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  • php / phpDoc - @return instance of $this class ?

    - by searbe
    How do I mark a method as "returns an instance of the current class" in my phpDoc? In the following example my IDE (Netbeans) will see that setSomething always returns a foo object. But that's not true if I extent the object - it'll return $this, which in the second example is a bar object not a foo object. class foo { protected $_value = null; /** * Set something * * @param string $value the value * @return foo */ public function setSomething($value) { $this->_value = $value; return $this; } } $foo = new foo(); $out = $foo->setSomething(); So fine - setSomething returns a foo - but in the following example, it returns a bar..: class bar extends foo { public function someOtherMethod(){} } $bar = new bar(); $out = $bar->setSomething(); $out->someOtherMethod(); // <-- Here, Netbeans will think $out // is a foo, so doesn't see this other // method in $out's code-completion ... it'd be great to solve this as for me, code completion is a massive speed-boost. Anyone got a clever trick, or even better, a proper way to document this with phpDoc?

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  • Determining difference in timestamps for two values in the same MySQL table

    - by JayRizzo03
    I am relatively new to programming in PHP, so I apologize if this is a rather simple question. I have a MySQL database table called MachineReports that contains the following values: ReportNum(primary key, auto increment), MachineID and Timestamp Here is some example data: |ReportNum | MachineID | Timestamp | |1 | AD3203 | 2012-11-18 06:32:28| |2 | AD3203 | 2012-11-19 04:00:15| |3 | BC4300 | 2012-11-19 04:00:15| What I am attempting to do is find the difference in timestamps in seconds for each machine ID by iterating over each row set. I am getting stuck on the best way to do this, however. Here is the code I've written so far: <?php include '../dbconnect/dbconnect.php'; $machineID=[]; //Get a list of all MachineIDs in the database foreach($dbh->query('SELECT DISTINCT(MachineID) FROM MachineReports') as $row) { array_push($machineID, $row[0]); } for($i=0;$i<count($machineID);$i++){ foreach($dbh->query("SELECT MachineID FROM MachineReports WHERE MachineID='$machineID[$i]' ORDER BY MachineID") as $row) { //code to associate each machineID with two time stamps goes here } } ? This code just lists out the contents of the table row by row. My ultimate goal is to find the difference in timestamps for a certain MachineID. One of the things I've considered is using a multidimensional array in php - using the $machineID as the key and then storing the timestamp inside the array the key points to. However, I'm uncertain how to do that since my query parses row by row. I have quite a few questions. 1) Is this the most efficient way to be doing this? I suspect my database table design may not be the best. 2)What would be the best way to determine the difference in timestamps for a certain machineID? Even just a pointer to a topic that would prompt me to think about this in a different way would be helpful - I'm not afraid to do research. Thanks!

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  • Resource allocation and automatic deallocation

    - by nabulke
    In my application I got many instances of class CDbaOciNotifier. They all share a pointer to only one instance of class OCIEnv. What I like to achieve is that allocation and deallocation of the resource class OCIEnv will be handled automatically inside class CDbaOciNotifier. The desired behaviour is, with the first instance of class CDbaOciNotifier the environment will be created, after that all following notifiers use that same environment. With the destruction of the last notifier, the environment will be destroyed too (call to custom deleter). What I've got so far (using a static factory method to create notifiers): #pragma once #include <string> #include <memory> #include "boost\noncopyable.hpp" class CDbaOciNotifier : private boost::noncopyable { public: virtual ~CDbaOciNotifier(void); static std::auto_ptr<CDbaOciNotifier> createNotifier(const std::string &tnsName, const std::string &user, const std::string &password); private: CDbaOciNotifier(OCIEnv* envhp); // All notifiers share one environment static OCIEnv* m_ENVHP; // Custom deleter static void freeEnvironment(OCIEnv *env); OCIEnv* m_envhp; }; CPP: #include "DbaOciNotifier.h" using namespace std; OCIEnv* CDbaOciNotifier::m_ENVHP = 0; CDbaOciNotifier::~CDbaOciNotifier(void) { } CDbaOciNotifier::CDbaOciNotifier(OCIEnv* envhp) :m_envhp(envhp) { } void CDbaOciNotifier::freeEnvironment(OCIEnv *env) { OCIHandleFree((dvoid *) env, (ub4) OCI_HTYPE_ENV); *env = null; } auto_ptr<CDbaOciNotifier> CDbaOciNotifier::createNotifier(const string &tnsName, const string &user, const string &password) { if(!m_ENVHP) { OCIEnvCreate( (OCIEnv **) &m_ENVHP, OCI_EVENTS|OCI_OBJECT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *)) 0, (size_t) 0, (dvoid **) 0 ); } //shared_ptr<OCIEnv> spEnvhp(m_ENVHP, freeEnvironment); ...got so far... return auto_ptr<CDbaOciNotifier>(new CDbaOciNotifier(m_ENVHP)); } I'd like to avoid counting references (notifiers) myself, and use something like shared_ptr. Do you see an easy solution to my problem?

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  • Convert one delphi code line to c++

    - by user1332636
    How can I write that line in c++? This is the code in delphi type TSettings = record sFileName: String[50]; siInstallFolder: Byte; bRunFile: Boolean; ... end; .. var i: dword; sZdData: PChar; Settings :Tsettings; begin .... ZeroMemory(@Settings, sizeof(Tsettings)); settings := Tsettings(Pointer(@sZdData[i])^); // this code to c++ c++ code (hope the rest is OK) struct TSettings{ char sFileName[50]; byte siInstallFolder; bool bRunFile; ... } Settings; ... DWORD i; LPBYTE sZdData; ZeroMemory(&Settings, sizeof(TSettings)); Settings = ????? // im failing here i dunno what to do // i need same as in delphi code above

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  • Array length is zero in jQuery.

    - by James123
    I wrote like this. After submit click loop is not excuting. But I saw value are there, But array lenght is showing '0'. (Please see picture). Why it is not going into loop? and $('#myVisibleRows').val(idsString); becoming 'empty'. $(document).ready(function() { $('tr[@class^=RegText]').hide().children('td'); var list_Visible_Ids = []; var idsString, idsArray; alert($('#myVisibleRows').val()); idsString = $('#myVisibleRows').val(); idsArray = idsString.split(','); $.each(idsArray, function() { if (this != "") { $('#' + this).siblings(('.RegText').toggle(true)); window['list_Visible_Ids'][this] = 1; } }); $('tr.subCategory1') .css("cursor", "pointer") .attr("title", "Click to expand/collapse") .click(function() { //this = $(this); $(this).siblings('.RegText').toggle(); list_Visible_Ids[$(this).attr('id')] = $(this).css('display') != 'none' ? 1 : null; alert(list_Visible_Ids[$(this).attr('id')]) }); $('#form1').submit(function() { idsString = ''; $.each(list_Visible_Ids, function(key, val) { alert(val); if (val) { idsString += (idsString != '' ? ',' : '') + key; } }); $('#myVisibleRows').val(idsString); form.submit(); }); });

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  • Internal typedef and circular dependency

    - by bcr
    I have two classes whose functions take typedefed pointers to eachother as return values and parameters. I.e.: class Segment; class Location : public Fwk::NamedInterface { public: // ===== Class Typedefs ===== typedef Fwk::Ptr<Location const> PtrConst; typedef Fwk::Ptr<Location> Ptr; // ===== Class Typedefs End ===== void segmentIs(Segment::Ptr seg); /* ... */ } and class Location; class Segment : public Fwk::NamedInterface { public: // ===== Class Typedefs ===== typedef Fwk::Ptr<Segment const> PtrConst; typedef Fwk::Ptr<Segment> Ptr; // ===== Class Typedefs End ===== void locationIs(Location::Ptr seg); /* ... */ } This understandably generated linker errors...which the forward declarations of the respective classes don't fix. How can I forward declare the Ptr and PtrConst typedefs while keeping these typedefs internal to the class (i.e. I would like to write Location::Ptr to refer to the location pointer type)? Thanks folks!

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  • Parsing string based on initial format

    - by Kayla
    I'm trying to parse a set of lines and extract certain parts of the string based on an initial format (reading a configuration file). A little more explanation: the format can contain up to 4 parts to be formatted. This case, %S will skip the part, %a-%c will extract the part and will be treated as a string, %d as int. What I am trying to do now is to come up with some clever way to parse it. So far I came up with the following prototype. However, my pointer arithmetic still needs some work to skip/extract the parts. Ultimately each part will be stored on an array of structs. Such as: struct st_temp { char *parta; char *partb; char *partc; char *partd; }; ... #include <stdio.h> #include <string.h> #define DIM(x) (sizeof(x)/sizeof(*(x))) void process (const char *fmt, const char *line) { char c; const char *src = fmt; while ((c = *src++) != '\0') { if (c == 'S'); // skip part else if (c == 'a'); // extract %a else if (c == 'b'); // extract %b else if (c == 'c'); // extract %c else if (c == 'd'); // extract %d (int) else { printf("Unknown format\n"); exit(1); } } } static const char *input[] = { "bar 200.1 / / (zaz) - \"bon 10\"", "foo 100.1 / / (baz) - \"apt 20\"", }; int main (void) { const char *fmt = "%S %a / / (%b) - \"%c %d\""; size_t i; for(i = 0; i < DIM (input); i++) { process (fmt, input[i]); } return (0); }

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  • Refetching a previously visited page

    - by user613665
    All, I am having a field day with page refetching. Any help or pointer will be greatly appreciated!! The behavior is a bit specific to mobile browser. Problem: I have two pages and created a shortcut link to pg#1 in the home page. Through a form submit button, user is taken from pg#1 to pg#2. All that is working fine. Now once I am on pg#2. I will leave the browser and click the shortcut later. The browser will stay on pg#2 and won't go to pg#1 even though the path in URLS is different between the two views. It is almost like Django decides that since I have already visited view#1, it doesn't need to fetch it again. This problem or behavior doesn't happen if I move the same code that handle the two views and the templates to a bare bone test project. Setup: I am using django-registration, context session. I am not using any HTML caching tag. I already have DEBUG turned on in my settings.py. Are there other ways that I can tell what the server is doing. Thanks in advance. pdxMobile Update: Here is the code snippets. def sendmsg(request): if request.method =='POST': messages.add_message(request, messages.INFO, "Hello world") return redirect ('rcvmsg') return render_to_response('sendMsg.html',RequestContext(request)) def rcvmsg(request): '''view that receives the msg.''' printMsg ='Didnt get a message' if messages: thisMsg = messages.get_messages(request) for rcvMsg in thisMsg: printMsg = rcvMsg return render_to_response('rcvMsg.html',{'print_msg':printMsg},RequestContext(request)) URL: url(r'^rcvMsg/','mydomain.mainApp.views.rcvmsg',name='rcvmsg'), (r'^sendMsg/code','mydomain.mainApp.views.sendmsg'),

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  • how to pass vector of string to foo(char const *const *const)?

    - by user347208
    Hi, This is my first post so please be nice. I searched in this forum and googled but I still can not find the answer. This problem has bothered me for more than a day, so please give me some help. Thank you. I need to pass a vector of string to a library function foo(char const *const *const). I can not pass the &Vec[0] since it's a pointer to a string. Therefore, I have an array and pass the c_str() to that array. The following is my code (aNames is the vector of string): const char* aR[aNames.size()]; std::transform(aNames.begin(), aNames.end(), aR, boost::bind(&std::string::c_str, _1)); foo(aR); However, it seems it causes some undefined behavior: If I run the above code, then the function foo throw some warnings about illegal characters ('èI' blablabla) in aR. If I print aR before function foo like this: std::copy(aR, aR+rowNames.size(), std::ostream_iterator<const char*>(std::cout, "\n")); foo(aR); Then, everything is fine. My questions are: Does the conversion causes undefined behavior? If so, why? What is the correct way to pass vector of string to foo(char const *const *const)? Thank you very much for your help!

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  • Boost shared_ptr use_count function

    - by photo_tom
    My application problem is the following - I have a large structure foo. Because these are large and for memory management reasons, we do not wish to delete them when processing on the data is complete. We are storing them in std::vector<boost::shared_ptr<foo>>. My question is related to knowing when all processing is complete. First decision is that we do not want any of the other application code to mark a complete flag in the structure because there are multiple execution paths in the program and we cannot predict which one is the last. So in our implementation, once processing is complete, we delete all copies of boost::shared_ptr<foo>> except for the one in the vector. This will drop the reference counter in the shared_ptr to 1. Is it practical to use shared_ptr.use_count() to see if it is equal to 1 to know when all other parts of my app are done with the data. One additional reason I'm asking the question is that the boost documentation on the shared pointer shared_ptr recommends not using "use_count" for production code.

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  • Using unions to simplify casts

    - by Steven Lu
    I realize that what I am trying to do isn't safe. But I am just doing some testing and image processing so my focus here is on speed. Right now this code gives me the corresponding bytes for a 32-bit pixel value type. struct Pixel { unsigned char b,g,r,a; }; I wanted to check if I have a pixel that is under a certain value (e.g. r, g, b <= 0x10). I figured I wanted to just conditional-test the bit-and of the bits of the pixel with 0x00E0E0E0 (I could have wrong endianness here) to get the dark pixels. Rather than using this ugly mess (*((uint32_t*)&pixel)) to get the 32-bit unsigned int value, i figured there should be a way for me to set it up so I can just use pixel.i, while keeping the ability to reference the green byte using pixel.g. Can I do this? This won't work: struct Pixel { unsigned char b,g,r,a; }; union Pixel_u { Pixel p; uint32_t bits; }; I would need to edit my existing code to say pixel.p.g to get the green color byte. Same happens if I do this: union Pixel { unsigned char c[4]; uint32_t bits; }; This would work too but I still need to change everything to index into c, which is a bit ugly but I can make it work with a macro if i really needed to.

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  • Best Approach for Checking and Inserting Records

    - by nevets1219
    In one of our existing C programs which purpose is: Open connection to DB for record in all_record: if record contain certain data: if record is NOT in table A: // see #1 insert record information into table A and B // see #2 Close connection to DB select field from table where field=XXX 2 inserts This is typically done every X months to sync everything up or so I'm told. I've also been told that this process takes roughly a couple of days. There is (currently) at most 2.5million records (though not necessarily all 2.5m will be inserted). One of the table contains 10 fields and the other 5 fields. There isn't much to be done about iterating through the records since that part can't be changed at the moment. What I would like to do is speed up the part where I query MySQL. I'm not sure if I have left out any important details -- please let me know! I'm also no SQL expert so feel free to point out the obvious. I thought about: Putting all the inserts into a transaction (at the moment I'm not sure how important it is for the transaction to be all-or-none or if this affects performance) Using Insert X Where Not Exists Y LOAD DATA INFILE (but that would require I create a (possibly) large temp file) I read that (hopefully someone can confirm) I should drop indexes so they aren't re-calculated. mysql Ver 14.7 Distrib 4.1.22, for sun-solaris2.10 (sparc) using readline 4.3

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  • Array Assignment

    - by Mahesh
    Let me explain with an example - #include <iostream> void foo( int a[2], int b[2] ) // I understand that, compiler doesn't bother about the // array index and converts them to int *a, int *b { a = b ; // At this point, how ever assignment operation is valid. } int main() { int a[] = { 1,2 }; int b[] = { 3,4 }; foo( a, b ); a = b; // Why is this invalid here. return 0; } Is it because, array decays to a pointer when passed to a function foo(..), assignment operation is possible. And in main, is it because they are of type int[] which invalidates the assignment operation. Doesn't a,b in both the cases mean the same ? Thanks. Edit 1: When I do it in a function foo, it's assigning the b's starting element location to a. So, thinking in terms of it, what made the language developers not do the same in main(). Want to know the reason.

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  • I am trying to access the individual bytes in a floating point number and I am getting unexpected results

    - by oweinh
    So I have this so far: #include <iostream> #include <string> #include <typeinfo> using namespace std; int main () { float f = 3.45; // just an example fp# char* ptr = (char*)&f; // a character pointer to the first byte of the fp#? cout << int(ptr[0]) << endl; // these lines are just to see if I get what I cout << int(ptr[1]) << endl; // am looking for... I want ints that I can cout << int(ptr[2]) << endl; // otherwise manipulate. cout << int(ptr[3]) << endl; } the result is: -51 -52 92 64 so obviously -51 and -52 are not in the byte range that I would expect for a char... I have taken information from similar questions to arrive at this code and from all discussions, a conversion from char to int is straightforward. So why negative values? I am trying to look at a four-byte number, therefore I would expect 4 integers, each in the range 0-255. I am using Codeblocks 13.12 with gcc 4.8.1 with option -std=C++11 on a Windows 8.1 device.

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  • In sync query calls, one query causing other query to run slower. Why?

    - by Irchi
    Sorry for the long question, but I think this is an interesting situation and I couldn't find any explanations for it: I was involved in optimization of an application that performed a large number of sequential SELECT and INSERT statements on a single dedicated SQL Server database. The process needs to INSERT a large number of records into a table, but for each of them there should be some value mappings, which performed using SELECT statements on another table in the same database. For a specific execution, it took 90 minutes to run. I used a profiler (JProfiler - the application is Java-based) to determine how much time does each part of the application take. It yields that 60% of the time was spent on INSERT method calls, and almost 20% on SELECT calls (the rest distributed in other parts). After some trials, I came to this situation: I commented out the INSERT query that took 60% of the time. I was expecting for the total run time to be around 35 minutes, as I have removed 60% of the 90 minutes. But the whole process took the same 90 minutes (doing only SELECTs and nothing else), but each SELECT took longer this time! Everything was running sync, there were no async calls. And there was only one single thread of execution. SELECT and INSERT queries are very simple, and don't have anything special, and they are on different tables, but on the same DB. I tested with both the DB on the application machine, and on a remote network machine. I can't think of any explanation for this, as the Profiler (Application profiler, not SQL Profiler) reported the changes in the method call times, and by removing INSERT statements SELECT statements took longer to run. Can anyone give me some kind of explanation of what could have happened? (there can't be cache / query optimization stuff, because the queries were run in sync, and in a single thread, and it was far from affecting the cache this much) I should note that the bottleneck of the speed was in SQL server, using most of the CPU time.

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  • How to delete Drawn Line in java?

    - by Jeyjey
    Hello Folks, well this is my code: import javax.swing.; import javax.; import java.awt.; import java.awt.Color; import java.awt.Graphics.; import java.awt.event.*; import javax.swing.UIManager; public class SimpleGUI extends JFrame{ public SimpleGUI(){ this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) ; } public void go(){ Drawpanel = new Mypanel(); JFrame frame = new JFrame("Chasing Line"); frame.getContentPane().add(BorderLayout.CENTER, Drawpanel); frame.setSize(300,300); frame.setVisible(true); Drawpanel.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() { public void mouseMoved(java.awt.event.MouseEvent evt) { DrawpanelMouseMoved(evt); } }); } public void DrawpanelMouseMoved(java.awt.event.MouseEvent evt) { xpos=evt.getX(); ypos=evt.getY(); System.out.println("Coordinates : X :"+ xpos+"Y: "+ypos); Drawpanel.paintImage(xpos,ypos); } class Mypanel extends JPanel{ public void paintImage(int xpost,int ypost){ Graphics d = getGraphics(); d.setColor(Color.black); d.drawLine(xpost, 0, xpost, this.getHeight()); d.setColor(Color.red); d.drawLine(0, ypost, this.getWidth(),ypost); this.validate(); } } // end the inner class public static void main(String[] args){ try { UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); } catch(Exception e) { System.err.println("Look and feel not set"); } SimpleGUI win = new SimpleGUI(); win.go(); } Mypanel Drawpanel; private int xpos=0; private int ypos=0; } // close SimpleGUI class The problem is how can i delete the old lines?, i mea,make only the current x and y lines appear on the screen, make the intersection between both lines "follow" the mouse pointer. thanks for any reply.

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  • How do I know when to increase or decrease angle to get a specific angle?

    - by Thomas
    Hi. I am programming a game and I have come to a very hard spot. Basically I have a circle and I have 2 angles on this circle. Angle 1 (A) is a point I want angle 2 (B) to go to. During my game every frame I need to check weither or not to increase or decrease my angle value by a certain amount (speed) to eventually reach the first angle. My question is how do I do this? I tried doing this but I don't seem to be doing it right. bool increase = false; float B = [self radiansToDegrees:tankAngle]; float A = [self radiansToDegrees:tankDestinationAngle]; float newAngle = B; if(B < A) { float C = B - (360 - A); float D = A - B; if(C < D) increase = false; else increase = true; } else if(B A) { float C = B - A; float D = A - (360 - B); if(C < D) increase = false; else increase = true; } if(increase) { newAngle += 1.0; } else { newAngle -= 1.0; } if(newAngle 360.0) { newAngle = 0 + (newAngle - 360.0); } else if(newAngle < 0.0) { newAngle = 360 + newAngle; } if(newAngle == 0) newAngle = 360; newAngle = [self degreesToRadians:newAngle]; [self setTanksProperPositionRotation:newAngle]; The basic effect I am trying to achieve is when the user makes a new point, which would be angle 1, angle 2 would move towards angle 1 choosing the fastest direction. I think I have spent around 4 hours trying to figure this out.

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  • Is this an error in "More Effective C++" in Item28?

    - by particle128
    I encountered a question when I was reading the item28 in More Effective C++ .In this item, the author shows to us that we can use member template in SmartPtr such that the SmartPtr<Cassette> can be converted to SmartPtr<MusicProduct>. The following code is not the same as in the book,but has the same effect. #include <iostream> class Base{}; class Derived:public Base{}; template<typename T> class smart{ public: smart(T* ptr):ptr(ptr){} template<typename U> operator smart<U>() { return smart<U>(ptr); } ~smart(){delete ptr;} private: T* ptr; }; void test(const smart<Base>& ) {} int main() { smart<Derived> sd(new Derived); test(sd); return 0; } It indeed can be compiled without compilation error. But when I ran the executable file, I got a core dump. I think that's because the member function of the conversion operator makes a temporary smart, which has a pointer to the same ptr in sd (its type is smart<Derived>). So the delete directive operates twice. What's more, after calling test, we can never use sd any more, since ptr in sd has already been delete. Now my questions are : Is my thought right? Or my code is not the same as the original code in the book? If my thought is right, is there any method to do this? Thanks very much for your help.

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  • optimization math computation (multiplication and summing)

    - by wiso
    Suppose you want to compute the sum of the square of the differences of items: $\sum_{i=1}^{N-1} (x_i - x_{i+1})^2$, the simplest code (the input is std::vector<double> xs, the ouput sum2) is: double sum2 = 0.; double prev = xs[0]; for (vector::const_iterator i = xs.begin() + 1; i != xs.end(); ++i) { sum2 += (prev - (*i)) * (prev - (*i)); // only 1 - with compiler optimization prev = (*i); } I hope that the compiler do the optimization in the comment above. If N is the length of xs you have N-1 multiplications and 2N-3 sums (sums means + or -). Now suppose you know this variable: sum = $x_1^2 + x_N^2 + 2 sum_{i=2}^{N-1} x_i^2$ Expanding the binomial square: $sum_i^{N-1} (x_i-x_{i+1})^2 = sum - 2\sum_{i=1}^{N-1} x_i x_{i+1}$ so the code becomes: double sum2 = 0.; double prev = xs[0]; for (vector::const_iterator i = xs.begin() + 1; i != xs.end(); ++i) { sum2 += (*i) * prev; prev = (*i); } sum2 = -sum2 * 2. + sum; Here I have N multiplications and N-1 additions. In my case N is about 100. Well, compiling with g++ -O2 I got no speed up (I try calling the inlined function 2M times), why?

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  • Which way of declaring a variable is fastest?

    - by ADB
    For a variable used in a function that is called very often and for implementation in J2ME on a blackberry (if that changed something, can you explain)? class X { int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { static int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { public void someFunc(int j) { int i = 0; while( i < j ){ [...] i++; } } } I know there is a difference how a static versus non-static class variable is accessed, but I don't know it would affect the speed. I also remember reading somewhere that in-function variables may be accessed faster, but I don't know why and where I read that. Background on the question: some painting function in games are called excessively often and even small difference in access time can affect the overall performance when a variable is used in a largish loop.

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  • JS best practice for member functions

    - by MickMalone1983
    I'm writing a little mobile games library, and I'm not sure the best practice for declaring member functions of instantiated function objects. For instance, I might create a simple object with one property, and a method to print it: function Foo(id){ this.id = id; this.print = function(){ console.log(this.id); }; }; However, a function which does not need access to 'private' members of the function does not need to be declared in the function at all. I could equally have written: function print(){ console.log(this.id); }; function Foo(id){ this.id = id; this.print = print; }; When the function is invoked through an instance of Foo, the instance becomes the context for this, so the output is the same in either case. I'm not entirely sure how memory is allocated with JS, and I can't find anything that I can understand about something this specific, but it seems to me that with the first example all members of Foo, including the print function, are duplicated each time it is instantiated - but with the second, it just gets a pointer to one, pre-declared function, which would save any more memory having to be allocated as more instances of Foo are created. Am I correct, and if I am, is there any memory/performance benefit to doing this?

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  • Conceptual data modeling: Is RDF the right tool? Other solutions?

    - by paprika
    I'm planning a system that combines various data sources and lets users do simple queries on these. A part of the system needs to act as an abstraction layer that knows all connected data sources: the user shouldn't [need to] know about the underlying data "providers". A data provider could be anything: a relational DBMS, a bug tracking system, ..., a weather station. They are hooked up to the query system through a common API that defines how to "offer" data. The type of queries a certain data provider understands is given by its "offer" (e.g. I know these entities, I can give you aggregates of type X for relationship Y, ...). My concern right now is the unification of the data: the various data providers need to agree on a common vocabulary (e.g. the name of the entity "customer" could vary across different systems). Thus, defining a high level representation of the entities and their relationships is required. So far I have the following requirements: I need to be able to define objects and their properties/attributes. Further, arbitrary relations between these objects need to be represented: a verb that defines the nature of the relation (e.g. "knows"), the multiplicity (e.g. 1:n) and the direction/navigability of the relation. It occurs to me that RDF is a viable option, but is it "the right tool" for this job? What other solutions/frameworks do exist for semantic data modeling that have a machine readable representation and why are they better suited for this task? I'm grateful for every opinion and pointer to helpful resources.

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  • Processor, OS : 32bit, 64 bit

    - by Sandbox
    I am new to programming and come from a non-CS background (no formal degree). I mostly program winforms using C#. I am confused about 32 bit and 64 bit.... I mean, have heard about 32 bit OS, 32 bit processor and based on which a program can have maximum memory. How it affects the speed of a program. There are lot more questions which keep coming to mind. I tried to go through some Computer Organization and Architecture books. But, either I am too dumb to understand what is written in there or the writers assume that the reader has some CS background. Can someone explain me these things in a plain simple English or point me to something which does that. EDIT: I have read things like In 32-bit mode, they can access up to 4GB memory; in 64-bit mode, they can access much much more....I want to know WHY to all such things. BOUNTY: Answers below are really good....esp one by Martin. But, I am looking at a thorough explanation, but in plain simple English.

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  • How can a B-tree node be represented?

    - by chronodekar
    We're learning B-trees in class and have been asked to implement them in code. The teacher has left choice of programming language to us and I want to try and do it in C#. My problem is that the following structure is illegal in C#, unsafe struct BtreeNode { int key_num; // The number of keys in a node int[] key; // Array of keys bool leaf; // Is it a leaf node or not? BtreeNode*[] c; // Pointers to next nodes } Specifically, one is not allowed to create a pointer to point to the structure itself. Is there some work-around or alternate approach I could use? I'm fairly certain that there MUST be a way to do this within the managed code, but I can't figure it out. EDIT: Eric's answer pointed me in the right direction. Here's what I ended up using, class BtreeNode { public List<BtreeNode> children; // The child nodes public static int MinDeg; // The Minimum Degree of the tree public bool IsLeaf { get; set; } // Is the current node a leaf or not? public List<int> key; // The list of keys ... }

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  • [C++] Parent-Child scheme

    - by rubenvb
    I'm writing a class that holds a pointer to a parent object of the same type (think Qt's QObject system). Each object has one parent, and the parent should not be destroyed when a child is destroyed (obviously). class MyClass { public: MyClass(const MyClass* ptr_parent): parent(parent){}; ~MyClass(){ delete[] a_children; }; private: const MyClass* ptr_parent; // go to MyClass above MyClass* a_children; // go to MyClass below size_t sz_numChildren; // for iterating over a_children } (Excuse my inline coding, it's only for brevity) Will destroying the "Master MyClass" take care of all children? No child should be able to kill it's parent, because I would then have pointers in my main program to destroyed objects, correct? Why might you ask? I need a way to "iterate" through all subdirectories and find all files on a platform independent level. The creation of this tree will be handled by native API's, the rest won't. Is this a good idea to start with? Thanks!

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