how to format out in c++? - c++

Question

I know how to use printf() to format output of float, for example:
float i = 1;
printf("%.2f", i);
but how to format the output using cout to output 2 digits after "."?

Answer 1

Following will do:
std::cout<<std::fixed<<std::setprecision(2)<<i;
You will also need to include iomanip

Answer 2

#include <iostream>
#include <iomanip>
using namespace std;
int main() {
cout << setprecision(2) << setiosflags(ios::fixed) << 3.141592 << endl;
}
use setprecision().

Answer 3

A red herring is to use std::setprecision on its own:
float f = 3.1415;
std::cout << std::setprecision(2) << f;
However, "precision" is not the same as "number of decimal places", as shown in this example.
Fortunately, and somewhat confusingly, switching the stream to "fixed-point" display changes the meaning of std::setprecision to something more akin to "setDecimalPlaces".
So, you can write this:
float f = 3.1415;
std::cout << std::fixed << std::setprecision(2) << f;

Answer 4

Boost format helps:
std::cout << boost::format("%.2f") % i;

Answer 5

#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
double x = 800000.0/81.0;
cout << setiosflags(ios::fixed) << setprecision(2) << x;
return 0;
}

Answer 6

hope this helps.........
#include <iostream>
#include <iomanip>
using namespace std;
int main () {
double f =3.14159;
cout << setprecision (5) << f << endl;
cout << setprecision (9) << f << endl;
cout << fixed;
cout << setprecision (5) << f << endl;
cout << setprecision (9) << f << endl;
return 0;
}
output..
> 3.1416
> 3.14159
> 3.14159
> 3.141590000

Answer 7

cout << ffmt(0, 2) << i;
Where ffmt is defined as:
class ffmt
{
int width;
int precision;
public:
ffmt( int width, int precision )
: width( width )
, precision( precision )
{
}
friend std::ostream& operator<<(
std::ostream& dest,
ffmt const& manip )
{
dest.setf( std::ios_base::fixed, std::ios_base::floatfield );
dest.width( width );
dest.precision( precision );
}
};
You can also extend this to restore format state at the end of the full
expression; it's not too important for floating point, because most of
the time, you'll use the manipulator in front of each output, but a
manipulator which leaves the stream outputting hex is likely to lead to
surprising output later.
As a general rule, except for quicky demo or test programs, you almost
never use the standard manipulators, other that std::setw. For that
matter, in a lot of applications, you'll even avoid things like ffmt,
in favor of specific manipulators for each semantic value you have.