浮点比较问题 [英] Floating Point comparison problem
问题描述
下个月，我将开始研究一个名为CAT ++的基于C ++的软件，它将在C ++中提供类似FORTRAN的数组，并将在
中使用。因此将在很大程度上依赖于
数值计算。我正在阅读29.16和29.17节的常见问题解答：
http://www.parashift.com/c++-faq-lit...html#faq-29.16
作为测试，我刚在Linux，GCC 4.2.2上试过这个程序，它给了我2
不同的结果：
#include< iostream>
#include< string>
#include< vector>
int main（）
{
const double x = 0.05;
const double y = 0.07;
const double z = x + y;
const double key_num = x + y;
if（key_num == z）
{
std :: cout<< " == \ n";
}
else
{
std :: cout< < "！= \ n";
}
返回0;
}
==========输出============
/ home / arnuld / programs $ g ++ -ansi - 迂腐-Wall -Wextra test2.cpp
/ home / arnuld / programs $ ./a.out
==
/ home / arnuld / program $
总是输出==，现在我将key_num更改为：
const double key_num = 0.12;
，这个程序现在总是输出！=
/ home / arnuld / programs $ g ++ -ansi -pedantic -Wall -Wextra test2.cpp
/ home / arnuld / programs $ ./a.out
！=
/ home / arnuld / programs $
如常见问题解答浮动-Point是不准确的，但是我的项目非常重要，因为我正在考虑停止开发使用C ++中的软件并且仅仅使用FORTRAN来实现这个特定的 b
br />
申请特殊域名。
-
http://lispmachine.wordpress.com/
< blockquote> g ++ -ansi -pedantic -Wall -Wextra test2.cpp
/ home / arnuld / programs
./ a.out
==
/ home / arnuld / programs
总是输出==，现在我将key_num更改为：
const double key_num = 0.12;
此程序现在总是输出！=
/家庭/ arnuld /方案
Next month I will start to work on a C++ based Software named CAT++ which
is going to provide FORTRAN like arrays in C++ and will be used within
Scientific Community and hence will heavily depend on
Numerical-Computations. I was reading 29.16 ans 29.17 sections of FAQs:
http://www.parashift.com/c++-faq-lit...html#faq-29.16
as a test, I just tried this program on Linux, GCC 4.2.2 and it gave me 2
different results:
#include <iostream>
#include <string>
#include <vector>
int main()
{
const double x = 0.05;
const double y = 0.07;
const double z = x + y;
const double key_num = x + y;
if( key_num == z )
{
std::cout << "==\n";
}
else
{
std::cout << "!=\n";
}
return 0;
}
========== OUTPUT ============
/home/arnuld/programs $ g++ -ansi -pedantic -Wall -Wextra test2.cpp
/home/arnuld/programs $ ./a.out
==
/home/arnuld/programs $
it always outputs == , Now i changed key_num to this:
const double key_num = 0.12;
and this program now always outputs !=
/home/arnuld/programs $ g++ -ansi -pedantic -Wall -Wextra test2.cpp
/home/arnuld/programs $ ./a.out
!=
/home/arnuld/programs $
As FAQ explains Floating-Point is inaccurate but my project is heavily
oriented towards number-crunching, so I was thinking of stop developing
that sofwtare in C++ and simply use FORTRAN for this specific
application in a special domain.
--
http://lispmachine.wordpress.com/
g++ -ansi -pedantic -Wall -Wextra test2.cpp
/home/arnuld/programs
./a.out
==
/home/arnuld/programs
it always outputs == , Now i changed key_num to this:
const double key_num = 0.12;
and this program now always outputs !=
/home/arnuld/programs
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