473,734 Members | 2,764 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

Unexpected 'setprecision' behaviour.....

Hi All,

I am new to C++ programming. I encounter an unexpected behavior of
'setprecision'.

The code snippet is :

#include <iostream.h>
#include <stdio.h>
#include <iomanip.h>

int main()
{
long double ld=1234567890.1 234567898;

int prec = 0;

prec = cout.precision( );
cout<<"Precisio n : "<<prec<<en dl;

cout.flags(ios: :fixed);
cout << setprecision(10 ) << ld << endl;

prec = cout.precision( );
cout<<"Precisio n : "<<prec<<en dl;

return 0;
}
The output I was expecting was :

Precision : 6
1234567890.1234 567898
Precision : 10

But the output that was produced is :

Precision : 6
1234567890.1234 567000
Precision : 10
What happened to the last 3 digits of the variable I am trying to
print.
Why is it filling zeros in the last three places? Is there any reasong
behind that?

Please enlighten me on this issue.

Thanks in Advance,
Mahesh K U

Aug 7 '07 #1
2 1811
AG
Hi Mahesh,

long double number are still represented on a finite number of bits,
which gives a limit to the representation of real numbers. You have
reached this limit.

try this for a first understanding of the problem :

http://en.wikipedia.org/wiki/IEEE_754

AG.

Aug 7 '07 #2
On Aug 7, 8:33 am, mahesh.kanaka.. .@gmail.com wrote:
I am new to C++ programming. I encounter an unexpected behavior of
'setprecision'.
The code snippet is :
#include <iostream.h>
#include <stdio.h>
#include <iomanip.h>
int main()
{
long double ld=1234567890.1 234567898;
int prec = 0;
prec = cout.precision( );
cout<<"Precisio n : "<<prec<<en dl;
cout.flags(ios: :fixed);
cout << setprecision(10 ) << ld << endl;
prec = cout.precision( );
cout<<"Precisio n : "<<prec<<en dl;
return 0;
}
The output I was expecting was :
Precision : 6
1234567890.1234 567898
Precision : 10
Why?
But the output that was produced is :
Precision : 6
1234567890.1234 567000
Precision : 10
What happened to the last 3 digits of the variable I am trying to
print.
They were never there. The original number you specified is
doubtlessly not representable as a floating point number.
You're library implementation decided to output zeros rather
than random noise once it has output everything significant.
Why is it filling zeros in the last three places? Is there any reasong
behind that?
See http://docs.sun.com/source/806-3568/ncg_goldberg.html. It's
the reference for floating point; until you've understood it,
you shouldn't be using floating point.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

Aug 7 '07 #3

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

2
8721
by: Woodster | last post by:
I am using the std::setprecision function to format variables of type double in a string however I am unsure how to stop this appearing in scientific notation. For example std::stringstream buffer; buffer << setprecision(1) << 40.0 << "° C";
2
2168
by: Gerhard Esterhuizen | last post by:
Hi, I am observing unexpected behaviour, in the form of a corrupted class member access, from a simple C++ program that accesses an attribute declared in a virtual base class via a chain of virtual method calls. To further complicate (or perhaps simplify) matters, some compilers (GCC and MingW) produce the expected behaviour, while others (MSVS 7.1) do not. I can only offer two explanations for my observations: 1. The Microsoft...
9
2180
by: Jeff Louie | last post by:
In C# (and C++/cli) the destructor will be called even if an exception is thrown in the constructor. IMHO, this is unexpected behavior that can lead to an invalid system state. So beware! http://www.geocities.com/jeff_louie/oop30.htm Regards, Jeff *** Sent via Developersdex http://www.developersdex.com ***
1
2673
by: Gary Wessle | last post by:
hi the code below is giving me what I want but it is very ugly. and will not work for a long list of different length numbers. could you please look at it and comment. thank you the desired output is: 0.555504 of an inch foreach 12.55
3
2498
by: Anjo Gasa | last post by:
I'm having some cases where setprecision in combination with iostreams gives some unepected behavior. Consider the following program: #include <iostream> #include <iomanip> int _tmain(int argc, _TCHAR* argv) { float value = 0.063397526741027832;
7
12504
by: jacek.dziedzic | last post by:
Hello! Can someone tell me what the expected output of the following program is? #include <fstream> #include <iomanip> using namespace std;
3
5063
by: PengYu.UT | last post by:
Hi, I setprecision to be 100 for both cases. I'm wondering why the number of digits are different. Also, for a double number, I think any digits that are longer than 15 (or 16) are not meaningful, because it exceed the double number's precision limit. Even if I setprecision to be 100, shall it truncate the number to be of 15(or 16) digits?
1
4881
by: jthep | last post by:
Hi, I'm converting codes that I worked with in C to C++ and having a problem with setprecision. At first the code worked, then I made some changes. When the changes didn't work I wrote it back to how it was before and now it's not working. I keep getting the error message where setprecision is undefined. Can anyone help plz. #include <iostream> using namespace std; float convertFtoC(int temperature); int roundUpNextMultiple(int...
2
5519
by: victoryusami | last post by:
I'm not 100% sure whats even going on, but I'm working on a C++ assignment for school, and its a road trip program #include <iostream> #include <iomanip> using namespace std; char const METRIC = 'M'; // Input read as metric char const ENGLISH = 'E'; // Input read as english char const QUIT = 'Q'; // Input read to quit program char const QUIT2 = 'q'; // Input read to quit program
0
8946
marktang
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look ! Part I. Meaning of...
0
8776
by: Hystou | last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it. First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
0
9449
Oralloy
by: Oralloy | last post by:
Hello folks, I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>". The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed. This is as boiled down as I can make it. Here is my compilation command: g++-12 -std=c++20 -Wnarrowing bit_field.cpp Here is the code in...
1
9236
by: Hystou | last post by:
Overview: Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
0
8186
agi2029
by: agi2029 | last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own.... Now, this would greatly impact the work of software developers. The idea...
0
6031
by: conductexam | last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one. At the time of converting from word file to html my equations which are in the word document file was convert into image. Globals.ThisAddIn.Application.ActiveDocument.Select();...
0
4550
by: TSSRALBI | last post by:
Hello I'm a network technician in training and I need your help. I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs. The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols. I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
2
2724
muto222
by: muto222 | last post by:
How can i add a mobile payment intergratation into php mysql website.
3
2180
bsmnconsultancy
by: bsmnconsultancy | last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.