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• COM-Objects containing maps / content error(0)

  - by Florian Berzsenyi

  I'm writing a small wrapper to get familiar with some important topics in C++ (WinAPI, COM, STL,OOP). For now, my class shall be able to create a (child) window. Mainly, this window is connected to a global message loop that distribute messages to a local loop of the right instance (global is static, local is virtual). Obviously, there are surely better ways to do that but I'm using std::maps to store HWND and their instance pointer in pairs (the Global loop looks for the pointer with the HWND-parameter, gets itself the pointer from the map and calls then the local loop). Now, it appears that the map does not accept any values because of a unknown reason. It seems to allocate enough space but something went wrong anyway [ (error) 0 is displayed instead of the entries in visual C++). I've looked that up in google as well and found out that maps cause some trouble when used in classes AND DLLs. May this be the reason and is there any solution?? Protected scope of class: static std::map<HWND,MAP_BASE_OBJECT*> m_LoopBuf Implementation in .cpp-file: std::map<HWND,MAP_BASE_OBJECT*> HWindow::m_LoopBuf;

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• Deserialize complex JSON (VB.NET)

  - by Ssstefan

  I'm trying to deserialize json returned by some directions API similar to Google Maps API. My JSON is as follows (I'm using VB.NET 2008): jsontext = { "version":0.3, "status":0, "route_summary": { "total_distance":300, "total_time":14, "start_point":"43", "end_point":"42" }, "route_geometry":[[51.025421,18.647631],[51.026131,18.6471],[51.027802,18.645639]], "route_instructions": [["Head northwest on 43",88,0,4,"88 m","NW",334.8],["Continue on 42",212,1,10,"0.2 km","NW",331.1,"C",356.3]] } So far I came up with the following code: Dim js As New System.Web.Script.Serialization.JavaScriptSerializer Dim lstTextAreas As Output_CloudMade() = js.Deserialize(Of Output_CloudMade())(jsontext) I'm not sure how to define complex class, i.e. Output_CloudMade. I'm trying something like: Public Class RouteSummary Private mTotalDist As Long Private mTotalTime As Long Private mStartPoint As String Private mEndPoint As String Public Property TotalDist() As Long Get Return mTotalDist End Get Set(ByVal value As Long) mTotalDist = value End Set End Property Public Property TotalTime() As Long Get Return mTotalTime End Get Set(ByVal value As Long) mTotalTime = value End Set End Property Public Property StartPoint() As String Get Return mStartPoint End Get Set(ByVal value As String) mStartPoint = value End Set End Property Public Property EndPoint() As String Get Return mEndPoint End Get Set(ByVal value As String) mEndPoint = value End Set End Property End Class Public Class Output_CloudMade Private mVersion As Double Private mStatus As Long Private mRSummary As RouteSummary 'Private mRGeometry As RouteGeometry 'Private mRInstructions As RouteInstructions Public Property Version() As Double Get Return mVersion End Get Set(ByVal value As Double) mVersion = value End Set End Property Public Property Status() As Long Get Return mStatus End Get Set(ByVal value As Long) mStatus = value End Set End Property Public Property Summary() As RouteSummary Get Return mRSummary End Get Set(ByVal value As RouteSummary) mRSummary = value End Set End Property 'Public Property Geometry() As String ' Get ' End Get ' Set(ByVal value As String) ' End Set 'End Property 'Public Property Instructions() As String ' Get ' End Get ' Set(ByVal value As String) ' End Set 'End Property End Class but it does not work. The problem is with complex properties, like route_summary. It is filled with "nothing". Other properties, like "status" or "version" are filled properly. Any ideas, how to define class for the above JSON? Can you share some working code for deserializing JSON in VB.NET? Thanks,

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• accumulator don't compile

  - by Abruzzo Forte e Gentile

  HI All I am using boost accumulators. These 2 lines use to work fine with current version of boost in LInux. accumulator_set< double, stats< tag::covariance<double, tag::covariate1> > > acc_cov; accumulator_set< double, stats< tag::variance > > acc_var; When I moved to a Sun machine where it is installed boost v1.40 I have this building error "/opt/boost/boost/accumulators/framework/depends_on.hpp", line 276: Error:<no tag> cannot be initialized in a constructor. "/opt/boost/boost/fusion/container/list/cons.hpp", line 85: Where: While instantiating "boost::accumulators::detail::accumulator_wrapper<int, int>::accumulator_wrapper(const boost::accumulators::detail::accumulator_wrapper<int, int>&)". "/opt/boost/boost/fusion/container/list/cons.hpp", line 85: Where: Instantiated from non-template code. 1 Error(s) Do you know how can I fix those errors and why I have this issue? Thanks AFG

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• Dynamic memory inside a struct

  - by Maximilien

  Hello, I'm editing a piece of code, that is part of a big project, that uses "const's" to initialize a bunch of arrays. Because I want to parametrize these const's I have to adapt the code to use "malloc" in order to allocate the memory. Unfortunately there is a problem with structs: I'm not able to allocate dynamic memory in the struct itself. Doing it outside would cause to much modification of the original code. Here's a small example: int globalx,globaly; struct bigStruct{ struct subStruct{ double info1; double info2; bool valid; }; double data; //subStruct bar[globalx][globaly]; subStruct ** bar=(subStruct**)malloc(globalx*sizeof(subStruct*)); for(int i=0;i<globalx;i++) bar[i]=(*subStruct)malloc(globaly*sizeof(subStruct)); }; int main(){ globalx=2; globaly=3; bigStruct foo; for(int i=0;i<globalx;i++) for(int j=0;j<globaly;j++){ foo.bar[i][j].info1=i+j; foo.bar[i][j].info2=i*j; foo.bar[i][j].valid=(i==j); } return 0; } Note: in the program code I'm editing globalx and globaly were const's in a specified namespace. Now I removed the "const" so they can act as parameters that are set exactly once. Summarized: How can I properly allocate memory for the substruct inside the struct? Thank you very much! Max

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• Inner angle between two lines

  - by ocell

  Hi folks, I have two lines: Line1 and Line2. Each line is defined by two points (P1L1(x1, y1), P2L1(x2, y2) and P1L1(x1, y1), P2L3(x2, y3)). I want to know the inner angle defined by these two lines. For do it I calculate the angle of each line with the abscissa: double theta1 = atan(m1) * (180.0 / PI); double theta2 = atan(m2) * (180.0 / PI); After to know the angle I calculate the following: double angle = abs(theta2 - theta1); The problem or doubt that I have is: sometimes I get the correct angle but sometimes I get the complementary angle (for me outer). How can I know when subtract 180º to know the inner angle? There is any algorithm better to do that? Because I tried some methods: dot product, following formula: result = (m1 - m2) / (1.0 + (m1 * m2)); But always I have the same problem; I never known when I have the outer angle or the inner angle! Thanks in advance for reading my trouble and for your time! Oscar.

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• Defining an implementation independent version of the global object in JavaScript

  - by Aadit M Shah

  I'm trying to define the global object in JavaScript in a single line as follows: var global = this.global || this; The above statement is in the global scope. Hence in browsers the this pointer is an alias for the window object. Assuming that it's the first line of JavaScript to be executed in the context of the current web page, the value of global will always be the same as that of the this pointer or the window object. In CommonJS implementations, such as RingoJS and node.js the this pointer points to the current ModuleScope. However, we can access the global object through the property global defined on the ModuleScope. Hence we can access it via the this.global property. Hence this code snippet works in all browsers and in at least RingoJS and node.js, but I have not tested other CommomJS implementations. Thus I would like to know if this code will not yield correct results when run on any other CommonJS implementation, and if so how I may fix it. Eventually, I intend to use it in a lambda expression for my implementation independent JavaScript framework as follows (idea from jQuery): (function (global) { // javascript framework })(this.global || this);

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• Qt/C++, Problems with large QImage

  - by David Günzel

  I'm pretty new to C++/Qt and I'm trying to create an application with Visual Studio C++ and Qt (4.8.3). The application displays images using a QGraphicsView, I need to change the images at pixel level. The basic code is (simplified): QImage* img = new QImage(img_width,img_height,QImage::Format_RGB32); while(do_some_stuff) { img->setPixel(x,y,color); } QGraphicsPixmapItem* pm = new QGraphicsPixmapItem(QPixmap::fromImage(*img)); QGraphicsScene* sc = new QGraphicsScene; sc->setSceneRect(0,0,img->width(),img->height()); sc->addItem(pm); ui.graphicsView->setScene(sc); This works well for images up to around 12000x6000 pixel. The weird thing happens beyond this size. When I set img_width=16000 and img_height=8000, for example, the line img = new QImage(...) returns a null image. The image data should be around 512,000,000 bytes, so it shouldn't be too large, even on a 32 bit system. Also, my machine (Win 7 64bit, 8 GB RAM) should be capable of holding the data. I've also tried this version: uchar* imgbuf = (uchar*) malloc(img_width*img_height*4); QImage* img = new QImage(imgbuf,img_width,img_height,QImage::Format_RGB32); At first, this works. The img pointer is valid and calling img-width() for example returns the correct image width (instead of 0, in case the image pointer is null). But as soon as I call img-setPixel(), the pointer becomes null and img-width() returns 0. So what am I doing wrong? Or is there a better way of modifying large images on pixel level? Regards, David

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• Escaping colons in hibernate createSQLQuery

  - by Stratosgear

  I am confused on how I can create an SQL statement containing colons. I am trying to create a view and I am using (notice the double colons): create view MyView as ( SELECT tableA.colA as colA, tableB.colB as colB, round(tableB.colD / 1024)::numeric, 2) as calcValue, FROM tableA, tableB WHERE tableA.colC = 'someValue' ); This is a postgres query and I am forced to use the double colons (::) in order to correctly run the statement. I then pass the above statement through: s.createSQLQuery(myQuery).executeUpdate(); and I get a: Exception in thread "main" org.hibernate.exception.DataException: \ could not execute native bulk manipulation query at org.hibernate.exception.SQLStateConverter.convert(\ SQLStateConverter.java:102) ... more stacktrace... with an output of my above statement changed as (notice the question mark): create view MyView as ( SELECT tableA.colA as colA, tableB.colB as colB, round(tableB.colD / 1024)?, 2) as calcValue, FROM tableA, tableB WHERE tableA.colC = 'someValue' ); Obviously, hibernate confuses my colons with named parameters. Is there a way to escape the colons (a google suggestion that mentions that a single colon is escaped as a double colon does NOT work) or another way of running this statement? Thanks.

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• Pear HTML BBcode Hyperlink

  - by rrrfusco

  Has anyone used the PEAR HTML BBcode Package? I don't really understand why hyperlink target _blank does not open a new tab in firefox. INSERT Snippet [url=http://site.com t=_blank]Link[/url] PHP Require PEAR require_once 'HTML/BBCodeParser.php'; $options = @parse_ini_file('BBCodeParser.ini'); $parser = new HTML_BBCodeParser($options); $parser->setText($text); $parser->parse(); echo $parser->getParsed(); BBCodeParser.ini [HTML_BBCodeParser] ; http://articles.sitepoint.com/article/bb-code-php-application/ ; possible values: single|double ; use single or double quotes for attributes quotestyle = double ; possible values: all|nothing|strings ; quote all attribute values, none, or only the strings quotewhat = all ; the opening tag character open = "[" ; the closing tag character close = "]" ; possible values: true|false ; use xml style closing tags for single html tags (<img> or <img />) xmlclose = true ; possible values: a comma seperated list of filters ; comma seperated list of filters to use filters = Basic,Extended,Links,Images,Lists ; filters = Basic,Extended,Links,Images,Lists,Email,MyBB

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• Common lisp, CFFI, and instantiating c structs

  - by andrew

  Hi, I've been on google for about, oh, 3 hours looking for a solution to this "problem." I'm trying to figure out how to instantiate a C structure in lisp using CFFI. I have a struct in c: struct cpVect{cpFloat x,y;} Simple right? I have auto-generated CFFI bindings (swig, I think) to this struct: (cffi:defcstruct #.(chipmunk-lispify "cpVect" 'classname) (#.(chipmunk-lispify "x" 'slotname) :double) (#.(chipmunk-lispify "y" 'slotname) :double)) This generates a struct "VECT" with slots :X and :Y, which foreign-slot-names confirms (please note that I neither generated the bindings or programmed the C library (chipmunk physics), but the actual functions are being called from lisp just fine). I've searched far and wide, and maybe I've seen it 100 times and glossed over it, but I cannot figure out how to create a instance of cpVect in lisp to use in other functions. Note the function: cpShape *cpPolyShapeNew(cpBody *body, int numVerts, cpVect *verts, cpVect offset) Takes not only a cpVect, but also a pointer to a set of cpVects, which brings me to my second question: how do I create a pointer to a set of structs? I've been to http://common-lisp.net/project/cffi/manual/html_node/defcstruct.html and tried the code, but get "Error: Unbound variable: PTR" (I'm in Clozure CL), not to mention that looks to only return a pointer, not an instance. I'm new to lisp, been going pretty strong so far, but this is the first real problem I've hit that I can't figure out. Thanks!

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• C# vs C - Big performance difference

  - by John

  I'm finding massive performance differences between similar code in C anc C#. The C code is: #include <stdio.h> #include <time.h> #include <math.h> main() { int i; double root; clock_t start = clock(); for (i = 0 ; i <= 100000000; i++){ root = sqrt(i); } printf("Time elapsed: %f\n", ((double)clock() - start) / CLOCKS_PER_SEC); } And the C# (console app) is: using System; using System.Collections.Generic; using System.Text; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { DateTime startTime = DateTime.Now; double root; for (int i = 0; i <= 100000000; i++) { root = Math.Sqrt(i); } TimeSpan runTime = DateTime.Now - startTime; Console.WriteLine("Time elapsed: " + Convert.ToString(runTime.TotalMilliseconds/1000)); } } } With the above code, the C# completes in 0.328125 seconds (release version) and the C takes 11.14 seconds to run. The c is being compiled to a windows executable using mingw. I've always been under the assumption that C/C++ were faster or at least comparable to C#.net. What exactly is causing the C to run over 30 times slower? EDIT: It does appear that the C# optimizer was removing the root as it wasn't being used. I changed the root assignment to root += and printed out the total at the end. I've also compiled the C using cl.exe with the /O2 flag set for max speed. The results are now: 3.75 seconds for the C 2.61 seconds for the C# The C is still taking longer, but this is acceptable

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• Intellisense on custom types in Iron Python

  - by Anish Patel

  Hi everybody, I'm just starting to play around with IronPython and am having a hard time using it with custom types created in C#. I can get IronPython to load in assemblies from C# classes, but I'm struggling without the help of intellisense. If I have a class in C# as defined below, how can I make it so that IronPython will be able to see the methods/properties that are available in it? public class Person { public string Name { get; set; } public int Age{ get; set; } public double Weight{ get; set; } public double Height { get; set; } public double CalculateBMI() { return Weight/Math.Pow(Height, 2); } } In Iron python I'd instance a Person object as follows: newPerson = Person() newPerson.Name = 'John' newPerson.Age = 25 newPerson.Weight = 75 newPerson.Height = 1.70 newPerson.CalculateBMI() The thing that is annoying me is that I want to be able to say newPerson = Person() And then be able to see all the methods and properties associated with the person object whenever I type: newPerson. Anyone have any ideas if this can be done?

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• Best way to get a single value from a DataTable?

  - by PiersMyers

  I have a number of static classes that contain tables like this: using System; using System.Data; using System.Globalization; public static class TableFoo { private static readonly DataTable ItemTable; static TableFoo() { ItemTable = new DataTable("TableFoo") { Locale = CultureInfo.InvariantCulture }; ItemTable.Columns.Add("Id", typeof(int)); ItemTable.Columns["Id"].Unique = true; ItemTable.Columns.Add("Description", typeof(string)); ItemTable.Columns.Add("Data1", typeof(int)); ItemTable.Columns.Add("Data2", typeof(double)); ItemTable.Rows.Add(0, "Item 1", 1, 1.0); ItemTable.Rows.Add(1, "Item 2", 1, 1.0); ItemTable.Rows.Add(2, "Item 3", 2, 0.75); ItemTable.Rows.Add(3, "Item 4", 4, 0.25); ItemTable.Rows.Add(4, "Item 5", 1, 1.0); } public static DataTable GetItemTable() { return ItemTable; } public static int Data1(int id) { DataRow[] dr = ItemTable.Select("Id = " + id); if (dr.Length == 0) { throw new ArgumentOutOfRangeException("id", "Out of range."); } return (int)dr[0]["Data1"]; } public static double Data2(int id) { DataRow[] dr = ItemTable.Select("Id = " + id); if (dr.Length == 0) { throw new ArgumentOutOfRangeException("id", "Out of range."); } return (double)dr[0]["Data2"]; } } Is there a better way of writing the Data1 or Data2 methods that return a single value from a single row that matches the given id?

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• Suppressing PostSharp Multicast with Attribute

  - by Dan Bryant

  I've recently started experimenting with PostSharp and I found a particularly helpful aspect to automate implementation of INotifyPropertyChanged. You can see the example here. The basic functionality is excellent (all properties will be notified), but there are cases where I might want to suppress notification. For instance, I might know that a particular property is set once in the constructor and will never change again. As such, there is no need to emit the code for NotifyPropertyChanged. The overhead is minimal when classes are not frequently instantiated and I can prevent the problem by switching from an automatically generated property to a field-backed property and writing to the field. However, as I'm learning this new tool, it would be helpful to know if there is a way to tag a property with an attribute to suppress the code generation. I'd like to be able to do something like this: [NotifyPropertyChanged] public class MyClass { public double SomeValue { get; set; } public double ModifiedValue { get; private set; } [SuppressNotify] public double OnlySetOnce { get; private set; } public MyClass() { OnlySetOnce = 1.0; } }

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• How do I update a progress bar in Cocoa during a long running loop?

  - by Nic

  Hi, I've got a while loop, that runs for many seconds and that's why I want to update a progress bar (NSProgressIndicator) during that process, but it updates only once after the loop has finished. The same happens if I want to update a label text, by the way. I believe, my loop prevents other things of that application to happen. There must be another technique. Does this have to do with threads or something? Am I on the right track? Can someone please give me a simple example, how to “optimize” my application? My application is a Cocoa Application (Xcode 3.2.1) with these two methods in my Example_AppDelegate.m: // This method runs when a start button is clicked. - (IBAction)startIt:(id)sender { [progressbar setDoubleValue:0.0]; [progressbar startAnimation:sender]; running = YES; // this is a instance variable int i = 0; while (running) { if (i++ = processAmount) { // processAmount is something like 1000000 running = NO; continue; } // Update progress bar double progr = (double)i / (double)processAmount; NSLog(@"progr: %f", progr); // Logs values between 0.0 and 1.0 [progressbar setDoubleValue:progr]; [progressbar needsDisplay]; // Do I need this? // Do some more hard work here... } } // This method runs when a stop button is clicked, but as long // as -startIt is busy, a click on the stop button does nothing. - (IBAction)stopIt:(id)sender { NSLog(@"Stop it!"); running = NO; [progressbar stopAnimation:sender]; } I'm really new to Objective-C, Cocoa and applications with a UI. Thank you very much for any helpful answer.

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• Filling an Area in visual studio C#

  - by lajoo

  I'm drawing a circle in C# and i have divided it into some parts,i want to fill different parts with different colors,is there anyway to do this? and how?i tried using fillpie() but i couldn't get the arguments to work. here is the code: int r = 150; g.DrawEllipse(Pens.Black, 300 - r, 250 - r, 2 * r, 2 * r); if (p != 0) g.DrawLine(Pens.Black, 300, 250, 300 + r, 250); double sum; sum = 0.0; for (int j = 0; j < p; j++) sum += data[j].value; double angle; angle = 0.0; for (int i = 0; i < p; i++) { angle += (double)(data[i].value / sum) * 2.0 * Math.PI; textBox1.Text += sum.ToString() + " : " + angle.ToString() + ":" + Math.Cos(angle).ToString() + "\r\n"; g.DrawLine(Pens.Black, 300, 250, 300 + (int)(Math.Cos(angle) * r), 250 - (int)(Math.Sin(angle) * r)); //g.FillPie(Brushes.Black, 300-r , 250 - r, r, r ,(float)(angle),(float)(angle+ (data[i].value / sum) * 2.0 * Math.PI)); } this actually divides the circle into different parts,i don't know how to fill them the commented line is where i

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• Stored procedure using cursor in mySql.

  - by RAVI

  I wrote a stored procedure using cursor in mysql but that procedure is taking 10 second to fetch the result while that result set have only 450 records so, I want to know that why that proedure is taking that much time to fetch tha record. procedure as below: DELIMITER // DROP PROCEDURE IF EXISTS curdemo123// CREATE PROCEDURE curdemo123(IN Branchcode int,IN vYear int,IN vMonth int) BEGIN DECLARE EndOfData,tempamount INT DEFAULT 0; DECLARE tempagent_code,tempplantype,tempsaledate CHAR(12); DECLARE tempspot_rate DOUBLE; DECLARE var1,totalrow INT DEFAULT 1; DECLARE cur1 CURSOR FOR select SQL_CALC_FOUND_ROWS ad.agentCode,ad.planType,ad.amount,ad.date from adplan_detailstbl ad where ad.branchCode=Branchcode and (ad.date between '2009-12-1' and '2009-12-31')order by ad.NUM_ID asc; DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET EndOfData = 1; DROP TEMPORARY TABLE IF EXISTS temptable; CREATE TEMPORARY TABLE temptable (agent_code varchar(15), plan_type char(12),sale double,spot_rate double default '0.0', dATE DATE); OPEN cur1; SET totalrow=FOUND_ROWS(); while var1 <= totalrow DO fetch cur1 into tempagent_code,tempplantype,tempamount,tempsaledate; IF((tempplantype='Unit Plan' OR tempplantype='MIP') OR tempplantype='STUP') then select spotRate into tempspot_rate from spot_amount where ((monthCode=vMonth and year=vYear) and ((agentCode=tempagent_code and branchCode=Branchcode) and (planType=tempplantype))); INSERT INTO temptable VALUES(tempagent_code,tempplantype,tempamount,tempspot_rate,tempsaledate); else INSERT INTO temptable(agent_code,plan_type,sale,dATE) VALUES(tempagent_code,tempplantype,tempamount,tempsaledate); END IF; SET var1=var1+1; END WHILE; CLOSE cur1; select * from temptable; DROP TABLE temptable; END // DELIMITER ;

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• The Implications of Modern Day Software Development Abstractions

  - by Andreas Grech

  I am currently doing a dissertation about the implications or dangers that today's software development practices or teachings may have on the long term effects of programming. Just to make it clear: I am not attacking the use abstractions in programming. Every programmer knows that abstractions are the bases for modularity. What I want to investigate with this dissertation are the positive and negative effects abstractions can have in software development. As regards the positive, I am sure that I can find many sources that can confirm this. But what about the negative effects of abstractions? Do you have any stories to share that talk about when certain abstractions failed on you? The main concern is that many programmers today are programming against abstractions without having the faintest idea of what the abstraction is doing under-the-covers. This may very well lead to bugs and bad design. So, in you're opinion, how important is it that programmers actually know what is going below the abstractions? Taking a simple example from Joel's Back to Basics, C's strcat: void strcat( char* dest, char* src ) { while (*dest) dest++; while (*dest++ = *src++); } The above function hosts the issue that if you are doing string concatenation, the function is always starting from the beginning of the dest pointer to find the null terminator character, whereas if you write the function as follows, you will return a pointer to where the concatenated string is, which in turn allows you to pass this new pointer to the concatenation function as the *dest parameter: char* mystrcat( char* dest, char* src ) { while (*dest) dest++; while (*dest++ = *src++); return --dest; } Now this is obviously a very simple as regards abstractions, but it is the same concept I shall be investigating. Finally, what do you think about the issue that schools are preferring to teach Java instead of C and Lisp ? Can you please give your opinions and your says as regards this subject? Thank you for your time and I appreciate every comment.

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• RBG to CbyCr conversion code

  - by user1446688

  I am wondering why this code does not work. Basically it is supposed to convert between RGB and CbYCr. When I convert from RGB to CbYCr then back to RGB I do not get the original RGB values. What is wrong with this code? #define MIN(a,b) (((a)<(b))?(a):(b)) #define MAX(a,b) (((a)(b))?(a):(b)) struct _rgb { int R; int G; int B; }; typedef struct _rgb rgb; struct _cbycr { int Cb; int Y; int Cr; }; typedef struct _cbycr cbycr; void cbycr2rgb(rgb *c, double Y, double Cb, double Cr) { int r = (int)(Y + 1.40200 * (Cr - 0x80)); int g = (int)(Y - 0.34414 * (Cb - 0x80) - 0.71414 * (Cr - 0x80)); int b = (int)(Y + 1.77200 * (Cb - 0x80)); c->R = MAX(0, MIN(255, r)); c->G = MAX(0, MIN(255, g)); c->B = MAX(0, MIN(255, b)); } void rgb2cbycr(cbycr *c, int R, int G, int B) { c->Y = (int)(0.299 * R + 0.587 * G + 0.114 * B); c->Cb = (int)(-0.16874 * R - 0.33126 * G + 0.50000 * B); c->Cr =(int)(0.50000 * R - 0.41869 * G - 0.08131 * B); } int main() { cbycr _cbycr; rgb _rgb; _rgb.R = 50; _rgb.G = 50; _rgb.B = 50; rgb2cbycr(&_cbycr, _rgb.R, _rgb.G, _rgb.B); cbycr2rgb(&_rgb, _cbycr.Y, _cbycr.Cb, _cbycr.Cr); printf("rgb=%d %d %d\n", _rgb.R, _rgb.G, _rgb.B); return 0; } output: rgb=0 185 0

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• Atomic swap in GNU C++

  - by Steve

  I want to verify that my understanding is correct. This kind of thing is tricky so I'm almost sure I am missing something. I have a program consisting of a real-time thread and a non-real-time thread. I want the non-RT thread to be able to swap a pointer to memory that is used by the RT thread. From the docs, my understanding is that this can be accomplished in g++ with: // global Data *rt_data; Data *swap_data(Data *new_data) { #ifdef __GNUC__ // Atomic pointer swap. Data *old_d = __sync_lock_test_and_set(&rt_data, new_data); #else // Non-atomic, cross your fingers. Data *old_d = rt_data; rt_data = new_data; #endif return old_d; } This is the only place in the program (other than initial setup) where rt_data is modified. When rt_data is used in the real-time context, it is copied to a local pointer. For old_d, later on when it is sure that the old memory is not used, it will be freed in the non-RT thread. Is this correct? Do I need volatile anywhere? Are there other synchronization primitives I should be calling? By the way I am doing this in C++, although I'm interested in whether the answer differs for C. Thanks ahead of time.

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• Some optimization about the code (computing ranks of a vector)?

  - by user1748356

  The following code is a function (performance-critical) to compute tied ranks of a vector: mergeSort(x,inds,ci); //a sort function to sort vector x of length ci, also returns keys (inds) of x. int tj=0; double xi=x[0]; for (int j = 1; j < ci; ++j) { if (x[j] > xi) { double rankvalue = 0.5 * (j - 1 + tj); for (int k = tj; k < j; ++k) { ranks[inds[k]]=rankvalue; }; tj = j; xi = x[j]; }; }; double rankvalue = 0.5 * (ci - 1 + tj); for (int k = tj; k < ci; ++k) { ranks[inds[k]]=rankvalue; }; The problem is, the supposed performance bottleneck mergeSort(), which is O(NlogN) is several times faster than the other part of codes (which is O(N)), which suggests there is room for huge improvment with the other part of the codes, any advices?

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• What is the purpose of the s==NULL case for mbrtowc?

  - by R..

  mbrtowc is specified to handle a NULL pointer for the s (multibyte character pointer) argument as follows: If s is a null pointer, the mbrtowc() function shall be equivalent to the call: mbrtowc(NULL, "", 1, ps) In this case, the values of the arguments pwc and n are ignored. As far as I can tell, this usage is largely useless. If ps is not storing any partially-converted character, the call will simply return 0 with no side effects. If ps is storing a partially-converted character, then since '\0' is not valid as the next byte in a multibyte sequence ('\0' can only be a string terminator), the call will return (size_t)-1 with errno==EILSEQ. and leave ps in an undefined state. The intended usage seems to have been to reset the state variable, particularly when NULL is passed for ps and the internal state has been used, analogous to mbtowc's behavior with stateful encodings, but this is not specified anywhere as far as I can tell, and it conflicts with the semantics for mbrtowc's storage of partially-converted characters (if mbrtowc were to reset state when encountering a 0 byte after a potentially-valid initial subsequence, it would be unable to detect this dangerous invalid sequence). If mbrtowc were specified to reset the state variable only when s is NULL, but not when it points to a 0 byte, a desirable state-reset behavior would be possible, but such behavior would violate the standard as written. Is this a defect in the standard? As far as I can tell, there is absolutely no way to reset the internal state (used when ps is NULL) once an illegal sequence has been encountered, and thus no correct program can use mbrtowc with ps==NULL.

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• How best to calculate derived currency rate conversions using C#/LINQ?

  - by chillitom

  class FxRate { string Base { get; set; } string Target { get; set; } double Rate { get; set; } } private IList<FxRate> rates = new List<FxRate> { new FxRate {Base = "EUR", Target = "USD", Rate = 1.3668}, new FxRate {Base = "GBP", Target = "USD", Rate = 1.5039}, new FxRate {Base = "USD", Target = "CHF", Rate = 1.0694}, new FxRate {Base = "CHF", Target = "SEK", Rate = 8.12} // ... }; Given a large yet incomplete list of exchange rates where all currencies appear at least once (either as a target or base currency): What algorithm would I use to be able to derive rates for exchanges that aren't directly listed? I'm looking for a general purpose algorithm of the form: public double Rate(string baseCode, string targetCode, double currency) { return ... } In the example above a derived rate would be GBP-CHF or EUR-SEK (which would require using the conversions for EUR-USD, USD-CHF, CHF-SEK) Whilst I know how to do the conversions by hand I'm looking for a tidy way (perhaps using LINQ) to perform these derived conversions perhaps involving multiple currency hops, what's the nicest way to go about this?

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• C standard addressing simplification inconsistency

  - by Chris Lutz

  Section §6.5.3.2 "Address and indirection operators" ¶3 says (relevant section only): The unary & operator returns the address of its operand. ... If the operand is the result of a unary * operator, neither that operator nor the & operator is evaluated and the result is as if both were omitted, except that the constraints on the operators still apply and the result is not an lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor the unary * that is implied by the [] is evaluated and the result is as if the & operator were removed and the [] operator were changed to a + operator. ... This means that this: int *i = NULL; printf("%p", (void *) (&*i) ); printf("%p", (void *) (&i[10]) ); Should be perfectly legal, printing the null pointer (probably 0) and the null pointer plus 10 (probably 10). The standard seems very clear that both of those cases are required to be optimized. However, it doesn't seem to require the following to be optimized: struct { int a; short b; } *s = 0; printf("%p", (void *) (&s->b) ); This seems awfully inconsistent. I can see no reason that the above code shouldn't print the null pointer plus sizeof(int) (possibly 4). Simplifying a &-> expression is going to be the same conceptually (IMHO) as &[], a simple address-plus-offset. It's even an offset that's going to be determinable at compile time, rather than potentially runtime with the [] operator. Is there anything in the rationale about why this is so seemingly inconsistent?

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• How best to deal with warning c4305 when type could change?

  - by identitycrisisuk

  I'm using both Ogre and NxOgre, which both have a Real typedef that is either float or double depending on a compiler flag. This has resulted in most of our compiler warnings now being: warning C4305: 'argument' : truncation from 'double' to 'Ogre::Real' When initialising variables with 0.1 for example. Normally I would use 0.1f but then if you change the compiler flag to double precision then you would get the reverse warning. I guess it's probably best to pick one and stick with it but I'd like to write these in a way that would work for either configuration if possible. One fix would be to use #pragma warning (disable : 4305) in files where it occurs, I don't know if there are any other more complex problems that can be hidden by not having this warning. I understand I would push and pop these in header files too so that they don't end up spreading across code. Another is to create some macro based on the accuracy compiler flag like: #if OGRE_DOUBLE_PRECISION #define INIT_REAL(x) (x) #else #define INIT_REAL(x) static_cast<float>( x ) #endif which would require changing all the variable initialisation done so far but at least it would be future proof. Any preferences or something I haven't thought of?

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