来信收到，谢谢！
---原始邮件---
From:"qt-creator-request"<[email protected]>;
Date:2010年7月11日(星期天) 晚上6:00
To:"qt-creator"<[email protected]>;
Subject:Qt-creator Digest, Vol 22, Issue 18
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Today's Topics:
1. tofloat() function gives inappropriate results (Ashish Vats)
2. Re: tofloat() function gives inappropriate results (David Dibben)
3. Re: tofloat() function gives inappropriate results (Andre Poenitz)
4. Nokia SDK and State Machine Framework on linux
(Antonio Cano G?mez)
5. Re: Nokia SDK and State Machine Framework on linux (Alex T.)
----------------------------------------------------------------------
Message: 1
Date: Sat, 10 Jul 2010 16:28:23 +0530
From: "Ashish Vats" <[email protected]>
Subject: [Qt-creator] tofloat() function gives inappropriate results
To: <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
I am using QT4.5 , I want to convert the string value to float so I have used
function tofloat(). But the results i am getting are not accurate.
For example : If the string value is 7.6 then the output of function to float
is 7.5999...
Regards
Ashish
Larsen & Toubro Limited
Electrical & Electronics Division - EBG
http://www.LNTEBG.com
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Message: 2
Date: Sat, 10 Jul 2010 21:46:00 +0900
From: David Dibben <[email protected]>
Subject: Re: [Qt-creator] tofloat() function gives inappropriate
results
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
Hi Ashish,
On 10/07/2010 19:58, Ashish Vats wrote:
> I am using QT4.5 , I want to convert the string value to float so I have
> used function tofloat(). But the results i am getting are not accurate.
> For example : If the string value is 7.6 then the output of function to
> float is 7.5999...
Firstly, I am think this might not be the right list for this question.
I would try Qt-Interest instead.
But to answer your question. The problem is not with QString::toFloat
but the nature of floating point numbers. A float cannot represent 7.6
exactly, so you will always get this type of error
For example, try this little program:
int main()
?
??? float x = 7.6f;
printf(" %16.15f \n", x);
double y = 7.6;
printf(" %16.15f \n", y);
reurn 0;
?
This does not use Qt's QString at all, and I get:
7.599999904632568
7.600000000000000
When using a float, you won't get 7.6. I would try using a double
instead. That will give a better representation, but there will still be
strings that do not get converted exactly. Depending on what you want to
do with the numbers that may or may not matter.
--
David Dibben
Web: http://www.daviddibben.com
Mail: [email protected]
------------------------------
Message: 3
Date: Sat, 10 Jul 2010 15:37:41 +0200
From: Andre Poenitz <[email protected]>
Subject: Re: [Qt-creator] tofloat() function gives inappropriate
results
To: [email protected]
Message-ID: <20100710133741.ga2...@localhost>
Content-Type: text/plain; charset=us-ascii
On Sat, Jul 10, 2010 at 04:28:23PM +0530, Ashish Vats wrote:
> I am using QT4.5 , I want to convert the string value to float so I
> have used function tofloat(). But the results i am getting are not
> accurate.
This has nothing to do with Qt Creator, not even wit Qt and only
marginally with C++, it's just the way floating point numbers work.
> For example : If the string value is 7.6 then the output of function
> to float is 7.5999...
The value 7.6 has no finite representation in base 2. It's something
like 111.1001100110011... with the 0011 part repeating infinitely.
Whenever you try to store that form in some finite memory it needs to be
rounded or cut off at some point. So the value stored is _not_ 7.6 but
something close to it, and there is no way to reconstruct the original
value, as the cut-off part is permanently lost.
There are several approaches to avoid this "loss" (like using fixed
point arithmetic, rounding, or not converting to floating point at all).
Andre'
------------------------------
Message: 4
Date: Sun, 11 Jul 2010 08:12:59 +0200
From: Antonio Cano G?mez <[email protected]>
Subject: [Qt-creator] Nokia SDK and State Machine Framework on linux
To: [email protected]
Message-ID: <1278828779.1543.8.ca...@nokia-n900>
Content-Type: text/plain; charset="utf-8"
Hi,
I downloaded the Nokia SDK for linux 64 and tried to compile an aplication for
symbyan.
This application compiled correctly for Nokia SDK in Windows.
But when I try to compile the same source code for Nokia SDK in Linux, I
receive the error that the library for the state machine is not available.
Please, could someone tell me if there is to way to include this library or
when it is going to be offivially available for linux version.
Thanks,
Toni
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Message: 5
Date: Sun, 11 Jul 2010 09:47:12 +0300
From: "Alex T." <[email protected]>
Subject: Re: [Qt-creator] Nokia SDK and State Machine Framework on
linux
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Who is giving you an error? A compiler or linker? This library is in QtCore.
Probably you have to check your CFLAGS/CXXFLAGS and/or LDFLAGS.
2010/7/11 Antonio Cano G?mez <[email protected]>
> Hi,
>
> I downloaded the Nokia SDK for linux 64 and tried to compile an aplication
> for symbyan.
>
> This application compiled correctly for Nokia SDK in Windows.
>
> But when I try to compile the same source code for Nokia SDK in Linux, I
> receive the error that the library for the state machine is not available.
>
> Please, could someone tell me if there is to way to include this library or
> when it is going to be offivially available for linux version.
>
> Thanks,
>
> Toni
>
>
> -------------------------------------------------------------- Ovi Mail:
> Making email access easy
> http://mail.ovi.com
>
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