I would like to read and write pi as 3,141592
instead of 3.141592
, as using the comma is common in many European countries. How can I accomplish this with iostream
s? In other words
cout << 3.141592;
should print
3,141592
to standard output.
Click Windows/Start and select Control Panel. Select Region and Language and click on the Formats tab. Click on Additional Setting and locate the List Separator. Change the Decimal separator from a full stop (.) to a comma (,).
You should use basic_ios::imbue
to set the preferred locale.
Take a look here: http://www.cplusplus.com/reference/ios/ios_base/imbue/
Locales allow you to use the preferred way by the user, so if a computer in Italy uses comma to separate decimal digits, in the US the dot is still used. Using locales is a Good Practice.
But if you want to explicitly force the use of the comma, take a look here: http://www.cplusplus.com/reference/locale/numpunct/decimal_point/
Here a small example I just made with g++ which enforces the char ',' (passing the separator as template argument is just for fun, not really necessary)
#include <iostream>
#include <locale>
template <class charT, charT sep>
class punct_facet: public std::numpunct<charT> {
protected:
charT do_decimal_point() const { return sep; }
};
int main(int argc, char **argv) {
std::cout.imbue(std::locale(std::cout.getloc(), new punct_facet<char, ','>));
std::cout << "My age is " << 3.1415 << " lightyears.\n";
}
Note that using cout.getloc()
I'm overriding just a single facet in the currently set locale, that is, in the current locale settings of cout, I'm changing only how the punctuation is done.
do_decimal_point
is a virtual function of std::numpunct
that you can redefine to provide your custom separator. This virtual function will be used by numpunct::decimal_point
when printing your number.
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