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• C++ Boolean problem (comparison between two arrays)

  - by Martin

  Hello! I have a problem to do. I already did some part of it, however I stuck and don't know exactly what to do next. The question: " You are given two arrays of ints, named A and B. One contains AMAXELEMENTS and the other contains BMAXELEMENTS. Write a Boolean-valued function that returns true if there is at least one point in A that is the same as a point in B, and false if there is no match between two arrays. " The two arrays are made up by me, I think if I know how to compare two arrays I will be fine, and I will be able to finish my problem. This is what I have so far (I changed AMAXELEMENTS to AMAX, and BMAXELEMENTS to BMAX): #include <iostream> using namespace std; int main(){ const int AMAX=5, BMAX=6; int i; bool c1=true,c2=false; int A[AMAX]={2,4,1,5,9}; int B[BMAX]={9,12,32,43,23,11}; for(i=0;i<BMAX;i++) if (B[i]==A[i]) // <---- I think this part has to look different, but I can't figure it out. cout<<c1<<endl; else cout<< c2<<endl; return 0; }

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• How to make ActiveRecord work with legacy partitioned/sharded databases/tables?

  - by Utensil

  thanks for your time first...after all the searching on google, github and here, and got more confused about the big words(partition/shard/fedorate),I figure that I have to describe the specific problem I met and ask around. My company's databases deals with massive users and orders, so we split databases and tables in various ways, some are described below: way database and table name shard by (maybe it's should be called partitioned by?) YZ.X db_YZ.tb_X order serial number last three digits YYYYMMDD. db_YYYYMMDD.tb date YYYYMM.DD db_YYYYMM.tb_ DD date too The basic concept is that databases and tables are seperated acording to a field(not nessissarily the primary key), and there are too many databases and too many tables, so that writing or magically generate one database.yml config for each database and one model for each table isn't possible or at least not the best solution. I looked into drnic's magic solutions, and datafabric, and even the source code of active record, maybe I could use ERB to generate database.yml and do database connection in around filter, and maybe I could use named_scope to dynamically decide the table name for find, but update/create opertions are bounded to "self.class.quoted_table_name" so that I couldn't easily get my problem solved. And even I could generate one model for each table, because its amount is up to 30 most. But this is just not DRY! What I need is a clean solution like the following DSL: class Order < ActiveRecord::Base shard_by :order_serialno do |key| [get_db_config_by(key), #because some or all of the databaes might share the same machine in a regular way or can be configed by a hash of regex, and it can also be a const get_db_name_by(key), get_tb_name_by(key), ] end end Can anybody enlight me? Any help would be greatly appreciated~~~~

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• iPhone - Using sql database - insert statement failing

  - by Satyam svv

  Hi, I'm using sqlite database in my iphone app. I've a table which has 3 integer columns. I'm using following code to write to that database table. -(BOOL)insertTestResult { NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString* documentsDirectory = [paths objectAtIndex:0]; NSString* dataBasePath = [documentsDirectory stringByAppendingPathComponent:@"test21.sqlite3"]; BOOL success = NO; sqlite3* database = 0; if(sqlite3_open([dataBasePath UTF8String], &database) == SQLITE_OK) { BOOL res = (insertResultStatement == nil) ? createStatement(insertResult, &insertResultStatement, database) : YES; if(res) { int i = 1; sqlite3_bind_int(insertResultStatement, 0, i); sqlite3_bind_int(insertResultStatement, 1, i); sqlite3_bind_int(insertResultStatement, 2, i); int err = sqlite3_step(insertResultStatement); if(SQLITE_ERROR == err) { NSAssert1(0, @"Error while inserting Result. '%s'", sqlite3_errmsg(database)); success = NO; } else { success = YES; } sqlite3_finalize(insertResultStatement); insertResultStatement = nil; } } sqlite3_close(database); return success;} The command sqlite3_step is always giving err as 19. I'm not able to understand where's the issue. Tables are created using following queries: CREATE TABLE [Patient] (PID integer NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,PFirstName text NOT NULL,PLastName text,PSex text NOT NULL,PDOB text NOT NULL,PEducation text NOT NULL,PHandedness text,PType text) CREATE TABLE PatientResult(PID INTEGER,PFreeScore INTEGER NOT NULL,PForcedScore INTEGER NOT NULL,FOREIGN KEY (PID) REFERENCES Patient(PID)) I've only one entry in Patient table with PID = 1 BOOL createStatement(const char* query, sqlite3_stmt** stmt, sqlite3* database){ BOOL res = (sqlite3_prepare_v2(database, query, -1, stmt, NULL) == SQLITE_OK); if(!res) NSLog( @"Error while creating %s => '%s'", query, sqlite3_errmsg(database)); return res;}

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• Reflection and Generics get value of property

  - by GigaPr

  Hi i am trying to implement a generic method which allows to output csv file public static void WriteToCsv<T>(List<T> list) where T : new() { const string attachment = "attachment; filename=PersonList.csv"; HttpContext.Current.Response.Clear(); HttpContext.Current.Response.ClearHeaders(); HttpContext.Current.Response.ClearContent(); HttpContext.Current.Response.AddHeader("content-disposition", attachment); HttpContext.Current.Response.ContentType = "text/csv"; HttpContext.Current.Response.AddHeader("Pragma", "public"); bool isFirstRow = true; foreach (T item in list) { //Get public properties PropertyInfo[] propertyInfo = item.GetType().GetProperties(); while (isFirstRow) { WriteColumnName(propertyInfo); isFirstRow = false; } Type type = typeof (T); StringBuilder stringBuilder = new StringBuilder(); foreach (PropertyInfo info in propertyInfo) { //string value ???? I am trying to get the value of the property info for the item object } HttpContext.Current.Response.Write(stringBuilder.ToString()); HttpContext.Current.Response.Write(Environment.NewLine); } HttpContext.Current.Response.End(); } but I am not able to get the value of the object's property Any suggestion? Thanks

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• how to write binary copy of structure array to file

  - by cerr

  I would like to write a binary image of a structure array to a binary file. I have tried this so far: #include <stdio.h> #include <string.h> #define NUM 256 const char *fname="binary.bin"; typedef struct foo_s { int intA; int intB; char string[20]; }foo_t; void main (void) { foo_t bar[NUM]; bar[0].intA = 10; bar[0].intB = 999; strcpy(bar[0].string,"Hello World!"); Save(bar); printf("%s written succesfully!\n",fname); } int Save(foo_t* pData) { FILE *pFile; int ptr = 0; int itr = 0; pFile = fopen(fname, "w"); if (pFile == NULL) { printf("couldn't open %s\n", fname); return; } for (itr = 0; itr<NUM; itr++) { for (ptr=0; ptr<sizeof(foo_t); ptr++) { fputc((unsigned char)*((&pData[itr])+ptr), pFile); } fclose(pFile); } } but the compiler is saying aggregate value used where an integer was expected fputc((unsigned char)*((&pData[itr])+ptr), pFile); and I don't quite understand why, what am I doing wrong? Thanks!

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• SQLite DB open time really long Problem

  - by sxingfeng

  I am using sqlite in c++ windows, And I have a db size about 60M, When I open the sqlite db, It takes about 13 second. sqlite3* mpDB; nRet = sqlite3_open16(szFile, &mpDB); And if I closed my application and reopen it again. It takse only less then 1 second. First, I thought It is because of disk cache. So I preload the 60M db file before sqlite open, and read the file using CFile, However, after preloading, the first time is still very slow. BOOL CQFilePro::PreLoad(const CString& strPath) { boost::shared_array<BYTE> temp = boost::shared_array<BYTE>(new BYTE[PRE_LOAD_BUFFER_LENGTH]); int nReadLength; try { CFile file; if (file.Open(strPath, CFile::modeRead) == FALSE) { return FALSE; } do { nReadLength = file.Read(temp.get(), PRE_LOAD_BUFFER_LENGTH); } while (nReadLength == PRE_LOAD_BUFFER_LENGTH); file.Close(); } catch(...) { } return TRUE; } My question is what is the difference between first open and second open. How can I accelerate the sqlite open-process.

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• Creating a process in ASP.NET MVC controller

  - by GRKamath

  I have a requirement to run an application through my MVC controller. To get the installation path I used following link (I used answer provided by Fredrik Mörk). It worked and I could able to run the exe through a process. The problem occurred when I deployed this solution on IIS where it did not create the process as it was creating in local dev environment. Can anybody tell me how to create a windows process through a solution which is hosted on IIS ? private string GetPathForExe(string fileName) { private const string keyBase = @"SOFTWARE\Wow6432Node\MyApplication"; RegistryKey localMachine = Registry.LocalMachine; RegistryKey fileKey = localMachine.OpenSubKey(string.Format(@"{0}\{1}", keyBase, fileName)); object result = null; if (fileKey != null) { result = fileKey.GetValue("InstallPath"); } fileKey.Close(); return (string)result; } public void StartMyApplication() { Process[] pname = Process.GetProcessesByName("MyApplication"); if (pname.Length == 0) { string appDirectory = GetPathForExe("MyApplication"); Directory.SetCurrentDirectory(appDirectory); ProcessStartInfo procStartInfo = new ProcessStartInfo("MyApplication.exe"); procStartInfo.WindowStyle = ProcessWindowStyle.Hidden; Process proc = new Process(); proc.StartInfo = procStartInfo; proc.Start(); } }

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• Problems with variadic function (C)

  - by morpheous

  I have the following function from some legacy code that I am maintaining. long getMaxStart(long start, long count, const myStruct *s1, ...) { long i1, maxstart; myStruct *s2; va_list marker; maxstart = start; /*BUGFIX: 003 */ /*(va_start(marker, count);*/ va_start(marker, s1); for (i1 = 1; i1 <= count; i1++) { s2 = va_arg(marker, myStruct *); /* <- s2 is assigned null here */ maxstart = MAX(maxstart, s2->firstvalid); /* <- SEGV here */ } va_end(marker); return (maxstart); } When the function is called with only one myStruct argument, it causes a SEGV. The code compiled and run without crashing on an XP, when I compiled it using VS2005. I have now moved the code to Ubuntu Karmic and I am having problems with the stricter compiler on Linux. Is anyone able to spot what is causing the parameter not to be read correctly in the var_arg() statement? I am compiling using gcc version 4.4.1

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• Using boost::iterator_adaptor

  - by Neil G

  I wrote a sparse vector class (see #1, #2.) I would like to provide two kinds of iterators: The first set, the regular iterators, can point any element, whether set or unset. If they are read from, they return either the set value or value_type(), if they are written to, they create the element and return the lvalue reference. Thus, they are: Random Access Traversal Iterator and Readable and Writable Iterator The second set, the sparse iterators, iterate over only the set elements. Since they don't need to lazily create elements that are written to, they are: Random Access Traversal Iterator and Readable and Writable and Lvalue Iterator I also need const versions of both, which are not writable. I can fill in the blanks, but not sure how to use boost::iterator_adaptor to start out. Here's what I have so far: class iterator : public boost::iterator_adaptor< iterator // Derived , value_type* // Base , boost::use_default // Value , boost::?????? // CategoryOrTraversal > class sparse_iterator : public boost::iterator_adaptor< iterator // Derived , value_type* // Base , boost::use_default // Value , boost::random_access_traversal_tag? // CategoryOrTraversal >

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• Declaring an enum within a class

  - by bporter

  In the following code snippet, the Color enum is declared within the Car class in order to limit the scope of the enum and to try not to "pollute" the global namespace. class Car { public: enum Color { RED, BLUE, WHITE }; void SetColor( Car::Color color ) { _color = color; } Car::Color GetColor() const { return _color; } private: Car::Color _color; }; (1) Is this a good way to limit the scope of the Color enum? Or, should I declare it outside of the Car class, but possibly within its own namespace or struct? I just came across this article today, which advocates the latter and discusses some nice points about enums: http://gamesfromwithin.com/stupid-c-tricks-2-better-enums. (2) In this example, when working within the class, is it best to code the enum as Car::Color, or would just Color suffice? (I assume the former is better, just in case there is another Color enum declared in the global namespace. That way, at least, we are explicit about the enum to we are referring.) Thanks in advance for any input on this.

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• How can I tell when the Text of a System.Windows.Forms.GroupBox wraps to the next line?

  - by fre0n

  I'm creating a GroupBox at runtime and setting its Text property. Usually, the text is only on one line, but sometimes it wraps. The problem is that the controls contained in the GroupBox cover up the GroupBox's text. What I'd like to do is determine if and when the text wraps. Specifically, I'd like to determine how much extra height the wrapped text takes up as compared to a single line. That way, I can reposition the GroupBox's controls and adjust its height. Initially, I thought I'd do this by calling the GroupBox's CreateGraphics() method, and using the Graphics to measure the string. Something like this: private void SetGroupBoxText(GroupBox grp, string text) { const int somePadding = 10; Graphics g = grp.CreateGraphics(); SizeF textSize = g.MeasureString(text, grp.Font); if (textSize.Width > (grp.Width - somePadding)) { // Adjust height, etc. } } The problem is that the size generated by g.MeasureString(text, grp.Font) doesn't seem to be accurate. I determined that it wasn't accurate by putting enough of a single character to cause a wrap, then measuring the resulting string. For example, it took 86 pipes (|) to until a wrap happened. When I measured that string, its width was ~253. And it took 16 capital W's to force a wrap - its string had a width of ~164. These were the two extremes that I tested. My GroupBox's width was 189. (a's took 29 and had a width of ~180, O's took 22 and had a width of ~189) Does anyone have any ideas? (hacks, WinAPI, etc. are welcome solutions)

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• SQLITE crash when no data present in table

  - by johnblack45

  Hey, Im having a problem with my app that causes it to crash when no data is present in the table when using a table view. I have tested my code and it works fine as long as there is data present but i need it to work when there is no data present. -(void)initialiseTableData { NSMutableArray *array = [[NSMutableArray alloc]init]; sqlite3 *db = [iCaddyAppDelegate getNewDBConnection]; sqlite3_stmt *statement; const char *sql = "select courseId, courseName, totalPar, totalyardage, holePars, holeYardages, holeStrokeIndexs from Course"; if(sqlite3_prepare_v2(db, sql, -1, &statement, NULL)!= SQLITE_OK) { NSAssert1(0,@"Error preparing statement",sqlite3_errmsg(db)); sqlite3_close(db); } else { while (sqlite3_step(statement) == SQLITE_ROW) { Course *temp = [[Course alloc]init]; temp.courseId = sqlite3_column_int(statement,0); temp.courseName = [NSString stringWithFormat:@"%s",(char*)sqlite3_column_text(statement,1)]; temp.totalPar =sqlite3_column_int(statement,2); temp.totalYardage =sqlite3_column_int(statement,3); NSString tempHolePars = [NSString stringWithFormat:@"%s",(char)sqlite3_column_text(statement,4)]; NSString tempHoleYardages = [NSString stringWithFormat:@"%s",(char)sqlite3_column_text(statement,5)]; NSString tempHoleStrokeIndexes = [NSString stringWithFormat:@"%s",(char)sqlite3_column_text(statement,6)]; NSArray *temp1 = [tempHolePars componentsSeparatedByString:@":"]; NSArray *temp2 = [tempHoleYardages componentsSeparatedByString:@":"]; NSArray *temp3 = [tempHoleStrokeIndexes componentsSeparatedByString:@":"]; for(int i = 0; i<=17; i++) { NSString *temp1String = [temp1 objectAtIndex:i]; [temp.holePars insertObject:temp1String atIndex:i]; NSString *temp2String = [temp2 objectAtIndex:i]; [temp.holeYardages insertObject:temp2String atIndex:i]; NSString *temp3String = [temp3 objectAtIndex:i]; [temp.holeStrokeIndexes insertObject:temp3String atIndex:i]; } [array addObject:temp]; } self.list = array; [self.table reloadData]; } }

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• Templates, Function Pointers and C++0x

  - by user328543

  One of my personal experiments to understand some of the C++0x features: I'm trying to pass a function pointer to a template function to execute. Eventually the execution is supposed to happen in a different thread. But with all the different types of functions, I can't get the templates to work. #include `<functional`> int foo(void) {return 2;} class bar { public: int operator() (void) {return 4;}; int something(int a) {return a;}; }; template <class C> int func(C&& c) { //typedef typename std::result_of< C() >::type result_type; typedef typename std::conditional< std::is_pointer< C >::value, std::result_of< C() >::type, std::conditional< std::is_object< C >::value, std::result_of< typename C::operator() >::type, void> >::type result_type; result_type result = c(); return result; } int main(int argc, char* argv[]) { // call with a function pointer func(foo); // call with a member function bar b; func(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); // call with a lambda expression func( [](void)->int {return 12;} ); return 0; } The result_of template alone doesn't seem to be able to find the operator() in class bar and the clunky conditional I created doesn't compile. Any ideas? Will I have additional problems with const functions?

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• How is the C++ synthesized move constructor affected by volatile and virtual members?

  - by user1827766

  Look at the following code: struct node { node(); //node(const node&); //#1 //node(node&&); //#2 virtual //#3 ~node (); node* volatile //#4 next; }; main() { node m(node()); //#5 node n=node(); //#6 } When compiled with gcc-4.6.1 it produces the following error: g++ -g --std=c++0x -c -o node.o node.cc node.cc: In constructor node::node(node&&): node.cc:3:8: error: expression node::next has side-effects node.cc: In function int main(): node.cc:18:14: note: synthesized method node::node(node&&) first required here As I understand the compiler fails to create default move or copy constructor on line #6, if I uncomment either line #1 or #2 it compiles fine, that is clear. The code compiles fine without c++0x option, so the error is related to default move constructor. However, what in the node class prevents default move constructor to be created? If I comment any of the lines #3 or #4 (i.e. make the destructor non-virtual or make data member non-volatile) it compiles again, so is it the combination of these two makes it not to compile? Another puzzle, line #5 does not cause an compilation error, what is different from line #6? Is it all specific for gcc? or gcc-4.6.1?

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• C++ and Dependency Injection in unit testing

  - by lhumongous

  Suppose I have a C++ class like so: class A { public: A() { } void SetNewB( const B& _b ) { m_B = _b; } private: B m_B; } In order to unit test something like this, I would have to break A's dependency on B. Since class A holds onto an actual object and not a pointer, I would have to refactor this code to take a pointer. Additionally, I would need to create a parent interface class for B so I can pass in my own fake of B when I test SetNewB. In this case, doesn't unit testing with dependency injection further complicate the existing code? If I make B a pointer, I'm now introducing heap allocation, and some piece of code is now responsible for cleaning it up (unless I use ref counted pointers). Additionally, if B is a rather trivial class with only a couple of member variables and functions, why introduce a whole new interface for it instead of just testing with an instance of B? I suppose you could make the argument that it would be easier to refactor A by using an interface. But are there some cases where two classes might need to be tightly coupled?

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• C++ Declaring an enum within a class

  - by bporter

  In the following code snippet, the Color enum is declared within the Car class in order to limit the scope of the enum and to try not to "pollute" the global namespace. class Car { public: enum Color { RED, BLUE, WHITE }; void SetColor( Car::Color color ) { _color = color; } Car::Color GetColor() const { return _color; } private: Car::Color _color; }; (1) Is this a good way to limit the scope of the Color enum? Or, should I declare it outside of the Car class, but possibly within its own namespace or struct? I just came across this article today, which advocates the latter and discusses some nice points about enums: http://gamesfromwithin.com/stupid-c-tricks-2-better-enums. (2) In this example, when working within the class, is it best to code the enum as Car::Color, or would just Color suffice? (I assume the former is better, just in case there is another Color enum declared in the global namespace. That way, at least, we are explicit about the enum to we are referring.) Thanks in advance for any input on this.

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• C++ STL question related to insert iterators and overloaded operators

  - by rshepherd

  #include <list> #include <set> #include <iterator> #include <algorithm> using namespace std; class MyContainer { public: string value; MyContainer& operator=(const string& s) { this->value = s; return *this; } }; int main() { list<string> strings; strings.push_back("0"); strings.push_back("1"); strings.push_back("2"); set<MyContainer> containers; copy(strings.begin(), strings.end(), inserter(containers, containers.end())); } The preceeding code does not compile. In standard C++ fashion the error output is verbose and difficult to understand. The key part seems to be this... /usr/include/c++/4.4/bits/stl_algobase.h:313: error: no match for ‘operator=’ in ‘__result.std::insert_iterator::operator* [with _Container = std::set, std::allocator ]() = __first.std::_List_iterator::operator* [with _Tp = std::basic_string, std::allocator ]()’ ...which I interpet to mean that the assignment operator needed is not defined. I took a look at the source code for insert_iterator and noted that it has overloaded the assignment operator. The copy algorithm must uses the insert iterators overloaded assignment operator to do its work(?). I guess that because my input iterator is on a container of strings and my output iterator is on a container of MyContainers that the overloaded insert_iterator assignment operator can no longer work. This is my best guess, but I am probably wrong. So, why exactly does this not work and how can I accomplish what I am trying to do?

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• Why is T() = T() allowed?

  - by Rimo

  I believe the expression T() creates an rvalue (by the Standard). However, the following code compiles (at least on gcc4.0): class T {}; int main() { T() = T(); } I know technically this is possible because member functions can be invoked on temporaries and the above is just invoking the operator= on the rvalue temporary created from the first T(). But conceptually this is like assigning a new value to an rvalue. Is there a good reason why this is allowed? Edit: The reason I find this odd is it's strictly forbidden on built-in types yet allowed on user-defined types. For example, int(2) = int(3) won't compile because that is an "invalid lvalue in assignment". So I guess the real question is, was this somewhat inconsistent behavior built into the language for a reason? Or is it there for some historical reason? (E.g it would be conceptually more sound to allow only const member functions to be invoked on rvalue expressions, but that cannot be done because that might break some existing code.)

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• Filling a region draws it off canvas

  - by Xanyx

  Hi Using the following code in Delphi 2007: procedure TfrmTest.PaintBox1Paint(Sender: TObject); const Rect_Size = 10; begin PaintBox1.Canvas.Brush.Color := clYellow; PaintBox1.Canvas.FillRect(Rect(0, 0, PaintBox1.width, PaintBox1.height)); PaintBox1.Canvas.Brush.Color := clRed; DrawARect(PaintBox1.Canvas, 0, 0, Rect_Size, Rect_Size); end; procedure TfrmTest.DrawARect(ACanvas: TCanvas; iLeft, iTop, iWidth, iHeight: Integer); var rgnMain: HRGN; begin rgnMain := CreateRectRgn(iLeft, iTop, iLeft + iWidth, iTop + iHeight); try SelectClipRgn(ACanvas.handle, rgnMain); ACanvas.FillRect(ACanvas.ClipRect); SelectClipRgn(ACanvas.handle, 0); finally DeleteObject(rgnMain); end; end; I get this: (Yellow area shows boundaries of PaintBox1). HMMM, NOT ALLOWED TO POST IMAGE Please go to: http://www.freeimagehosting.net/uploads/62cf687d29.jpg (Linked image shows a form with a yellow box [PaintBox1] in the center. However my red rectange [rgnMain] has been drawn at pos 0,0 on the form) My expectation was that the red rectangle would be at the top left of the PaintBox1 canvas, not the form's canvas. Why is it not? Can regions only be used with controls that have a Windows handle? Thanks

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• Measuring the CPU frequency scaling effect

  - by Bryan Fok

  Recently I am trying to measure the effect of the cpu scaling. Is it accurate if I use this clock to measure it? template<std::intmax_t clock_freq> struct rdtsc_clock { typedef unsigned long long rep; typedef std::ratio<1, clock_freq> period; typedef std::chrono::duration<rep, period> duration; typedef std::chrono::time_point<rdtsc_clock> time_point; static const bool is_steady = true; static time_point now() noexcept { unsigned lo, hi; asm volatile("rdtsc" : "=a" (lo), "=d" (hi)); return time_point(duration(static_cast<rep>(hi) << 32 | lo)); } }; Update: According to the comment from my another post, I believe redtsc cannot use for measure the effect of cpu frequency scaling because the counter from the redtsc does not affected by the CPU frequency, am i right?

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• How to update a string property of an sqlite database item

  - by Thomas Joos

  hi all, I'm trying to write an application that checks if there is an active internet connection. If so it reads an xml and checks every 'lastupdated' item ( php generated string ). It compares it to the database items and if there is a new value, this particular item needs to be updated. My code seems to work ( compiles, no error messages, no failures, .. ) but I notice that the particular property does not change, it becomese (null). When I output the binded string value it returns the correct string value I want to update into the db.. Any idea what I'm doing wrong? const char *sql = "update myTable Set last_updated=? Where node_id =?"; sqlite3_stmt *statement; // Preparing a statement compiles the SQL query into a byte-code program in the SQLite library. // The third parameter is either the length of the SQL string or -1 to read up to the first null terminator. if (sqlite3_prepare_v2(database, sql, -1, &statement, NULL) == SQLITE_OK){ NSLog(@"last updated item: %@", [d lastupdated]); sqlite3_bind_text(statement, 1, [d lastupdated],-1,SQLITE_TRANSIENT); sqlite3_bind_int (statement, 2, [d node_id]); }else { NSLog(@"SQLite statement error!"); } if(SQLITE_DONE != sqlite3_step(statement)){ NSAssert1(0, @"Error while updating. '%s'", sqlite3_errmsg(database)); }else { NSLog(@"SQLite Update done!"); }

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• Which C++ Standard Library wrapper functions do you use?

  - by Neil Butterworth

  This question, asked this morning, made me wonder which features you think are missing from the C++ Standard Library, and how you have gone about filling the gaps with wrapper functions. For example, my own utility library has this function for vector append: template <class T> std::vector<T> & operator += ( std::vector<T> & v1, const std::vector <T> & v2 ) { v1.insert( v1.end(), v2.begin(), v2.end() ); return v1; } and this one for clearing (more or less) any type - particularly useful for things like std::stack: template <class C> void Clear( C & c ) { c = C(); } I have a few more, but I'm interested in which ones you use? Please limit answers to wrapper functions - i.e. no more than a couple of lines of code.

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• OpenSceneGraph C++ Access Violation reading location 0x00421000

  - by Kobojunkie

  Working with OpenSceneGraph, and I keep running into this violation issue that I would appreciate some help with. The problem is with the particular line below which happens to be the first in my main function. osg::ref_ptr<osg::Node> bench = osgDB::readNodeFile("Models/test.IVE"); I have my models folder right in my directory. The error is as below. Unhandled exception at 0x68630A6C (msvcr100.dll) in OSG3D.exe: 0xC0000005: Access violation reading location 0x00421000. And this is where the problem seems to be coming up. /** Read an osg::Node from file. * Return valid osg::Node on success, * return NULL on failure. * The osgDB::Registry is used to load the appropriate ReaderWriter plugin * for the filename extension, and this plugin then handles the request * to read the specified file.*/ inline osg::Node* readNodeFile(const std::string& filename) { return readNodeFile(filename,Registry::instance()->getOptions()); } I would appreciate details on how best to tackle this kind of exception message in the future. Are there tools that make this easy to debug or are there ways to capture the exact issues and fix them? I would appreciate any help with this. My ultimate goal is to learn how to better debug C++ related issues please. With this, it means reading through the compiler error list http://msdn.microsoft.com/en-us/library/850cstw1(v=vs.71).aspx is not enough

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• uninitialized local variable

  - by blitzeus

  This code compiles and runs though gives a Microsoft compiler error that I cant fix warning C4700: uninitialized local variable 'ptr4D' used. This is in the last line of the code, I think #include <iostream> using namespace std; const int DIM0 = 2, DIM1 = 3, DIM2 = 4, DIM3 = 5; void TestDeclar(); int main(){ TestDeclar(); cout << "Done!\n"; return 0; } void TestDeclar(){ //24 - array of 5 floats float xa[DIM3], xb[DIM3], xc[DIM3], xd[DIM3], xe[DIM3], xf[DIM3]; float xg[DIM3], xh[DIM3], xi[DIM3], xj[DIM3], xk[DIM3], xl[DIM3]; float xm[DIM3], xn[DIM3], xo[DIM3], xp[DIM3], xq[DIM3], xr[DIM3]; float xs[DIM3], xt[DIM3], xu[DIM3], xv[DIM3], xw[DIM3], xx[DIM3]; //6 - array of 4 pointers to floats float *ya[DIM2] = {xa, xb, xc, xd}, *yb[DIM2] = {xe, xf, xg, xh}; float *yc[DIM2] = {xi, xj, xk, xl}, *yd[DIM2] = {xm, xn, xo, xp}; float *ye[DIM2] = {xq, xr, xs, xt}, *yf[DIM2] = {xu, xv, xw, xx}; //2 - array of 3 pointers to pointers of floats float **za[DIM1] = {ya, yb, yc}; float **zb[DIM1] = {yd, ye, yf}; //array of 2 pointers to pointers to pointers of floats float ***ptr4D[DIM0] = {za, zb}; cout << &***ptr4D[DIM0] << '\n'; }

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• Optimization of a c++ matrix/bitmap class

  - by Andrew

  I am searching a 2D matrix (or bitmap) class which is flexible but also fast element access. The contents A flexible class should allow you to choose dimensions during runtime, and would look something like this (simplified): class Matrix { public: Matrix(int w, int h) : data(new int[x*y]), width(w) {} void SetElement(int x, int y, int val) { data[x+y*width] = val; } // ... private: // symbols int width; int* data; }; A faster often proposed solution using templates is (simplified): template <int W, int H> class TMatrix { TMatrix() data(new int[W*H]) {} void SetElement(int x, int y, int val) { data[x+y*W] = val; } private: int* data; }; This is faster as the width can be "inlined" in the code. The first solution does not do this. However this is not very flexible anymore, as you can't change the size anymore at runtime. So my question is: Is there a possibility to tell the compiler to generate faster code (like when using the template solution), when the size in the code is fixed and generate flexible code when its runtime dependend? I tried to achieve this by writing "const" where ever possible. I tried it with gcc and VS2005, but no success. This kind of optimization would be useful for many other similar cases.

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