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How to preserve data integrity while minimizing the transmission size

- by user1500578

we have sensors in the wild that send their data to a server every day via TCP/IP, either through 3G or through satellite for the physical layer. The sensors can automatically switch from one to the other depending on their location and the quality of the signal with the local 3G operator. Given that the 3G and satellite communications are very expensive, we want to minimize the amount of data to send. But also, we want to protect ourselves from lost data. What would be the best strategy to ensure with reasonable certainty that the integrity of our data is preserved, while minimizing the amount of redundancy, i.e the amount of data transmitted ? I've read about the zfec codec, but I'm not sure if we need to transmit all the chunks, or if we need to send a hash code along each chunk.

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PHP - Loop thru recordset and fire event each n rows

- by Luciano

I'm looking for the right logic to loop thru a recordset and fire an event each n times. Searching on Google i've found some discussion on similar situations, but it seems that solutions don't fits my needs. Let's say i have a recordset of 22 rows. I want to loop thru each row and launch a function on the 4th, the 8th, the 12th and so on... Using the modulus operator as shown in this answer, if($i % 4 == 0), i get the event fired each 4 rows, but 22 its not a multiple of 4 so the event is fired till the 20th row and then nothing. Maybe i need to make a division counting rows in 'excess'? Since the recordset will be between 50 and 200 rows i think its not necessary run multiple query of 4 rows, am I wrong? Thanks in advance!

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Alfa AWUSO36H 1W dysfunctional driver

- by BrainStorm

I recently purchased an Alfa AWUSO36H 1W wireless USB adapter for my notebook, in order to improve signal strength and quality. I'm currently using Linux Mint 11, and the it uses the RTL8187 driver for this adapter, I'm also using a 4dbi antenna, though I have others. The problem is that this adapter does exactly the opposite of what it should, actually my internal Broadcom BCM4313 adapter works way better than the alfa. Browsing is slow, some network applications don't even work, pings against Google.com on the internal adapter runs smooth, while in the alfa it gets like 25% packets lost or more! I'm less them 50 feet from my AP, the internal adapter gets 44/70 link quality, and the alfa gets around 60/70 (iwconfig output). Also the system always sets alfa power to 20dbm(100mw), then I have to do sudo iw set reg B0 to make it 30dbm(1000mw), but apparently no significant change. I've installed wireless-compat drivers, no change either. And worst of all, in Windows 7 it works way more smoothly for browsing, though I couldn't test it properly there. I hope its a driver problem, even if it's a pain to find/compile Linux drivers for a starter, I prefer it to a hardware problem where I would need to buy another adapter, since I have no money left (except for the cantenna pieces).

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SQL Operators as text in where clause

- by suggy1982

I have the following table, which is used for storing bandings. The table is maintained via a web frontend. CREATE TABLE [dbo].[Banding]( [BandingID] [int] IDENTITY(1,1) NOT NULL, [ValueLowerLimitOperator] [varchar](10) NULL, [ValueLowerLimit] [decimal](9, 2) NULL, [ValueUpperLimitOperator] [varchar](10) NULL, [ValueUpperLimit] [decimal](9, 2) NULL, [VolumeLowerLimitOperator] [varchar](10) NULL The operator fields store values such as < = <=. I want to get to a position where I can use the operators values stored in the table in a case statement in a where clause. Like this. SELECT * FROM table WHERE CASE ValueLowerLimitOperator WHEN '<' THEN VALUE < X WHEN '>' THEN VALUE > X END rather than having to write mutiple case or if statements for each permutation. Does anyone have any suggestions how I can decode the operators values stored in the table as part of my query and then use them in a case/where statement?

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Having an @ inside of a string - PHP

- by Msencenb

So I know that you use a backslash to escape most things in php however the @ symbol is an operator that suppresses error messages. I'm trying to put an email string like this inside of an array "[email protected]", however php is throwing an error. How do you escape the @ sign? EDIT: Here is the code example that was throwing the error: $arr = array(3=> "[email protected]",4=> "[email protected]"); However replacing the double quotes with single quotes fixes the error as answered below.... why is that true?

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When does ref($variable) return 'IO'?

- by Zaid

Here's the relevant excerpt from the documentation of the ref function: The value returned depends on the type of thing the reference is a reference to. Builtin types include: SCALAR ARRAY HASH CODE REF GLOB LVALUE FORMAT IO VSTRING Regexp Based on this, I imagined that calling ref on a filehandle would return 'IO'. Surprisingly, it doesn't: use strict; use warnings; open my $fileHandle, '<', 'aValidFile'; close $fileHandle; print ref $fileHandle; # prints 'GLOB', not 'IO' perlref tries to explain why: It isn't possible to create a true reference to an IO handle (filehandle or dirhandle) using the backslash operator. The most you can get is a reference to a typeglob, which is actually a complete symbol table entry [...] However, you can still use type globs and globrefs as though they were IO handles. In what circumstances would ref return 'IO' then?

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Need a regular expression for an Irish phone number

- by Eoghan O'Brien

I need to validate an Irish phone number but I don't want to make it too user unfriendly, many people are used to writing there phone number with brackets wrapping their area code followed by 5 to 7 digits for their number, some add spaces between the area code or mobile operator. The format of Irish landline numbers is an area code of between 1 and 4 digits and a number of between 5 to 8 digits. e.g. (021) 9876543 (01)9876543 01 9876543 (0402)39385 I'm looking for a regular expression for Javascript/PHP. Thanks.

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Template type deduction with a non-copyable class

- by Evan Teran

Suppose I have an autolocker class which looks something like this: template <T> class autolocker { public: autolocker(T *l) : lock(l) { lock->lock(); } ~autolocker() { lock->unlock(); } private: autolocker(const autolocker&); autolocker& operator=(const autolocker&); private: T *lock; } Obviously the goal is to be able to use this autolocker with anything that has a lock/unlock method without resorting to virtual functions. Currently, it's simple enough to use like this: autolocker<some_lock_t> lock(&my_lock); // my_lock is of type "some_lock_t" but it is illegal to do: autolocker lock(&my_lock); // this would be ideal Is there anyway to get template type deduction to play nice with this (keep in my autolocker is non-copyable). Or is it just easiest to just specify the type?

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C# : Number Conversion Problem

- by Sayem Ahmed

Today I faced a strange problem in C#. I have an ASP.NET page where user can enter certain price, quantity etc. I get the price value, convert it to double, then multiply it with 100 and then typecast it to an integer. When the price is "33.30", after converting it to double it remains 33.3 (obviously...), but after multiplying it with 100, it becomes 3329.9999999999995, and when I cast it to integer by applying simple cast operator "(int) (price * 100) ", it becomes 3329. Right now I have no idea why this is happening. So I thought may be you guys can help :) .

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Outlook 2007 + Exchange 2010 (Save All Attachments)

- by RobertPitt

About 3 weeks back our company upgraded our mail system to Exchange 2010, all went smooth, few issues but nothing major. A few days ago we had a call from a colleague where he was unable to save all attachments, From File > Save As > Save All Attachments. When the email has a single attachment it works perfectly normal, and depending on the file type it allows you to save multiple attachments. But there's a lot of file types that will not work, such as zip, pdf, doc etc, Usually we get a location box open up asking where we would like to drop the attachments, but it does nothing, You click Save All Attachments and nothing happens. After hours of research I have come across mixed results, a lot of people on forums have been explaining that they have recently crossed over to Exchange 2010 and there issues started there. But on the other hand Microsoft released a KB (278188) which was depressing if that, but that article was published in 2007, as stated by the time stamp, and Exchange 2010 has only come out recently. Im looking to see if you guys have any clues what could be causing this, anything server side that I can take a look at (AD, Exchange, ...). Any help on this is greatly supported

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Winamp has slow /skipping video playback on Windows 7

- by Roy Rico

Hello, I have Windows 7 x64 (7600 90-day trial version) and Winamp 5.6 installed. When I play a video in Windows Media Player, the video plays smooth, however when I play a video in winamp, the video is mostly ok when played back at the original size (but not completely), but if I play it back in fullscreen, the playback gets really slow. The video's audio track plays just fine. I have a DELL XPS 420 computer (8GB of RAM) with a Nvidia GeForce 8800 CTS 512 video card. I've updated to the latest drivers. I have the default Windows 7 codecs, and the CCCP codec pack which used to be all I needed under Windows XP to play all types of videos. Are the codecs needed for Windows Y the same? What's going on? UPDATE: As suggested, I turned off Aero and winamp ran just fine again. So I just have to wait for winamp to be rewritten to work with the way Vista/Windows 7 runs? UPDATE 2: Winamp has updated their player, and it works great with Windows 7 now.

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Pointing to vectors

- by Matt Munson

#include <iostream> #include <vector> using namespace std; int main () { vector <int> qwerty; qwerty.push_back(5); vector <int>* p = &qwerty; cout << p[0]; //error: no match for 'operator<<' in 'std::cout << * p' } I'm generally unclear on how to use pointers with vectors, so I'm pretty mystified as to why this is not working. To my mind, this should print 5 to screen.

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visual studio intellisense error

- by rakkarage

template <typename T> class Test { friend Test<T> & operator * (T lhs, const Test<T> & rhs) { Test<T> r(rhs); // return r *= lhs; } } 4 IntelliSense: identifier "T" is undefined why is T defined on line 3 but not line 4? i mean i guess its not a real error just an intellisense error... it works anyway but is there something wrong? can i fix it? or remove the red squiggles somehow? thanks i am using visual studio 2010... i wonder if this happens in other versions as well?

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DataSet with many OR clauses

- by Silvan

Hello :) I've got a little problem with a query which I create in the Visual Studio Designer. I need a query with a lot of 'OR'-clauses for the same column. I found the operator 'IN', but I don't know how to use that in the Visual Studio Designer: Example IN: SELECT EmployeeID, FirstName, LastName, HireDate, City FROM Employees WHERE City IN ('Seattle', 'Tacoma', 'Redmond') I tried to do it in this way: SELECT [MachineryId], [ConstructionSiteId], [DateTime], [Latitude], [Longitude], [HoursCounter] FROM [PositionData] WHERE [MachineryID] IN @MachineryIDs But this doesn't work. Is there another way to handle a lot of OR clauses? Thank you very much for your help.

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rails - Redirecting console output to a file

- by egarcia

On a bash console, if I do this: cd mydir ls -l > mydir.txt The operator captures the standard input and redirects it to a file; so I get the listing of files in mydir.txt instead of in the standard output. Is there any way to do something similar on the rails console? I've got a ruby statement that generates lots of prints (~8k lines) and I'd like to be able to see it completely, but the console only "remembers" the last 1024 lines or so. So I thought about redirecting to a file - If anyone knows a better option, I'm all ears.

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Consing lists with user-defined type in Haskell

- by user1319603

I have this type I defined myself: data Item = Book String String String Int -- Title, Author, Year, Qty | Movie String String String Int -- Title, Director, Year, Qty | CD String String String Int deriving Show -- Title, Artist, Year, Qty I've created an empty list all_Items = [] With the following function I am trying to insert a new book of type Item (Book) into the all_Items addBook all_Items = do putStrLn "Enter the title of the book" tit <- getLine putStrLn "Enter the author of the book" aut <- getLine putStrLn "Enter the year this book was published" yr <- getLine putStrLn "Enter quantity of copies for this item in the inventory" qty <- getLine Book tit aut yr (read qty::Int):all_Items return(all_Items) I however am receiving this error: Couldn't match expected type `IO a0' with actual type `[a1]' The error points to the line where I am using the consing operator to add the new book to the list. I can gather that it is a type error but I can't figure out what it is that I am doing wrong and how to fix it. Thanks in Advance!

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Best grep-like tool

- by e-satis

I do in file search a lot, and used to love grep. Then I learn the existence of egrep, so I switched to benefit from the advanced regexp. Then I discovered the Eclipse search tool. Much easier to use that grep. Then I found ack : fast, easy, powerful. And now I use grin, which is smooth for pythonistas. I know there is also a couple of this kind of tools with a GUI. So what tool do you use, and why do you think it's the best. Practical features generally are : fast to fire and use; speedy processing; automatically ignore useless files; colored output; output lines, filename, context; allow complex regexp; allow a custom filtering and ouput; GUI + command line intergation; let you open an editor from the result set. There are some related posts on SO : http://stackoverflow.com/questions/87350/what-are-good-grep-tool-for-windows http://stackoverflow.com/questions/981601/colorized-grep-viewing-the-entire-file-with-highlighting http://stackoverflow.com/questions/1028107/is-there-some-unix-util-that-will-allow-me-to-grep-multiple-files-with-little-type http://stackoverflow.com/questions/1027906/unix-find-grep-syntax-vs-awk

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Accessing clearcase view drive from virtual machine is slow

- by PermanentGuest

I have a windows XP virtual machine running under a Windows XP host. On the host : On the host clearcase 7.1.1.2 is installed. I have a dynamic view mapped onto some drive. The view has certain VOB/directory structure where my application DLLs from the nightly build and config files are stored. I run my application on the host machine which uses the DLLs and config files from the VOB and everything runs smooth. Now I want to move this set-up to a virtual machine. On the guest : I'm running the guest with a vm-player. I don't want to install clear-case on this as I don't want to expose this machine onto the network. The network setting in the guest is 'host-only'. I have mapped the host's clearcase view drive as a shared folder and I'm able to access this drive from the virtual machine. Also, the application is running. However, the problem is that the access of the clearcase drive from the virtual machine is very slow. I can experience this from the windows explorer. Due to this, the starting of my application takes several seconds in the virtual machine while on the guest it comes up pretty fast. My question is : Is there any way to speed up the performance? I have managed to copy some of the DLLs which don't change frequently to the virtual machine to improve the performance. However, there are still lot of DLLs which have to be taken from the clearcase drive as they change frequently. VMplayer version is : VM Player 3.0.1 build-227600 Both guest and host is : Windows XP service pack 3 Host clearcase is : clearcase 7.1.1.2

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different explanation

- by Delirium tremens

The following code echoes 5, not 10: $global_obj = null; class my_class { var $value; function my_class() { global $global_obj; $global_obj = &$this; } } $a = new my_class; $a->my_value = 5; $global_obj->my_value = 10; echo $a->my_value; "Upon first examination, it would seem that the constructor of my_class stores a reference to itself inside the $global_obj variable. Therefore, one would expect that, when we later change the value of $global_obj-my_value to 10, the corresponding value in $a would change as well. Unfortunately, the new operator does not return a reference, but a copy of the newly created object." Please, give me a different explanation.

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Permissions in OS X for iTunes library with multiple users

- by John

I currently have a lot of music on an external drive and my iTunes set up from there. However, periodically, when the external drive isn't connected, iTunes will default back to the library location of my home directory user path. I don't want to mess with an external drive, as my Mac's HD is large enough to house the music collection. However, I have 4 family members – all with their own logins – using this same gob of music. I don't want four copies of the library, only one with all libraries referencing it. So, what I want to do is: Move all music files to a shared directory at /Macintosh HD/users/music. I created this directory and adjusted permissions, so all four users can read and write to this directory. Get all four accounts to reference this library instead of the external or local home locations I am hoping I can just check the box to keep library organized in my account, which is the admin and let iTunes move it all. Then delete current libraries for each account and re-add from the new shared location. Will the iTunes organization process cause permissions issues either by setting permissions to all the files access to my account only or write permissions or any other 'gotcha'? I am having a hard time coming up with a smooth solution that won't break everything and cause me to have mega duplicates or access issues. I would prefer not to do any XML library file editing if possible. Am I dreaming?

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How does Hibernate detect dirty state of an entity object?

- by ???'Lenik

Is it using some kind of byte codes modification to the original classes? Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version? I'm having a problem with hashCode() and equals() methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem. If Hibernate won't use hashCode()/equals() to check the dirty state, I guess I should not use equals()/hashCode() for the entity object (not value object), but I'm also afraid if the same operator (==) is not enough. So, the questions are: How does Hibernate know if a property of an object is changed? Do you suggest to override the hashCode()/equals() methods for complicated objects? What if they contains cyclic references? And, also, Would hashCode()/equals() with only the id field be enough?

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SQL vs MySQL: Rules about aggregate operations and GROUP BY

- by Phazyck

In this book I'm currently reading while following a course on databases, the following example of an illegal query using an aggregate operator is given: Find the name and age of the oldest sailor. Consider the following attempt to answer this query: SELECT S.name, S.age FROM Sailors.S The intent is for this query to return not only the maximum age but also the name of the sailors having that age. However, this query is illegal in SQL--if the SELECT clause uses an aggregate operation, then it must use only aggregate operations unless the query contains a GROUP BY clause! Some time later while doing an exercise using MySQL, I faced a similar problem, and made a mistake similar to the one mentioned. However, MySQL didn't complain and just spit out some tables which later turned out not be what I needed. Is the query above really illegal in SQL, but legal in MySQL, and if so, why is that? In what situation would one need to make such a query?

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C++ Urban Myths

- by Neil Butterworth

I'm starting to write an article on what I'm calling "C++ Urban Myths" - that is, ideas and conceptions about C++ that are common but have no actual roots in reality. Some that I've come up with so far are: TR1 is part of standard C++ TR1 (technical Report #1) proposed a whole bunch of changes to C++. Unfortunately, it was never accepted. It is faster to use iterators to access a vector than operator[] Or vice versa. All tests I've carried out indicate the two are nearly identical in performance. The C++ Standard contains something called the STL It doesn't - neither "STL" nor "Standard Template Library" appear in the Standard. I'm wondering if the SO C++ community can come up with any better ones? Ideally, they should be expressible in a single sentence, and not involve any code. Edit: I guess I didn't make it clear enough that I was interested in myths believed by C++ developers, not misconceptions held by non-C++users. Oh well...

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If-statement with logical OR

- by exiter2000

public class Test{ public static void main(String args[]){ int a = 0; int b = 1; int c = 10; if ( a == 0 || b++ == c ){ a = b + c; }else{ b = a + c; } System.out.println("a: " + a + ",b: " + b + ",c: " + c); } } Ok, this is Java code and the output is a: 11,b: 1,c: 10 And I believe the C acts same as Java in this case That is because second condition(b++ == c) would never executed if the first condition is true in 'OR' operator. There is a "NAME" for this. I just don't remember what it is. Does anyone know what this is called?? Thanks in advance

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error: typedef name may not be a nested-name-specifier

- by Autopulated

I am trying to do something along the lines of this answer, and struggling: $ gcc --version gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu4) file.cpp:7: error: template argument 1 is invalid file.cpp:7: error: typedef name may not be a nested-name-specifier And the offending part of the file: template <class R, class C, class T0=void, class T1=void, class T2=void> struct MemberWrap; template <class R, class C, class T0> struct MemberWrap<R, C, T0>{ typedef R (C::*member_t)(T0); typedef typename boost::add_reference<typename T0>::type> TC0; // <---- offending line MemberWrap(member_t f) : m_wrapped(f){ } R operator()(C* p, TC0 p0){ GILRelease guard; return (p->*(this->m_wrapped))(p0); } member_t m_wrapped; };

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