {
                    padl = ( cntr.width - cntr.str.size() ) / 2 ;
                    padr = padl + ( cntr.width - cntr.str.size() ) % 2 ;
                }

for( std::size_t i = 0 ; i < padl ; ++i ) stm << stm.widen(' ') ;
                stm << cntr.str ;
                for( std::size_t i = 0 ; i < padr ; ++i ) stm << stm.widen(' ') ;

return stm ;
            }
        };
    }

template < typename CHAR > // centre c-style strings
    detail::centre<CHAR> centre( const CHAR* cstr, std::size_t width )
    { return { cstr, width } ; }

template < typename CHAR, typename TRAITS, typename ALLOC > // centre C++ strings
    detail::centre<CHAR,TRAITS,ALLOC> centre( const std::basic_string<CHAR,TRAITS,ALLOC>& str, std::size_t width )
    { return { str, width } ; }

template < typename NUM_TYPE > // centre numbers (output as narrow characters)
    typename std::enable_if< std::is_arithmetic<NUM_TYPE>::value,
                             detail::centre<char> >::type
    centre( const NUM_TYPE& number, std::size_t width )
    { return { std::to_string(number), width } ; }

template < typename NUM_TYPE > // centre numbers (output as wide characters)
    typename std::enable_if< std::is_arithmetic<NUM_TYPE>::value,
                             detail::centre<wchar_t> >::type
    wcentre( const NUM_TYPE& number, std::size_t width )
    { return { std::to_wstring(number), width } ; }
}

int main()
{
    using namespace std::literals ;

std::cout << '|' << manip::centre( "abcde", 20 ) << "|\n"
              << '|' << manip::centre( "fghijk"s, 20 ) << "|\n"
              << '|' << manip::centre( "lmnopqr"s, 20 ) << "|\n"
              << '|' << manip::centre( -123.45, 20 ) << "|\n" ;

std::wcout << L'|' << manip::centre( L"jklmno", 20 ) << L"|\n"
               << L'|' << manip::centre( L"pqrstuv"s, 20 ) << L"|\n"
               << L'|' << manip::centre( L"lmnopqr"s, 20 ) << L"|\n"
               << L'|' << manip::wcentre( -123.45, 20 ) << "|\n" ;
}

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Compilation time: 1,83 sec, absolute running time: 0,22 sec, absolute service time: 2,06 sec