今天才知道原來 0.1 + 0.2 不是 0.3
相關網站：
http://0.30000000000000004.com/
| Language | Code | Result |
|---|---|---|
| C |
#include<stdio.h>
int main(int argc, char** argv) {
printf("%.17f\n", .1+.2);
return 0;
}
|
0.30000000000000004 |
| C++ |
#include <iomanip> std::cout << setprecision(17) << 0.1 + 0.2 << std.endl; |
0.30000000000000004 |
| PHP | echo .1 + .2; |
0.3 |
| PHP converts 0.30000000000000004 to a string and shortens it to “0.3”. To achieve the desired floating point result, adjust the precision ini setting: ini_set(“precision”, 17). | ||
| MySQL | SELECT .1 + .2; |
0.3 |
| Postgres | SELECT select 0.1::float + 0.2::float; |
0.3 |
| Delphi XE5 | writeln(0.1 + 0.2); |
3.00000000000000E-0001 |
| Erlang | io:format("~w~n", [0.1 + 0.2]). |
0.30000000000000004 |
| Elixir | IO.puts(0.1 + 0.2) |
0.30000000000000004 |
| Ruby | puts 0.1 + 0.2And puts 1/10r + 2/10r |
0.30000000000000004 And 3/10 |
| Ruby supports rational numbers in syntax with version 2.1 and newer directly. For older versions use Rational. Ruby also has a library specifically for decimals: BigDecimal. |
||
| Python 2 | print(.1 + .2)And float(decimal.Decimal(".1") + decimal.Decimal(".2")) And.1 + .2 |
0.3 And 0.3 And 0.30000000000000004 |
| Python 2’s “print” statement converts 0.30000000000000004 to a string and shortens it to “0.3”. To achieve the desired floating point result, use print(repr(.1 + .2)). This was fixed in Python 3 (see below). | ||
| Python 3 | print(.1 + .2)And .1 + .2 |
0.30000000000000004 And 0.30000000000000004 |
| Lua | print(.1 + .2) |
0.3 0.30000000000000004 |
| JavaScript | document.writeln(.1 + .2); |
0.30000000000000004 |
| Java | System.out.println(.1 + .2);And System.out.println(.1F + .2F); |
0.30000000000000004 And 0.3 |
| Julia | .1 + .2 |
0.30000000000000004 |
Julia has built-in rational numbers support and also a built-in arbitrary-precision BigFloat data type. To get the math right, 1//10 + 2//10 returns 3//10. |
||
| Clojure | (+ 0.1 0.2) |
0.30000000000000004 |
Clojure supports arbitrary precision and ratios. (+ 0.1M 0.2M) returns 0.3M, while (+ 1/10 2/10) returns 3/10. |
||
| C# | Console.WriteLine("{0:R}", .1 + .2); |
0.30000000000000004 |
| GHC (Haskell) | 0.1 + 0.2 |
0.30000000000000004 |
Haskell supports rational numbers. To get the math right, (1 % 10) + (2 % 10) returns 3 % 10. |
||
| Hugs (Haskell) | 0.1 + 0.2 |
0.3 |
| bc | 0.1 + 0.2 |
0.3 |
| Nim | echo(0.1 + 0.2) |
0.3 |
| Gforth | 0.1e 0.2e f+ f. |
0.3 |
| dc | 0.1 0.2 + p |
.3 |
| Racket (PLT Scheme) | (+ .1 .2)And (+ 1/10 2/10) |
0.30000000000000004 And 3/10 |
| Rust |
extern crate num;
use num::rational::Ratio;
fn main() {
println!(.1+.2);
println!("1/10 + 2/10 = {}", Ratio::new(1, 10) + Ratio::new(2, 10));
}
|
0.30000000000000004 3/10 |
| Rust has rational number support from the num crate. | ||
| Emacs Lisp | (+ .1 .2) |
0.30000000000000004 |
| Turbo Pascal 7.0 | writeln(0.1 + 0.2); |
3.0000000000E-01 |
| Common Lisp | * (+ .1 .2)And * (+ 1/10 2/10) |
0.3 And 3/10 |
| Go |
package main
import "fmt"
func main() {
fmt.Println(.1 + .2)
var a float64 = .1
var b float64 = .2
fmt.Println(a + b)
fmt.Printf("%.54f\n", .1 + .2)
}
|
0.3 0.30000000000000004 0.299999999999999988897769753748434595763683319091796875 |
| Go numeric constants have arbitrary precision. | ||
| Objective-C | 0.1 + 0.2; |
0.300000012 |
| OCaml | 0.1 +. 0.2;; |
float = 0.300000000000000044 |
| Powershell | PS C:\>0.1 + 0.2 |
0.3 |
| Prolog (SWI-Prolog) | ?- X is 0.1 + 0.2. |
X = 0.30000000000000004. |
| Perl 5 | perl -E 'say 0.1+0.2'perl -e 'printf q{%.17f}, 0.1+0.2' |
0.3 0.30000000000000004 |
| Perl 6 | perl6 -e 'say 0.1+0.2'perl6 -e 'say sprintf(q{%.17f}, 0.1+0.2)'perl6 -e 'say 1/10+2/10' |
0.3 0.30000000000000000 0.3 |
| Perl 6, unlike Perl 5, uses rationals by default, so .1 is stored something like { numerator => 1, denominator => 10 }.. | ||
| R | print(.1+.2) |
0.3 0.300000000000000044 |
| scala | scala -e 'println(0.1 + 0.2)'And scala -e 'println(0.1F + 0.2F)' Andscala -e 'println(BigDecimal("0.1") + BigDecimal("0.2"))' |
0.30000000000000004 And 0.3 And 0.3 |
| Smalltalk | 0.1 + 0.2. |
0.30000000000000004 |
| Swift | 0.1 + 0.2NSString(format: "%.17f", 0.1 + 0.2) |
0.3 0.30000000000000004 |
| D |
import std.stdio;
void main(string[] args) {
writefln("%.17f", .1+.2);
writefln("%.17f", .1f+.2f);
writefln("%.17f", .1L+.2L);
}
|
0.29999999999999999 0.30000001192092896 0.30000000000000000 |
| ABAP | WRITE / CONV f( '.1' + '.2' ).And WRITE / CONV decfloat16( '.1' + '.2' ). |
3.0000000000000004E-01 And 0.3 |