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• C programming: Dereferencing pointer to incomplete type error

  - by confusedKid

  Hi, I am pretty rusty at C, and I'm getting a dereferencing error. Hopefully someone can help me with this? ^_^ I have a struct defined as: struct { char name[32]; int size; int start; int popularity; } stasher_file; and an array of pointers to those structs: struct stasher_file *files[TOTAL_STORAGE_SIZE]; In my code, I'm making a pointer to the struct and setting its members, and adding it to the array: ... struct stasher_file *newFile; strncpy(newFile-name, name, 32); newFile-size = size; newFile-start = first_free; newFile-popularity = 0; files[num_files] = newFile; ... I'm getting a "error: dereferencing pointer to incomplete type" whenever I try to access the members inside newFile. What am I doing wrong? Thanks very much for any help :)

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• Using GCC (MinGW) to compile OpenGL on Windows

  - by Casey

  I've searched on google and haven't been able to come up with a solution. I would like to compile some OpenGL programming using GCC. In the GL folder in GCC I have the following headers: gl.h glext.h glu.h Then in my system32 file I have the following .dll opengl32.dll glu32.dll glut32.dll If I wanted to write a simple OpenGL "Hello World" and link and compile with GCC, what is the correct process? I'm attempting to use this code: #include <GL/gl.h> #include <GL/glut.h> void display() { glClear(GL_COLOR_BUFFER_BIT); glFlush(); } int main(int argc, char **argv) { glutInit(&argc, argv); glutInitWindowSize(512,512); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutCreateWindow("The glut hello world program"); glutDisplayFunc(display); glClearColor(0.0, 0.0, 0.0, 1.0); glutMainLoop(); // Infinite event loop return 0; } Thank you in advance for the help.

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• How to produce output using show function.

  - by wilson88

  I am trying to use sho to show the output of another function.The first function was used to do sorting, and returned a List. now I want to make a function that uses show() to display the output.This is how I had tried it only to get an error. Its to diplay the results of two the two sorted lists which used this function. map Auctioneer::compareBidList(map& one, map& two) and //**return Sorted.** void show(const char *msg, map<int, Bid*>& Sorted) { cout << msg << endl; show(Sorted); } void compare(map<int, Bid*>& sellers, map<int, Bid*>& buyers) { compare(sellers.begin(), sellers.end(), buyers.begin(),buyers.end(),compareBidList); } //my call in the main after declaration was as follows map<int, Bid*> buyers, sellers; Auctioneer auctioneer; auctioneer.compare(sellers,buyers); show(("Bids after sorting:", sellers,buyers);)

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• Help regarding Android NDK

  - by Siva Kumar

  I am a beginner in using Android NDK. I am using Eclipse and I installed cygwin to build the c file to generate the .so file But while building the c file in cygwin I am always getting the error make: ***No rule to make target 'file.c' ... .Stop I tried building different C codes but for every file it says the same error .. Here is the source code: public class ndktest extends Activity { static { System.loadLibrary("ndkt"); } private native void helloLog(String logThis); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); helloLog("this is to test log file"); } } file.c void Java_com_ndktest_helloLog(JNIEnv * env, jobject this, jstring logThis) { jboolean isCopy; const char * szLogThis = (*env)->GetStringUTFChars(env, logThis, &isCopy); (*env)->ReleaseStringUTFChars(env, logThis, szLogThis); } And here is my Android.mk LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_LDLIBS := -llog LOCAL_MODULE := ndkt LOCAL_SRC_FILES := file.c include $(BUILD_SHARED_LIBRARY) I searched for the solution for the cause of error ... but nothing works for me. Can anyone tell me where I am making the mistake ? Thanks, Siva Kumar

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• How to make gcc on SUN calculate floating points the same way as in Linux

  - by Marina

  I have a project where I have to perform some mathematics calculations with double variables. The problem is that I get different results on SUN Solaris 9 and Linux. There are a lot of ways (explained here and other forums) how to make Linux work as Sun, but not the other way around. I cannot touch the Linux code, so it is only SUN I can change. Is there any way to make SUN to behave as Linux? The code I run(compile with gcc on both systems): int hash_func(char *long_id) { double product, lnum, gold; while (*long_id) lnum = lnum * 10.0 + (*long_id++ - '0'); printf("lnum => %20.20f\n", lnum); lnum = lnum * 10.0E-8; printf("lnum => %20.20f\n", lnum); gold = 0.6125423371582974; product = lnum * gold; printf("product => %20.20f\n", product); ... } if the input is 339886769243483 the output in Linux: lnum => 339886769243**483**.00000000000000000000 lnum => 33988676.9243**4829473495483398** product => 20819503.600158**59827399253845** When on SUN: lnum => 339886769243483.00000000000000000000 lnum => 33988676.92434830218553543091 product = 20819503.600158**60199928283691** Note: The result is not always different, moreover most of the times it is the same. Just 10 15-digit numbers out of 60000 have this problem. Please help!!!

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• How to reuse results with a schema for end of day stock-data

  - by Vishalrix

  I am creating a database schema to be used for technical analysis like top-volume gainers, top-price gainers etc.I have checked answers to questions here, like the design question. Having taken the hint from boe100 's answer there I have a schema modeled pretty much on it, thusly: Symbol - char 6 //primary Date - date //primary Open - decimal 18, 4 High - decimal 18, 4 Low - decimal 18, 4 Close - decimal 18, 4 Volume - int Right now this table containing End Of Day( EOD) data will be about 3 million rows for 3 years. Later when I get/need more data it could be 20 million rows. The front end will be asking requests like "give me the top price gainers on date X over Y days". That request is one of the simpler ones, and as such is not too costly, time wise, I assume. But a request like " give me top volume gainers for the last 10 days, with the previous 100 days acting as baseline", could prove 10-100 times costlier. The result of such a request would be a float which signifies how many times the volume as grown etc. One option I have is adding a column for each such result. And if the user asks for volume gain in 10 days over 20 days, that would require another table. The total such tables could easily cross 100, specially if I start using other results as tables, like MACD-10, MACD-100. each of which will require its own column. Is this a feasible solution? Another option being that I keep the result in cached html files and present them to the user. I dont have much experience in web-development, so to me it looks messy; but I could be wrong ( ofc!) . Is that a option too? Let me add that I am/will be using mod_perl to present the response to the user. With much of the work on mysql database being done using perl. I would like to have a response time of 1-2 seconds.

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• [MFC] Creating multiple dialogs in an MFC app with no main Window, they become children of each othe

  - by John

  (title updated) Following on from this question, now I have a clearer picture what's going on... I have a MFC application with no main window, which exposes an API to create dialogs. When I call some of these methods repeatedly, the dialogs created are parented to each other instead of all being parented to the desktop... I have no idea why. But anyway even after creation, I am unable to change the parent back to NULL or CWnd::GetDesktopWindow()... if I call SetParent followed by GetParent, nothing has changed. So apart from the really weird question of why Windows is magically parenting each dialog to the last one created, is there anything I'm missing to be able to set these windows as children of the desktop? UPDATED: I have found the reason for all this, but not the solution. From my dialog constructor, we end up in: BOOL CDialog::CreateIndirect(LPCDLGTEMPLATE lpDialogTemplate, CWnd* pParentWnd, void* lpDialogInit, HINSTANCE hInst) { ASSERT(lpDialogTemplate != NULL); if (pParentWnd == NULL) pParentWnd = AfxGetMainWnd(); m_lpDialogInit = lpDialogInit; return CreateDlgIndirect(lpDialogTemplate, pParentWnd, hInst); } Note: if (pParentWnd == NULL)pParentWnd = AfxGetMainWnd(); The call-stack from my dialog constructor looks like this: mfc80d.dll!CDialog::CreateIndirect(const DLGTEMPLATE * lpDialogTemplate=0x005931a8, CWnd * pParentWnd=0x00000000, void * lpDialogInit=0x00000000, HINSTANCE__ * hInst=0x00400000) mfc80d.dll!CDialog::CreateIndirect(void * hDialogTemplate=0x005931a8, CWnd * pParentWnd=0x00000000, HINSTANCE__ * hInst=0x00400000) mfc80d.dll!CDialog::Create(const char * lpszTemplateName=0x0000009d, CWnd * pParentWnd=0x00000000) mfc80d.dll!CDialog::Create(unsigned int nIDTemplate=157, CWnd * pParentWnd=0x00000000) MyApp.exe!CMyDlg::CMyDlg(CWnd * pParent=0x00000000) Running in the debugger, if I manually change pParentWnd back to 0 in CDialog::CreateIndirect, everything works fine... but how do I stop it happening in the first place?

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• C: 8x8 -> 16 bit multiply precision guaranteed by integer promotions?

  - by craig-blome

  I'm trying to figure out if the C Standard (C90, though I'm working off Derek Jones' annotated C99 book) guarantees that I will not lose precision multiplying two unsigned 8-bit values and storing to a 16-bit result. An example statement is as follows: unsigned char foo; unsigned int foo_u16 = foo * 10; Our Keil 8051 compiler (v7.50 at present) will generate a MUL AB instruction which stores the MSB in the B register and the LSB in the accumulator. If I cast foo to a unsigned int first: unsigned int foo_u16 = (unsigned int)foo * 10; then the compiler correctly decides I want a unsigned int there and generates an expensive call to a 16x16 bit integer multiply routine. I would like to argue beyond reasonable doubt that this defensive measure is not necessary. As I read the integer promotions described in 6.3.1.1, the effect of the first line shall be as if foo and 10 were promoted to unsigned int, the multiplication performed, and the result stored as unsigned int in foo_u16. If the compiler knows an instruction that does 8x8-16 bit multiplications without loss of precision, so much the better; but the precision is guaranteed. Am I reading this correctly? Best regards, Craig Blome

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• jscript1.js error in webforms when applying routing

  - by Sean N

  Hello I have a project using webforms. I applied routing on one of the page. My route is structure like this : http://localhost:3576/Request/Admin/Rejected/ = http://localhost:3576/Request/{role}/{action}/{id} Everything works great but i have a javascript error: Webpage error details User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; InfoPath.2; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729) Timestamp: Fri, 7 May 2010 13:35:54 UTC Message: Syntax error Line: 3 Char: 1 Code: 0 URI: http://localhost:3576/Request/Admin/Rejected/JScript1.js I think it's trying to route to the file where i stored my javascript functions. Any suggestion?

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• SDL with OpenGL (freeglut) crashes on call to glutBitmapCharacter

  - by stett

  I have a program using OpenGL through freeglut under SDL. The SDL/OpenGL initialization is as follows: // Initialize SDL SDL_Init(SDL_INIT_VIDEO); // Create the SDL window SDL_SetVideoMode(SCREEN_W, SCREEN_H, SCREEN_DEPTH, SDL_OPENGL); // Initialize OpenGL glClearColor(BG_COLOR_R, BG_COLOR_G, BG_COLOR_B, 1.f); glViewport(0, 0, SCREEN_W, SCREEN_H); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(0.0f, SCREEN_W, SCREEN_H, 0.0f, -1.0f, 1.0f); glEnable(GL_TEXTURE_2D); glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); I've been using glBegin() ... glEnd() blocks without any trouble to draw primitives. However, in this program when I call any glutBitmapX function, the program simply exits without an error status. The code I'm using to draw text is: glColor3f(1.f, 1.f, 1.f); glRasterPos2f(x, y); glutStrokeString(GLUT_BITMAP_8_BY_13, (const unsigned char*)"test string"); In previous similar programs I've used glutBitmapCharacter and glutStrokeString to draw text and it's seemed to work. The only difference being that I'm using freeglut with SDL now instead of just GLUT as I did in previous programs. Is there some fundamental problem with my setup that I'm not seeing, or is there a better way of drawing text?

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• Why do I get two clicked or released signals when using a custom slot for a QPushButton ?

  - by Chris

  here's the main code at first I thought is was the message box but setting a label instead has the same effect. #include <time.h> #include "ui_mainwindow.h" #include <QMessageBox> class MainWindow : public QWidget, private Ui::MainWindow { Q_OBJECT public: MainWindow(QWidget *parent = 0); void makeSum(void); private: int r1; int r2; private slots: void on_pushButton_released(void); }; MainWindow::MainWindow(QWidget *parent) : QWidget(parent) { setupUi(this); } void MainWindow::on_pushButton_released(void) { bool ok; int a = lineEdit->text().toInt(&ok, 10); if (ok) { if (r1+r2==a) { QMessageBox::information( this, "Sums","Correct!" ); } else { QMessageBox::information( this, "Sums","Wrong!" ); } } else { QMessageBox::information( this, "Sums","You need to enter a number" ); } makeSum(); } void MainWindow::makeSum(void) { r1 = rand() % 10 + 1; r2 = rand() % 10 + 1; label->setText(QString::number(r1)); label_3->setText(QString::number(r2)); } int main(int argc, char *argv[]) { srand ( time(NULL) ); QApplication app(argc, argv); MainWindow mw; mw.makeSum(); mw.show(); return app.exec(); } #include "main.moc"

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• tail call generated by clang 1.1 and 1.0 (llvm 2.7 and 2.6)

  - by ony

  After compilation next snippet of code with clang -O2 (or with online demo): #include <stdio.h> #include <stdlib.h> int flop(int x); int flip(int x) { if (x == 0) return 1; return (x+1)*flop(x-1); } int flop(int x) { if (x == 0) return 1; return (x+0)*flip(x-1); } int main(int argc, char **argv) { printf("%d\n", flip(atoi(argv[1]))); } I'm getting next snippet of llvm assembly in flip: bb1.i: ; preds = %bb1 %4 = add nsw i32 %x, -2 ; <i32> [#uses=1] %5 = tail call i32 @flip(i32 %4) nounwind ; <i32> [#uses=1] %6 = mul nsw i32 %5, %2 ; <i32> [#uses=1] br label %flop.exit I thought that tail call means dropping current stack (i.e. return will be to the upper frame, so next instruction should be ret %5), but according to this code it will do mul for it. And in native assembly there is simple call without tail optimisation (even with appropriate flag for llc) Can sombody explain why clang generates such code? As well I can't understand why llvm have tail call if it can simply check that next ret will use result of prev call and later do appropriate optimisation or generate native equivalent of tail-call instruction?

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• PowerShell PSCX Read-Archive: Cannot bind parameter... problem

  - by Robert

  I'm running across a problem I can't seem to wrap my head around using the Read-Archive cmdlet available via PowerShell Community Extensions (v2.0.3782.38614). Here is a cut down sample used to exhibit the problem I'm running into: $mainPath = "p:\temp" $dest = Join-Path $mainPath "ps\CenCodes.zip" Read-Archive -Path $dest -Format zip Running the above produces the following error: Read-Archive : Cannot bind parameter 'Path'. Cannot convert the "p:\temp\ps\CenCodes.zip" value of type "System.String" to type "Pscx.IO.PscxPathInfo". At line:3 char:19 + Read-Archive -Path <<<< $dest -Format zip + CategoryInfo : InvalidArgument: (:) [Read-Archive], ParameterBindingException + FullyQualifiedErrorId : CannotConvertArgumentNoMessage,Pscx.Commands.IO.Compression.ReadArchiveCommand If I do not use Join-Path to build the path passed to Read-Archive it works, as in this example: $mainPath = "p:\temp" $path = $mainPath + "\ps\CenCodes.zip" Read-Archive -Path $path -Format zip Output from above: ZIP Folder: CenCodes.zip#\ Index LastWriteTime Size Ratio Name ----- ------------- ---- ----- ---- 0 6/17/2010 2:03 AM 3009106 24.53 % CenCodes.xls Even more confusing is if I compare the two variables passed as the Path argument in the two Read-Archive samples above, they seem identical: This... Write-Host "dest=$dest" Write-Host "path=$path" Write-Host ("path -eq dest is " + ($dest -eq $path).ToString()) Outputs... dest=p:\temp\ps\CenCodes.zip path=p:\temp\ps\CenCodes.zip path -eq dest is True Anyone have any ideas as to why the first sample gripes but the second one works fine?

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• recommended format to save time with MJD + BCD format in database

  - by pierr

  Hi, There is a time represented in MJD and BCD format with 5 bytes .I am wondering what is the recommended format to save this date-time in the sqlite database so that user can search against it ? My first attempt is to save it just as it is, that is a 5 bytes string. The user will use the same format to search and the result will be converted to unix time by the user with following code. However, later, I was suggested to save the time in the integer - the UTC time, for example. But I can not find a standard way to do the conversion. I feel this is a common issue and would like to hear your comments. time_t sidate_to_unixtime(unsigned char sidate[]) { int k = 0; struct tm tm; double mjd; /* check for the undefined value */ if ((sidate[0] == 0xff) && (sidate[1] == 0xff) && (sidate[2] == 0xff) && (sidate[3] == 0xff) && (sidate[4] == 0xff)) { return -1; } memset(&tm, 0, sizeof(tm)); mjd = (sidate[0] << 8) | sidate[1]; tm.tm_year = (int) ((mjd - 15078.2) / 365.25); tm.tm_mon = (int) (((mjd - 14956.1) - (int) (tm.tm_year * 365.25)) / 30.6001); tm.tm_mday = (int) mjd - 14956 - (int) (tm.tm_year * 365.25) - (int) (tm.tm_mon * 30.6001); if ((tm.tm_mon == 14) || (tm.tm_mon == 15)) k = 1; tm.tm_year += k; tm.tm_mon = tm.tm_mon - 2 - k * 12; tm.tm_sec = bcd_to_integer(sidate[4]); tm.tm_min = bcd_to_integer(sidate[3]); tm.tm_hour = bcd_to_integer(sidate[2]); return mktime(&tm); }

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• An Interactive Console I/O Wrapper/Interceptor in C# - What is the issue?

  - by amazedsaint

  I was trying to put together an interactive Console interceptor/wrapper in C# over the weekend, by re-mixing few code samples I've found in SO and other sites. With what I've as of now, I'm unable to read back from the console reliably. Any quick pointers? public class ConsoleInterceptor { Process _interProc; public event Action<string> OutputReceivedEvent; public ConsoleInterceptor() { _interProc = new Process(); _interProc.StartInfo = new ProcessStartInfo("cmd"); InitializeInterpreter(); } public ConsoleInterceptor(string command) { _interProc = new Process(); _interProc.StartInfo = new ProcessStartInfo(command); InitializeInterpreter(); } public Process InterProc { get { return _interProc; } } private void InitializeInterpreter() { InterProc.StartInfo.RedirectStandardInput = true; InterProc.StartInfo.RedirectStandardOutput = true; InterProc.StartInfo.RedirectStandardError = true; InterProc.StartInfo.CreateNoWindow = true; InterProc.StartInfo.UseShellExecute = false; InterProc.StartInfo.WindowStyle = ProcessWindowStyle.Hidden; bool started = InterProc.Start(); Redirect(InterProc.StandardOutput); Redirect(InterProc.StandardError); } private void Redirect(StreamReader input) { new Thread((a) => { var buffer = new char[1]; while (true) { if (input.Read(buffer, 0, 1) > 0) OutputReceived(new string(buffer)); }; }).Start(); } private void OutputReceived(string text) { if (OutputReceivedEvent != null) OutputReceivedEvent(text); } public void Input(string input) { InterProc.StandardInput.WriteLine(input); InterProc.StandardInput.Flush(); } }

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• What's wrong with my code? (pdcurses/getmaxyx)

  - by flarn2006

  It gives me an access violation on the getmaxyx line (second line in the main function) and also gives me these two warnings: LINK : warning LNK4049: locally defined symbol "_stdscr" imported LINK : warning LNK4049: locally defined symbol "_SP" imported Yes, it's the same code as in another question I asked, it's just that I'm making it more clear. And yes, I have written programs with pdcurses before with no problems. #include <time.h> #include <curses.h> #include "Ball.h" #include "Paddle.h" #include "config.h" int main(int argc, char *argv[]) { int maxY, maxX; getmaxyx(stdscr, maxY, maxX); Paddle *paddleLeft = new Paddle(0, KEY_L_UP, KEY_L_DOWN); Paddle *paddleRight = new Paddle(maxX, KEY_R_UP, KEY_R_DOWN); Ball *ball = new Ball(paddleLeft, paddleRight); int key = 0; initscr(); cbreak(); noecho(); curs_set(0); while (key != KEY_QUIT) { key = getch(); paddleLeft->OnKeyPress(key); paddleRight->OnKeyPress(key); } endwin(); return 0; }

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• Binary files printing and desired precision

  - by yCalleecharan

  Hi, I'm printing a variable say z1 which is a 1-D array containing floating point numbers to a text file so that I can import into Matlab or GNUPlot for plotting. I've heard that binary files (.dat) are smaller than .txt files. The definition that I currently use for printing to a .txt file is: void create_out_file(const char *file_name, const long double *z1, size_t z_size){ FILE *out; size_t i; if((out = _fsopen(file_name, "w+", _SH_DENYWR)) == NULL){ fprintf(stderr, "***> Open error on output file %s", file_name); exit(-1); } for(i = 0; i < z_size; i++) fprintf(out, "%.16Le\n", z1[i]); fclose(out); } I have three questions: Are binary files really more compact than text files?; If yes, I would like to know how to modify the above code so that I can print the values of the array z1 to a binary file. I've read that fprintf has to be replaced with fwrite. My output file say dodo.dat should contain the values of array z1 with one floating number per line. I have %.16Le up in my code but I think that %.15Le is right as I have 15 precision digits with long double. I have put a dot (.) in the width position as I believe that this allows expansion to an arbitrary field to hold the desired number. Am I right? As an example with %.16Le, I can have an output like 1.0047914240730432e-002 which gives me 16 precision digits and the width of the field has the right width to display the number correctly. Is placing a dot (.) in the width position instead of a width value a good practice? Thanks a lot...

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• Is extending a base class with non-virtual destructor dangerous in C++

  - by Akusete

  Take the following code class A { }; class B : public A { }; class C : public A { int x; }; int main (int argc, char** argv) { A* b = new B(); A* c = new C(); //in both cases, only ~A() is called, not ~B() or ~C() delete b; //is this ok? delete c; //does this line leak memory? return 0; } when calling delete on a class with a non-virtual destructor with member functions (like class C), can the memory allocator tell what the proper size of the object is? If not, is memory leaked? Secondly, if the class has no member functions, and no explicit destructor behaviour (like class B), is everything ok? I ask this because I wanted to create a class to extend std::string, (which I know is not recommended, but for the sake of the discussion just bear with it), and overload the +=,+ operator. -Weffc++ gives me a warning because std::string has a non virtual destructor, but does it matter if the sub-class has no members and does not need to do anything in its destructor? -- FYI the += overload was to do proper file path formatting, so the path class could be used like class path : public std::string { //... overload, +=, + //... add last_path_component, remove_path_component, ext, etc... }; path foo = "/some/file/path"; foo = foo + "filename.txt"; //and so on... I just wanted to make sure someone doing this path* foo = new path(); std::string* bar = foo; delete bar; would not cause any problems with memory allocation

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• PDCurses TUI with C++ Win32 console application

  - by Bach

  I have downloaded pdcurses source and was able to successfully include curses.h in my project, linked the pre-compiled library and all good. After few hours of trying out the library, I saw the tuidemo.c in the demos folder, compiled it into an executable and brilliant! exactly what I needed for my project. Now the problem is that it's a C code, and I am working on a C++ project in VS c++ 2008. The files I need are tui.c and tui.h How can I include that C file in my C++ code? I saw few suggestions here but the compiler was not too happy with 100's of warnings and errors. How can I go on including/using that TUI pdcurses includes!? Thanks EDIT: I added extern "C" statement, so my test looks like this now, but I'm getting some other type of error #include <stdio.h> #include <stdlib.h> using namespace std; extern "C" { #include <tui.h> } void sub0(void) { //do nothing } void sub1(void) { //do nothing } int main (int argc, char * const argv[]) { menu MainMenu[] = { { "Asub", sub0, "Go inside first submenu" }, { "Bsub", sub1, "Go inside second submenu" }, { "", (FUNC)0, "" } /* always add this as the last item! */ }; startmenu(MainMenu, "TUI - 'textual user interface' demonstration program"); return 0; } Although it is compiling successfully, it is throwing an Error at runtime: 0xC0000005: Access violation reading location 0x021c52f9 at line startmenu(MainMenu, "TUI - 'textual user interface' demonstration program"); Not sure where to go from here. thanks again.

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• c++ Mixing printf with wprintf (or cout with wcout)

  - by Bo Jensen

  I know you should not mix printing with printf,cout and wprintf,wcout, but have a hard time finding a good answer why and if it is possible to get round it. The problem is I use a external library that prints with printf and my own uses wcout. If I do a simple example it works fine, but from my full application it simply does not print the printf statements. If this is really a limitation, then there would be many libraries out there which can not work together with wide printing applications. Any insight on this is more than welcome. Update : I boiled it down to : #include <stdio.h> #include <stdlib.h> #include <iostream> #include <readline/readline.h> #include <readline/history.h> int main() { char *buf; std::wcout << std::endl; /* ADDING THIS LINE MAKES PRINTF VANISH!!! */ rl_bind_key('\t',rl_abort);//disable auto-complete while((buf = readline("my-command : "))!=NULL) { if (strcmp(buf,"quit")==0) break; std::wcout<<buf<< std::endl; if (buf[0]!=0) add_history(buf); } free(buf); return 0; } So I guess it might be a flushing problem, but it still looks strange to me, I have to check up on it.

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• Volatile fields in C#

  - by Danny Chen

  From the specification 10.5.3 Volatile fields: The type of a volatile field must be one of the following: A reference-type. The type byte, sbyte, short, ushort, int, uint, char, float, bool, System.IntPtr, or System.UIntPtr. An enum-type having an enum base type of byte, sbyte, short, ushort, int, or uint. First I want to confirm my understanding is correct: I guess the above types can be volatile because they are stored as a 4-bytes unit in memory(for reference types because of its address), which guarantees the read/write operation is atomic. A double/long/etc type can't be volatile because they are not atomic reading/writing since they are more than 4 bytes in memory. Is my understanding correct? And the second, if the first guess is correct, why a user defined struct with only one int field in it(or something similar, 4 bytes is ok) can't be volatile? Theoretically it's atomic right? Or it's not allowed simply because that all user defined structs(which is possibly more than 4 bytes) are not allowed to volatile by design?

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• Is my method for avoiding dynamic_cast<> faster than dynamic_cast<> itself ?

  - by ereOn

  Hi, I was answering a question a few minutes ago and it raised to me another one: In one of my projects, I do some network message parsing. The messages are in the form of: [1 byte message type][2 bytes payload length][x bytes payload] The format and content of the payload are determined by the message type. I have a class hierarchy, based on a common class Message. To instanciate my messages, i have a static parsing method which gives back a Message* depending on the message type byte. Something like: Message* parse(const char* frame) { // This is sample code, in real life I obviously check that the buffer // is not NULL, and the size, and so on. switch(frame[0]) { case 0x01: return new FooMessage(); case 0x02: return new BarMessage(); } // Throw an exception here because the mesage type is unknown. } I sometimes need to access the methods of the subclasses. Since my network message handling must be fast, I decived to avoid dynamic_cast<> and I added a method to the base Message class that gives back the message type. Depending on this return value, I use a static_cast<> to the right child type instead. I did this mainly because I was told once that dynamic_cast<> was slow. However, I don't know exactly what it really does and how slow it is, thus, my method might be as just as slow (or slower) but far more complicated. What do you guys think of this design ? Is it common ? Is it really faster than using dynamic_cast<> ? Any detailed explanation of what happen under the hood when one use dynamic_cast<> is welcome !

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• How to asynchronously read to std::string using Boost::asio?

  - by SpyBot

  Hello. I'm learning Boost::asio and all that async stuff. How can I asynchronously read to variable user_ of type std::string? Boost::asio::buffer(user_) works only with async_write(), but not with async_read(). It works with vector, so what is the reason for it not to work with string? Is there another way to do that besides declaring char user_[max_len] and using Boost::asio::buffer(user_, max_len)? Also, what's the point of inheriting from boost::enable_shared_from_this<Connection> and using shared_from_this() instead of this in async_read() and async_write()? I've seen that a lot in the examples. Here is a part of my code: class Connection { public: Connection(tcp::acceptor &acceptor) : acceptor_(acceptor), socket_(acceptor.get_io_service(), tcp::v4()) { } void start() { acceptor_.get_io_service().post( boost::bind(&Connection::start_accept, this)); } private: void start_accept() { acceptor_.async_accept(socket_, boost::bind(&Connection::handle_accept, this, placeholders::error)); } void handle_accept(const boost::system::error_code& err) { if (err) { disconnect(); } else { async_read(socket_, boost::asio::buffer(user_), boost::bind(&Connection::handle_user_read, this, placeholders::error, placeholders::bytes_transferred)); } } void handle_user_read(const boost::system::error_code& err, std::size_t bytes_transferred) { if ( err or (bytes_transferred != sizeof(user_)) ) { disconnect(); } else { ... } } ... void disconnect() { socket_.shutdown(tcp::socket::shutdown_both); socket_.close(); socket_.open(tcp::v4()); start_accept(); } tcp::acceptor &acceptor_; tcp::socket socket_; std::string user_; std::string pass_; ... };

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• how to get jquery.couch.app.js to work with IE8

  - by fuzzy lollipop

  I have tested this on Windows XP SP3 and Windows 7 Ultimate in IE7 and IE8 (in all compatiblity modes) and it fails the same way on both. I am running the latest HEAD from the the couchapp repository. This works fine on my OSX 10.6.3 development machine. I have tested with Chrome 4.1.249.1064 (45376) and Firefox 3.6 and they both work fine. As do the Safari 4 and Firefox 3.6 on OSX 10.6.3 Here is the error message Webpage error details User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0) Timestamp: Wed, 28 Apr 2010 03:32:55 UTC Message: Object doesn't support this property or method Line: 159 Char: 7 Code: 0 URI: http://192.168.0.105:5984/test/_design/test/vendor/couchapp/jquery.couch.app.js and here is the "offending" bit of code, which works on Chrome, Firefox and Safari just fine. If says the failure is on the like that qs.forEach() from the file jquery.couch.app.js 157 var qs = document.location.search.replace(/^\?/,'').split('&'); 158 var q = {}; 159 qs.forEach(function(param) { 160 var ps = param.split('='); 161 var k = decodeURIComponent(ps[0]); 162 var v = decodeURIComponent(ps[1]); 163 if (["startkey", "endkey", "key"].indexOf(k) != -1) { 164 q[k] = JSON.parse(v); 165 } else { 166 q[k] = v; 167 } 168 });

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• MySQL DDL error creating tables

  - by Alexandstein

  I am attempting to create tables for a MySQL database, but I am having some syntactical issues. It would seem that syntax checking is behaving differently between tables for some reason. While I've gotten all the other tables to go through, the table, 'stock' doesn't seem to be working, despite seeming to use the same syntax patterns. CREATE TABLE users ( user_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, username VARCHAR(30) NOT NULL, password CHAR(41) NOT NULL, date_joined DATETIME NOT NULL, funds DOUBLE UNSIGNED NOT NULL, PRIMARY KEY(user_id), UNIQUE KEY(username) ); CREATE TABLE owned_stocks ( id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, user_id SMALLINT UNSIGNED NOT NULL, paid_price DOUBLE UNSIGNED NOT NULL, quantity MEDIUMINT UNSIGNED NOT NULL, purchase_date DATETIME NOT NULL, PRIMARY KEY(id) ); CREATE TABLE tracking_stocks ( ticker VARCHAR(5) NOT NULL, user_id SMALLINT UNSIGNED NOT NULL, PRIMARY KEY(ticker) ); CREATE TABLE stocks ( ticker VARCHAR(5) NOT NULL, last DOUBLE UNSIGNED NOT NULL, high DOUBLE UNSIGNED NOT NULL, low DOUBLE UNSIGNED NOT NULL, company_name VARCHAR(30) NOT NULL, last_updated INT UNSIGNED NOT NULL, change DOUBLE NOT NULL, percent_change DOUBLE NOT NULL, PRIMARY KEY(ticker) ); Am I just missing a really obvious syntactical issue? ERROR: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'change DOUBLE NOT NULL, percent_change DOUBLE NOT NULL, last DOUBLE' at line 4

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