如何制作“std :: cout << 123456789.12”打印“123456789.12”？

Question

How do I make

std::cout << 123456789.12

print this:

123456789.12

It always prints this:

1.23457e+008

I know that I have to play with the flags, but I cant quite figure out the right combination. If I set the fixed flag, it prints

123456789.120000

Answer 1

How to ... ?

One way :-

#include <iostream>
#include <iomanip>

int main() {
    double f =123456789.12;
    std::cout << std::fixed << std::setprecision(2) << f << '\n';
    return 0;
}

See here

Please look for appropriate references

Answer 2

You can use:

#include <iostream>
#include <limits>
using namespace std;

int main() {
    double c = 123456789.12;
    cout.precision(numeric_limits<double>::digits10 + 1);
    cout << c << endl;

    return 0;
}

Basically the limits package has traits for all the build-in types. One of the traits for floating point numbers ( float/double/long double ) is the digits10 attribute . This defines the accuracy of a floating point number in base 10.

See it live: http://ideone.com/Ity9m7

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To read on, check out another similar question: How do I print a double value with full precision using cout?

Answer 3

You can use boost::lexical_cast as follow:

#include <boost/lexical_cast.hpp>

std::cout << boost::lexical_cast<std::string>(123456789.12);

more info can be found in http://www.boost.org/doc/libs/1_55_0/doc/html/boost_lexical_cast.html