#include <locale>
#include <iostream>
#include <iomanip>
#include <string>
 
class comma_numpunct : public std::numpunct<char>
{
public:
   comma_numpunct(char thousands_sep, const char* grouping)
      :m_thousands_sep(thousands_sep),
       m_grouping(grouping){}
protected:
   char do_thousands_sep() const{return m_thousands_sep;}
   std::string do_grouping() const {return m_grouping;}
private:
   char m_thousands_sep;
   std::string m_grouping;
};
 
int main()
{
 
    std::locale comma_locale(std::locale(), new comma_numpunct(',', "\03"));
 
    std::cout.imbue(comma_locale);
    std::cout << std::setprecision(7) << std::fixed << 1000000.1234;
}

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