STRTOF的精确问题 [英] Precision Issue with STRTOF
问题描述
亲爱的小组
我在使用STRTOF将文本字符串转换为
浮点数时遇到精度问题。例如，有时将文本串736.00000
终止字符串。有谁知道为什么会发生这种情况以及
专门用来避免这种情况。这对我正在写的申请表非常关键。
谢谢
Marcus D. Jacobs
Dear Group
I am encountering a precision issue while converting a text string to
a float using STRTOF. For example, at times a text string "736.00000"
(quotation marks added) is converted to "736.00001". I have null
terminated the strings. Does anyone know why does this happen and how
specifically to avoid this. This is quite critical to an applicaiton
that I am writing.
Thanks
Marcus D. Jacobs
推荐答案
ma ******* @ hotmail.com （Marcus Jacobs）写道：
ma*******@hotmail.com (Marcus Jacobs) writes:
我在使用STRTOF将文本字符串转换为浮点数时遇到精度问题。例如，有时文本串736.00000
（添加引号）被转换为736.00001。我没有
终止字符串。有谁知道为什么会发生这种情况以及如何特别避免这种情况。这对我正在撰写的申请来说非常关键。
I am encountering a precision issue while converting a text string to
a float using STRTOF. For example, at times a text string "736.00000"
(quotation marks added) is converted to "736.00001". I have null
terminated the strings. Does anyone know why does this happen and how
specifically to avoid this. This is quite critical to an applicaiton
that I am writing.
您应该阅读常见问题解答。
-
有些编程实践会产生错误;
这个就像拨打一个800号码
并且错误传递给你的门。 br />
--Steve McConnell
You should read the FAQ.
--
"Some programming practices beg for errors;
this one is like calling an 800 number
and having errors delivered to your door."
--Steve McConnell
Marcus Jacobs写道：
Marcus Jacobs wrote:
我在转换时遇到精度问题使用STRTOF的文本字符串
浮点数。例如，有时文本串736.00000
（添加引号）被转换为736.00001。我没有
终止字符串。有谁知道为什么会发生这种情况以及如何特别避免这种情况。这对于我正在编写的应用程序非常关键。
I am encountering a precision issue while converting a text string to
a float using STRTOF. For example, at times a text string "736.00000"
(quotation marks added) is converted to "736.00001". I have null
terminated the strings. Does anyone know why does this happen and how
specifically to avoid this. This is quite critical to an applicaiton
that I am writing.
您是否尝试过编写这样的小测试程序（未经测试）？
#include< stdio.h>
main（）{
float x = 736.0;
printf（"％f\ n"，（double）x）;
}
你可能得到类似的结果。 Float是低精度的
类型。 Double是高精度型。使用双倍。
-
Tom Zych
这个电子邮件地址将在某个时候到期以阻止垃圾邮件发送者。
永久地址：echo''g******@cbobk.pbz''| rot13
Did you try writing a little test program like this (not tested)?
#include <stdio.h>
main() {
float x = 736.0;
printf("%f\n", (double) x);
}
You''ll probably get similar results. Float is the low-precision
type. Double is the high-precision type. Use double.
--
Tom Zych
This email address will expire at some point to thwart spammers.
Permanent address: echo ''g******@cbobk.pbz'' | rot13
Marcus Jacobs写道：
Marcus Jacobs wrote:
亲爱的小组
我在转换时遇到精确问题使用STRTOF的文本字符串
浮点数。例如，有时文本串736.00000
（添加引号）被转换为736.00001。我没有
终止字符串。有谁知道为什么会发生这种情况以及如何特别避免这种情况。这对于我正在编写的应用程序来说非常关键。
Dear Group
I am encountering a precision issue while converting a text string to
a float using STRTOF. For example, at times a text string "736.00000"
(quotation marks added) is converted to "736.00001". I have null
terminated the strings. Does anyone know why does this happen and how
specifically to avoid this. This is quite critical to an applicaiton
that I am writing.
请注意，C区分大小写。函数的名称是''strtof''，而不是''STRTOF''。
strtof（）返回一个浮点数。一个浮点数不需要超过6位数的
精度。您报告的值736.00001除了缩放（尾数）之外，还有大约27位信息
。你怎么知道这个值有那些精确的8位十进制数字？如果你只限于打印
只有数据中的信息，你会做得更好。
#include< stdio.h>
#include< math.h>
void showfloat（x）
{
printf（"％。* g"，FLT_DIG，x）;
}
-
Martin Ambuhl
Note that C is case-sensitive. The function''s name is ''strtof'', not ''STRTOF''.
strtof() returns a float. A float need not have more than 6 digits of
precision. The value you report "736.00001" has some 27 bits of information
apart from scaling ("mantissa"). How do you know that the value has those
8 decimal digits of precision? If you would restrict yourself to printing
only the information in the data, you would do better.
#include <stdio.h>
#include <math.h>
void showfloat(x)
{
printf("%.*g", FLT_DIG, x);
}
--
Martin Ambuhl
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