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digitalmars.D.learn - floating point value rounded to 6digits

reply greatsam4sure <greatsam4sure gmail.com> writes:
double  value = 20.89766554373733;
writeln(value);
//Output =20.8977

How do I output the whole value without using writfln,write or 
format. How do I change this default
Sep 19 2017
parent reply Ivan Kazmenko <gassa mail.ru> writes:
On Tuesday, 19 September 2017 at 20:47:02 UTC, greatsam4sure 
wrote:

 double  value = 20.89766554373733;
 writeln(value);
 //Output =20.8977

 How do I output the whole value without using writfln,write or 
 format. How do I change this default


The default when printing floating-point numbers is to show six 
most significant digits.
You can specify the formatting manually with writefln, for 
example,

     writefln ("%.10f", value);

will print the value with 10 digits after the decimal point.
The writef/writefln function behaves much like printf in C.

See here for a reference on format strings:
https://dlang.org/library/std/format/formatted_write.html#format-string

Ivan Kazmenko.
Sep 19 2017
parent reply greatsam4sure <greatsam4sure gmail.com> writes:
On Tuesday, 19 September 2017 at 21:52:57 UTC, Ivan Kazmenko 
wrote:

 On Tuesday, 19 September 2017 at 20:47:02 UTC, greatsam4sure 
 wrote:

 double  value = 20.89766554373733;
 writeln(value);
 //Output =20.8977

 How do I output the whole value without using writfln,write or 
 format. How do I change this default


 The default when printing floating-point numbers is to show six 
 most significant digits.
 You can specify the formatting manually with writefln, for 
 example,

     writefln ("%.10f", value);

 will print the value with 10 digits after the decimal point.
 The writef/writefln function behaves much like printf in C.

 See here for a reference on format strings:
 https://dlang.org/library/std/format/formatted_write.html#format-string

 Ivan Kazmenko.


I don't  want to use write,writefln or format. I just want to 
change the default
Sep 19 2017
next sibling parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 9/19/17 6:44 PM, greatsam4sure wrote:

 
 I don't  want to use write,writefln or format. I just want to change the 
 default


It's not a bad idea for an enhancement request -- provide default format 
specifiers for a given type.

Currently, there isn't a mechanism for that.

-Steve
Sep 19 2017
prev sibling parent reply Ivan Kazmenko <gassa mail.ru> writes:
On Tuesday, 19 September 2017 at 22:44:06 UTC, greatsam4sure 
wrote:

 On Tuesday, 19 September 2017 at 21:52:57 UTC, Ivan Kazmenko 
 wrote:

 On Tuesday, 19 September 2017 at 20:47:02 UTC, greatsam4sure 
 wrote:

 double  value = 20.89766554373733;
 writeln(value);
 //Output =20.8977

 How do I output the whole value without using writfln,write 
 or format. How do I change this default


 The default when printing floating-point numbers is to show 
 six most significant digits.
 You can specify the formatting manually with writefln, for 
 example,

     writefln ("%.10f", value);

 will print the value with 10 digits after the decimal point.
 The writef/writefln function behaves much like printf in C.

 See here for a reference on format strings:
 https://dlang.org/library/std/format/formatted_write.html#format-string

 Ivan Kazmenko.


 I don't  want to use write,writefln or format. I just want to 
 change the default


Unlikely to be possible.  The built-in data types, such as float 
or double, by definition should not be customizable to such 
degree.

Anyway, under the hood, write uses format with the default format 
specifier "%s" for the values it takes.  So perhaps I'm not quite 
getting what exactly are you seeking to avoid.

For example, consider a helper function to convert the values, 
like the following:

import std.format, std.stdio;
string fmt (double v) {return v.format !("%.10f");}
void main () {
	double x = 1.01;
	writeln (x.fmt); // 1.0100000000
}

Alternatively, you can wrap your floating-point numbers in a thin 
struct with a custom toString():

import std.format, std.stdio;
struct myDouble {
	double v;
	alias v this;
	this (double v_) {v = v_;}
	string toString () {return v.format !("%.10f");}
}
void main () {
	myDouble x = 1.01, y = 2.02, z = x + y;
	writeln (z); // 3.0300000000
}

Ivan Kazmenko.
Sep 19 2017
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 9/19/17 7:28 PM, Ivan Kazmenko wrote:

 On Tuesday, 19 September 2017 at 22:44:06 UTC, greatsam4sure wrote:

 On Tuesday, 19 September 2017 at 21:52:57 UTC, Ivan Kazmenko wrote:

 On Tuesday, 19 September 2017 at 20:47:02 UTC, greatsam4sure wrote:

 double  value = 20.89766554373733;
 writeln(value);
 //Output =20.8977

 How do I output the whole value without using writfln,write or 
 format. How do I change this default


 The default when printing floating-point numbers is to show six most 
 significant digits.
 You can specify the formatting manually with writefln, for example,

     writefln ("%.10f", value);

 will print the value with 10 digits after the decimal point.
 The writef/writefln function behaves much like printf in C.

 See here for a reference on format strings:
 https://dlang.org/library/std/format/formatted_write.html#format-string

 Ivan Kazmenko.


 I don't  want to use write,writefln or format. I just want to change 
 the default


 
 Unlikely to be possible.  The built-in data types, such as float or 
 double, by definition should not be customizable to such degree.
 
 Anyway, under the hood, write uses format with the default format 
 specifier "%s" for the values it takes.  So perhaps I'm not quite 
 getting what exactly are you seeking to avoid.


What he's looking for is a way to globally set "I want all floating 
point values to print this way, unless a more specific specifier is given."

It's not a terrible idea, as any code that's using %s most of the time 
doesn't really care what the result looks like.

I imagine an API like this:

import std.format: setDefaultFormat;
setDefaultFormat!float("%.10f");

-Steve
Sep 19 2017
parent reply Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Tuesday, September 19, 2017 19:35:15 Steven Schveighoffer via 
Digitalmars-d-learn wrote:

 On 9/19/17 7:28 PM, Ivan Kazmenko wrote:

 On Tuesday, 19 September 2017 at 22:44:06 UTC, greatsam4sure wrote:

 On Tuesday, 19 September 2017 at 21:52:57 UTC, Ivan Kazmenko wrote:

 On Tuesday, 19 September 2017 at 20:47:02 UTC, greatsam4sure wrote:

 double  value = 20.89766554373733;
 writeln(value);
 //Output =20.8977

 How do I output the whole value without using writfln,write or
 format. How do I change this default


 The default when printing floating-point numbers is to show six most
 significant digits.
 You can specify the formatting manually with writefln, for example,

     writefln ("%.10f", value);

 will print the value with 10 digits after the decimal point.
 The writef/writefln function behaves much like printf in C.

 See here for a reference on format strings:
 https://dlang.org/library/std/format/formatted_write.html#format-strin
 g

 Ivan Kazmenko.


 I don't  want to use write,writefln or format. I just want to change
 the default


 Unlikely to be possible.  The built-in data types, such as float or
 double, by definition should not be customizable to such degree.

 Anyway, under the hood, write uses format with the default format
 specifier "%s" for the values it takes.  So perhaps I'm not quite
 getting what exactly are you seeking to avoid.


 What he's looking for is a way to globally set "I want all floating
 point values to print this way, unless a more specific specifier is
 given."

 It's not a terrible idea, as any code that's using %s most of the time
 doesn't really care what the result looks like.

 I imagine an API like this:

 import std.format: setDefaultFormat;
 setDefaultFormat!float("%.10f");


The big problem with that is that it does not play nicely at all with pure.
For writeln, that doesn't matter much, since it can't be pure anyway,
because it's doing I/O, but it would matter for stuff like format or
formattedWrite, which IIRC, writeln uses internally.

If what the OP wants is to change what writeln does for floating point
values, the easiest way would be for them to create their own writeln and
use that instead. Then, it can forward to std.stdio.writeln for everything
but floating point values, and for floating point values, it can call
writefln with whatever format specifier gives the desired number of decimal
places.

- Jonathan M Davis
Sep 19 2017
parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 9/19/17 8:04 PM, Jonathan M Davis wrote:

 On Tuesday, September 19, 2017 19:35:15 Steven Schveighoffer via
 Digitalmars-d-learn wrote:

 On 9/19/17 7:28 PM, Ivan Kazmenko wrote:

 On Tuesday, 19 September 2017 at 22:44:06 UTC, greatsam4sure wrote:

 On Tuesday, 19 September 2017 at 21:52:57 UTC, Ivan Kazmenko wrote:

 On Tuesday, 19 September 2017 at 20:47:02 UTC, greatsam4sure wrote:

 double  value = 20.89766554373733;
 writeln(value);
 //Output =20.8977

 How do I output the whole value without using writfln,write or
 format. How do I change this default


 The default when printing floating-point numbers is to show six most
 significant digits.
 You can specify the formatting manually with writefln, for example,

      writefln ("%.10f", value);

 will print the value with 10 digits after the decimal point.
 The writef/writefln function behaves much like printf in C.

 See here for a reference on format strings:
 https://dlang.org/library/std/format/formatted_write.html#format-strin
 g

 Ivan Kazmenko.


 I don't  want to use write,writefln or format. I just want to change
 the default


 Unlikely to be possible.  The built-in data types, such as float or
 double, by definition should not be customizable to such degree.

 Anyway, under the hood, write uses format with the default format
 specifier "%s" for the values it takes.  So perhaps I'm not quite
 getting what exactly are you seeking to avoid.


 What he's looking for is a way to globally set "I want all floating
 point values to print this way, unless a more specific specifier is
 given."

 It's not a terrible idea, as any code that's using %s most of the time
 doesn't really care what the result looks like.

 I imagine an API like this:

 import std.format: setDefaultFormat;
 setDefaultFormat!float("%.10f");


 
 The big problem with that is that it does not play nicely at all with pure.
 For writeln, that doesn't matter much, since it can't be pure anyway,
 because it's doing I/O, but it would matter for stuff like format or
 formattedWrite, which IIRC, writeln uses internally.


That's a perfectly acceptable tradeoff. So:

stdout.setDefaultFormat!float("%.10f");

-Steve
Sep 19 2017