6

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
P0W
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Christian
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    std::setprecision : http://en.cppreference.com/w/cpp/io/manip/setprecision – willll Mar 13 '14 at 15:29
  • ??? NEW CPP programmer why did u add the STL Flag ?? Anyways u can set the precision by `std::setprecision(int )` try `std::cout << std::setprecission(20) << 123456789.12 << endl;` – DOOM Mar 13 '14 at 15:30
  • See http://stackoverflow.com/questions/22177656/convert-double-to-string-with-fixed-point-notation-no-trailing-zeroes-and-witou – Mark Ransom Mar 13 '14 at 15:30
  • What do you want to see in general? Fixed notation and 2 digits after the point? 11 digits in total? – tgmath Mar 13 '14 at 15:44
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    Heh. The smart-alec answer would be to put the number in quotes: `std::cout << "123456789.12";` – Adrian McCarthy Mar 13 '14 at 16:08
  • I just want the trailing zeros to vanish. But I want it to show all digits necessary. So, if there are three digits after the point, I want it to show them. – Christian Mar 13 '14 at 16:15
  • "if there are three digits after the point, I want it to show them" -- zero is a digit. Suppressing trailing zeros is usually both difficult and unwise. – Hot Licks Mar 13 '14 at 16:21

3 Answers3

11

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

P0W
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1

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

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

Community
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herohuyongtao
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    Note, the final digit you get from `+1` isn't to be taken as useful information, except to be able to serialize and restore the value exactly. – Potatoswatter Mar 14 '14 at 12:26
0

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

yosbel
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