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  • Will an optimizing compiler remove calls to a method whose result will be multiplied by zero?

    - by Tim R.
    Suppose you have a computationally expensive method, Compute(p), which returns some float, and another method, Falloff(p), which returns another float from zero to one. If you compute Falloff(p) * Compute(p), will Compute(p) still run when Falloff(p) returns zero? Or would you need to write a special case to prevent Compute(p) from running unnecessarily? Theoretically, an optimizing compiler could determine that omitting Compute when Falloff returns zero would have no effect on the program. However, this is kind of hard to test, since if you have Compute output some debug data to determine whether it is running, the compiler would know not to omit it because of that debug info, resulting in sort of a Schrodinger's cat situation. I know the safe solution to this problem is just to add the special case, but I'm just curious.

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  • Java Persistence: Cast to something the result of Query.getResultList() ?

    - by GuiSim
    Hey everyone, I'm new to persistence / hibernate and I need your help. Here's the situation. I have a table that contains some stuff. Let's call them Persons. I'd like to get all the entries from the database that are in that table. I have a Person class that is a simple POJO with a property for each column in the table (name, age,..) Here's what I have : Query lQuery = myEntityManager.createQuery("from Person") List<Person> personList = lQuery.getResultList(); However, I get a warning saying that this is an unchecked conversion from List to List<Person> I thought that simply changing the code to Query lQuery = myEntityManager.createQuery("from Person") List<Person> personList = (List<Person>)lQuery.getResultList(); would work.. but it doesn't. Is there a way to do this ? Does persistence allow me to set the return type of the query ? (Through generics maybe ? )

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  • How can I use one stream and save result to many places?

    - by plasticrabbit
    I using servlet and Apache ServletFileUpload that provides stream to uploaded image. All I want to do is to store that image to db and also store resized (I using JAI) version to db. How can I achieve this without saving image to drive. As I understand stream can be read only once. So I need to store whole image in memory? Is it expensive for performance? Or there are another way?

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  • What is the result of "new int[ 0 ]"? [closed]

    - by ArunSaha
    Possible Duplicates: What does zero-sized array allocation do/mean? C++ new int[0] — will it allocate memory? int * p; p = new int[ 0 ]; What is the expected outcome when new is called for zero number of elements? Is the outcome defined or undefined? Further, is it okay to call delete [] p; on that pointer? What is the intuition/analogy to this situation of pointer to an array of zero elements? Thanks in advance. Regards, Arun

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  • Can I use a static var to "cache" the result? C++

    - by flyout
    I am using a function that returns a char*, and right now I am getting the compiler warning "returning address of local variable or temporary", so I guess I will have to use a static var for the return, my question is can I make something like if(var already set) return var else do function and return var? This is my function: char * GetUID() { TCHAR buf[20]; StringCchPrintf(buf, 20*sizeof(char), TEXT("%s"), someFunction()); return buf; } And this is what I want to do: char * GetUID() { static TCHAR buf[20]; if(strlen(buf)!=0) return buf; StringCchPrintf(buf, 20*sizeof(char), TEXT("%s"), someFunction()); return buf; } Is this a well use of static vars? And should I use ZeroMemory(&buf, 20*sizeof(char))? I removed it because if I use it above the if(strlen...) my TCHAR length is never 0, should I use it below?

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  • Javascript match part of url, if statement based on result.

    - by nick
    Here is an example of the url i'm trying to match: http://store.mywebsite.com/folder-1/folder-2/item3423434.aspx What im trying to match is http: //store.mywebsite.com/folder-1 except that "folder-1" will always be a different value. I can't figure out how to write an if statement for this: Example (pseudo-code) if(url contains http://store.mywebsite.com/folder-1) do this else if (url contains http://store.mywebsite.com/folder-2) do something else etc

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  • Return cell reference as result of if statement with vlookups.

    - by EMJ
    I have two sets of data in excel. One contains a set of data which represents the initial step of a process. The other set of data represents the additional steps which take place after the first step is completed. Each of the data records in the "additional step data" has an id in a column. I need to find the identifying codes of the "additional step data" which correspond with the initial step data records. The problem is that I have to match the data in 4 columns between the two data sets and return the id of the "additional step data". I started by doing a combination of an if and vlookup functions, but I got stuck when I tried to figure out how to get the if statement to reference the id of the matching "additional step data". Basically I am trying to avoid having to search by manually filtering between two sets of data and finding corresponding records. Does anyone have any idea about how to do this?

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  • Method returns an IDisposable - Should I dispose of the result, even if it's not assigned to anythin

    - by mjd79
    This seems like a fairly straightforward question, but I couldn't find this particular use-case after some searching around. Suppose I have a simple method that, say, determines if a file is opened by some process. I can do this (not 100% correctly, but fairly well) with this: public bool IsOpen(string fileName) { try { File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None); } catch { // if an exception is thrown, the file must be opened by some other process return true; } } (obviously this isn't the best or even correct way to determine this - File.Open throws a number of different exceptions, all with different meanings, but it works for this example) Now the File.Open call returns a FileStream, and FileStream implements IDisposable. Normally we'd want to wrap the usage of any FileStream instantiations in a using block to make sure they're disposed of properly. But what happens in the case where we don't actually assign the return value to anything? Is it still necessary to dispose of the FileStream, like so: try { using (File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None)); { /* nop */ } } catch { return true; } Should I create a FileStream instance and dispose of that? try { using (FileStream fs = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None)); } ... Or are these totally unnecessary? Can we simply call File.Open and not assign it to anything (first code example), and let the GC dispose of it right away?

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  • MySQL only returning one result. Im Baffled.

    - by Tapha
    Here is te code: <?php //Starting session session_start(); //Includes mass includes containing all the files needed to execute the full script //Also shows homepage elements without customs require_once ('includes/mass.php'); $username = $_SESSION['username']; if (isset($username)) { //Query database for the users networths $sq_l = "SELECT * FROM user"; $sql_query_worth = mysql_query($sq_l); while ($row = mysql_fetch_assoc($sql_query_worth)) { $dbusername = $row['username']; } echo $dbusername; } ?>

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  • Is there any way to view PHP code (the actual code not the compiled result) from a client machine?

    - by Columbo
    This may be a really stupid question...I started worrying last night that there might be someway to view PHP files on a server via a browser or someother means on a client machine. My worry is, I have an include file that contains the database username and password. If there were a way to put the address of this file in to a browser or some other system and see the code itself then it would be an issue for obvious reasons. Is this a legitimate concern? If so how do people go about preventing this?

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  • Do I need to cast the result of strtol to int?

    - by Kristo
    The following code does not give a warning with g++ 4.1.1 and -Wall. int octalStrToInt(const std::string& s) { return strtol(s.c_str(), 0, 8); } I was expecting a warning because strtol returns a long int but my function is only returning a plain int. Might other compilers emit a warning here? Should I cast the return value to int in this case as a good practice?

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  • Can nohup change the result of a C++ code?

    - by Biga
    I am having this very weird behaviour with a C++ code: It gives me different results when running with and without 'nohup' (reproducible in cygwin and linux). I mean, if I get the same executable and run it like './run' or run it like 'nohup ./run out.log', I get different results! I use std::cout to output to screen, all lines ending with endl; I use ifstream for the input file; I use ofstream for output, all lines ending with endl. I am using g++ 4. Any idea what is going on?

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  • memcached: which is faster, doing an add (and checking result), or doing a get (and set when returni

    - by Mike Sherov
    The title of this question isn't so clear, but the code and question is straightforward. Let's say I want to show my users an ad once per day. To accomplish this, every time they visit a page on my site, I check to see if a certain memcache key has any data stored on it. If so, don't show an ad. If not, store the value '1' in that key with an expiration of 86400. I can do this 2 ways: //version a $key='OPD_'.date('Ymd').'_'.$type.'_'.$user; if($memcache->get($key)===false){ $memcache->set($key,'1',false,$expire); //show ad } //version b $key='OPD_'.date('Ymd').'_'.$type.'_'.$user; if($memcache->add($key,'1',false,$expire)){ //show ad } Now, it might seem obvious that b is better, it always makes 1 memcache call. However, what is the overhead of "add" vs. "get"? These aren't the real comparisons... and I just made up these numbers, but let's say 1 add ~= 1 set ~= 5 get in terms of effort, and the average user views 5 pages a day: a: (5 get * 1 effort) + (1 set * 5 effort) = 10 units of effort b: (5 add * 5 effort) = 25 units of effort Would it make sense to always do the add call? Is this an unnecessary micro-optimization?

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  • Does @import in CSS result in additional http requests?

    - by Mo Boho
    I have an ecommerce site that has about 8 CSS files linked from the header - resulting in 8 separate http requests to the server. I consolidated all the CSS files into 1 big one, resulting in a 67kb (!) file - to cut down the http requests to 1 for our css files. I'm finding this size a CSS file a little unmanageable in light of the fact I'm performing updates on the site constantly. My concern is my users may catch me in the middle of updating and see a NON-styled page when moving from page to page - b/c 67kb still takes a good 2-3 seconds before it is successfully placed on the remote server via FTP. My question is: does the use of @import within this large CSS file to break up the files into smaller more manageable sizes (within that CSS file) take us back to the original 8 http-requests when the pages is loaded? Or are @imports in CSS handle differently somehow?

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  • Why does cloning the django inline formsets result to forms with similar ids and names?

    - by user1289167
    In my project I use django inline formsets. I got the jquery to clone the formsets but unfortunately the cloned forms have the same names and ids and so data entered in the last one overwrites the data from the first form. What could I be doing wrong? Here is the script: <script type="text/javascript">> function cloneMore(selector, type) { var newElement = $(selector).clone(true); var total = $('#id_' + type + '-TOTAL_FORMS').val(); newElement.find(':input').each(function() { var name = $(this).attr('name').replace('-' + (total-1) + '-','-' + total + '-'); var id = 'id_' + name; $(this).attr({'name': name, 'id': id}).val('').removeAttr('checked'); }); newElement.find('label').each(function() { var newFor = $(this).attr('for').replace('-' + (total-1) + '-','-' + total + '-'); $(this).attr('for', newFor); }); total++; $('#id_' + type + '-TOTAL_FORMS').val(total); $(selector).after(newElement); } </script>

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  • Java reflection Method invocations yield result faster than Fields?

    - by omerkudat
    I was microbenchmarking some code (please be nice) and came across this puzzle: when reading a field using reflection, invoking the getter Method is faster than reading the Field. Simple test class: private static final class Foo { public Foo(double val) { this.val = val; } public double getVal() { return val; } public final double val; // only public for demo purposes } We have two reflections: Method m = Foo.class.getDeclaredMethod("getVal", null); Field f = Foo.class.getDeclaredField("val"); Now I call the two reflections in a loop, invoke on the Method, and get on the Field. A first run is done to warm up the VM, a second run is done with 10M iterations. The Method invocation is consistently 30% faster, but why? Note that getDeclaredMethod and getDeclaredField are not called in the loop. They are called once and executed on the same object in the loop. I also tried some minor variations: made the field non-final, transitive, non-public, etc. All of these combinations resulted in statistically similar performance. Edit: This is on WinXP, Intel Core2 Duo, Sun JavaSE build 1.6.0_16-b01, running under jUnit4 and Eclipse.

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  • MySql paging; "Showing result-set" of "total found" help

    - by Camran
    I need a formula for showing results on my classifieds website. I am now done with the paging of records, but this formula for showing results remains. I want it like this: Showing 1-50 of 123 found. Now what is the formula for this? I have these variables which should be enough I think: $results_per_page = 50; //results per page $page = 1; //current page Also a variable called $num_total contains the total nr of hits, in this case 123. Thanks

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  • Unable to generate a temporary class (result=1). error CS0030: Cannot convert type 'Type[]' to 'Type'?

    - by grady
    I get this error after I created a class from my xsd file using the xsd.exe tool. So I searched the net and found a solution. Here is the link: http://satov.blogspot.com/2006/12/xsdexe-generated-classes-causing.html Problem is that this makes the code run, but somehow the deserialized data seems corrupt. I did what the site suggests and in the end the 2nd array dimension is always empty (see the comments of the site, somebody also had this problem). Question is, how do I solve this issue now? Is there another tool to create the xsd file? I tried Xsd2Code, without success. Thanks :-)

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  • How can I update a column in a table with the result of a select statement that uses row being updat

    - by Sailing Judo
    This SQL statement example is very close to what I think I need... update table1 set value1 = x.value1 from (select value1, code from table2 where code = something) as x However, what I need to do is change the "something" in the above example to a value from the row that is being updated. For example, I tried this but it didn't work: update table1 A set value1 = x.value1 from (select value1, code from table2 where code = A.something) as x This is a one time operation to update an existing table and I'm not really looking for high performance way to do this. Any solution that gets the task done is good enough.

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  • Why does `Array(0,1,2) == Array(0,1,2)` not return the expected result?

    - by soc
    As far as I understand, Scala's == defines the natural equality of two objects. I expected that Array(0,1,2) == Array(0,1,2) compares the natural equality e. g. checks if all elements of the array return true when compared with the corresponding elements of the other array. People told me that Scala's Array is just a Java [] which only compares identity. But Scala's String is also just a Java String but Scala overrides equals to compare natural equality. I wonder why Array's equals method was not overridden, too. Thank you for your thoughts!

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