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C++ oftream decimal precision

Posted on 2008-10-15
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Last Modified: 2013-11-05
Having trouble figuring out how to set decimal precision when writing ofstream to .txt file. When I open the text file produced by the following code the result is "0.111111" and not the full number of expected decimal places.


ofstream OF;
OF.open("file_name.txt");
 
double n = 0.1111111111111111;
OF << n << endl;

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Question by:Fippy_Darkpaw
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3 Comments
 
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jkr earned 105 total points
ID: 22722505
<iomanip> will help you here:


#include <iomanip>
#uncing namespace std;
 
ofstream OF;
OF.open("file_name.txt");
 
size_t prec = 5;
double n = 0.1111111111111111;
OF << setprecision(prec) << n << endl;

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by:jkr
ID: 22722518
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by:itsmeandnobodyelse
itsmeandnobodyelse earned 20 total points
ID: 22722904
>>>> #uncing namespace std;

Maybe

 using namespace std;

is better  ;-)

To add to above comment:

When including iomanip you also could use the ios members fixed and scientific to specify how the floating point was displayed. Note if using fixed the setprecision will determine the number of digits after the decimal point. Otherwise it is the number of significant digits.

   OF << fixed << setprecision(prec) << n << endl;

Note, it maybe dependent on the compiler but I had made the experience that if ommitting the 'fixed' the precision specifies the number of significant digits to display. That is different to that the docs say (and it may have been some time when I lastly tested it).
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