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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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• Weird Qt SSL issue -- error "No Error" shows up, nothing else, and if I ignore it, everything works

  - by houbysoft

  The issue is as follows : in my Qt app, I have a QWebView, which I use to load a HTTPS page. Everything worked fine on my development machine, so I'm now trying to get it to run on a test machine. I ran the app, but the page didn't load (the QWebView was blank). After much debugging, I found the problem is that an SSL error shows up, and the sslErrors() signal is fired. Here is my sslErrors() handling code: void blah::sslErrors(QNetworkReply *reply, const QList<QSslError> &errors) { foreach(QSslError error, errors) { qDebug() << error.errorString() << endl; } reply->ignoreSslErrors(); } The only thing the above code prints is: "No error" So there's no error, but unless I call reply->ignoreSslErrors(), the page doesn't load (on the test machine, on my developer computer no error is reported). Huh? Is this a bug? Is it safe to ignore the error, if I make sure it's of the type "No error"?

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• How to iterate over modifed std::map values?

  - by Frank

  I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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• Communication between parent and child

  - by Pierre

  Hi every one ! I have a little problem. I have to code a simple C application that creat a process and his child (fork()) and I have to do an operation. Parent initialize the values and child calculate. I write this : #include #include #include #include #include typedef struct { int op1; char op; int op2; }Operation; Operation *varOP; void finalResult() { float result = 0; if(varOP-op == '+') result = (varOP-op1 + varOP-op2); if(varOP-op == '-') result = (varOP-op1 - varOP-op2); if(varOP-op == '*') result = (varOP-op1 * varOP-op2); if(varOP-op == '+') result = (varOP-op1 / varOP-op2); printf("%f",result); } int main () { int p; varOP = (Operation *)malloc(sizeof(Operation)); p = fork(); if(p == 0) // If child { signal(SIGUSR1, finalResult ); pause(); } if(p 0) // If parent { varOP-op = '+'; varOP-op1 = 2; varOP-op2 = 3; kill(p, SIGUSR1); wait(NULL); } return 0; } But my child is never called. Is there something wrong with my code? Thanks for your help !

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• Rhino Mocks Partial Mock

  - by dotnet crazy kid

  I am trying to test the logic from some existing classes. It is not possible to re-factor the classes at present as they are very complex and in production. What I want to do is create a mock object and test a method that internally calls another method that is very hard to mock. So I want to just set a behaviour for the secondary method call. But when I setup the behaviour for the method, the code of the method is invoked and fails. Am I missing something or is this just not possible to test without re-factoring the class? I have tried all the different mock types (Strick,Stub,Dynamic,Partial ect.) but they all end up calling the method when I try to set up the behaviour. using System; using MbUnit.Framework; using Rhino.Mocks; namespace MMBusinessObjects.Tests { [TestFixture] public class PartialMockExampleFixture { [Test] public void Simple_Partial_Mock_Test() { const string param = "anything"; //setup mocks MockRepository mocks = new MockRepository(); var mockTestClass = mocks.StrictMock<TestClass>(); //record beahviour *** actualy call into the real method stub *** Expect.Call(mockTestClass.MethodToMock(param)).Return(true); //never get to here mocks.ReplayAll(); //this is what i want to test Assert.IsTrue(mockTestClass.MethodIWantToTest(param)); } public class TestClass { public bool MethodToMock(string param) { //some logic that is very hard to mock throw new NotImplementedException(); } public bool MethodIWantToTest(string param) { //this method calls the if( MethodToMock(param) ) { //some logic i want to test } return true; } } } }

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• Reading text files line by line, with exact offset/position reporting

  - by Benjamin Podszun

  Hi. My simple requirement: Reading a huge ( a million) line test file (For this example assume it's a CSV of some sorts) and keeping a reference to the beginning of that line for faster lookup in the future (read a line, starting at X). I tried the naive and easy way first, using a StreamWriter and accessing the underlying BaseStream.Position. Unfortunately that doesn't work as I intended: Given a file containing the following Foo Bar Baz Bla Fasel and this very simple code using (var sr = new StreamReader(@"C:\Temp\LineTest.txt")) { string line; long pos = sr.BaseStream.Position; while ((line = sr.ReadLine()) != null) { Console.Write("{0:d3} ", pos); Console.WriteLine(line); pos = sr.BaseStream.Position; } } the output is: 000 Foo 025 Bar 025 Baz 025 Bla 025 Fasel I can imagine that the stream is trying to be helpful/efficient and probably reads in (big) chunks whenever new data is necessary. For me this is bad.. The question, finally: Any way to get the (byte, char) offset while reading a file line by line without using a basic Stream and messing with \r \n \r\n and string encoding etc. manually? Not a big deal, really, I just don't like to build things that might exist already..

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• Using unset member variables within a class or struct

  - by Doug Kavendek

  It's pretty nice to catch some really obvious errors when using unset local variables or when accessing a class or struct's members directly prior to initializing them. In visual studio 2008 you get an "uninitialized local variable used" warning at compile-time and get a run-time check failure at the point of access when debugging. However, if you access an uninitialized struct's member variable through one of its functions, you don't get any warnings or assertions. Obviously the easiest solution is don't do that, but nobody's perfect. For example: struct Test { float GetMember() const { return member; } float member; }; Test test; float f1 = test.member; // Raises warning, asserts in VS debugger at runtime float f2 = test.GetMember(); // No problem, just keeps on going This surprised me, but it makes some sense -- the compiler can't assume calling a function on an unused struct is an error, or how else would you initialize or construct it? And anything fancier just quickly brings up so many other complications that it makes sense that it wouldn't bother classifying which functions are ok to call and when, especially just as a debugging help. I know I can set up my own assertions or error checking within the class itself, but that can complicate some simpler structs. Still, it would seem like within the context of the function call, wouldn't it know insides GetMember() that member wasn't initialized yet? I'm assuming it's not only relying on static compile-time deduction, given the Run-Time Check Failure #3 it raises during execution, so based on my current understanding of it it would seem reasonable for the same checks to apply. Is this just a limitation of this specific compiler/debugger (Visual Studio 2008), or more tied to how C++ works?

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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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• 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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• 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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• 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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• Weird problem with string function

  - by wrongusername

  I'm having a weird problem with the following function, which returns a string with all the characters in it after a certain point: string after(int after, string word) { char temp[word.size() - after]; cout << word.size() - after << endl; //output here is as expected for(int a = 0; a < (word.size() - after); a++) { cout << word[a + after]; //and so is this temp[a] = word[a + after]; cout << temp[a]; //and this } cout << endl << temp << endl; //but output here does not always match what I want string returnString = temp; return returnString; } The thing is, when the returned string is 7 chars or less, it works just as expected. When the returned string is 8 chars or more, then it starts spewing nonsense at the end of the expected output. For example, the lines cout << after(1, "12345678") << endl; cout << after(1, "123456789") << endl; gives an output of: 7 22334455667788 2345678 2345678 8 2233445566778899 23456789?,?D~ 23456789?,?D~ What can I do to fix this error, and are there any default C++ functions that can do this for me?

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• How to test for existence of a script-scoped variable in PowerShell?

  - by Damian Powell

  Is it possible to test for the existence of a script-scoped variable in PowerShell? I've been using the PowerShell Community Extensions (PSCX) but I've noticed that if you import the module while Set-PSDebug -Strict is set, an error is produced: The variable '$SCRIPT:helpCache' cannot be retrieved because it has not been set. At C:\Users\...\Modules\Pscx\Modules\GetHelp\Pscx.GetHelp.psm1:5 char:24 While investigating how I might fix this, I found this piece of code in Pscx.GetHelp.psm1: #requires -version 2.0 param([string[]]$PreCacheList) if ((!$SCRIPT:helpCache) -or $RefreshCache) { $SCRIPT:helpCache = @{} } This is pretty straight forward code; if the cache doesn't exist or needs to be refreshed, create a new, empty cache. The problem is that calling $SCRIPT:helpCache while Set-PSDebug -Strict is in force casues the error because the variable hasn't been defined yet. Ideally, we could use a Test-Variable cmdlet but such a thing doesn't exist! I thought about looking in the variable: provider but I don't know how to determine the scope of a variable. So my question is: how can I test for the existence of a variable while Set-PSDebug -Strict is in force, without causing an error?

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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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• 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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• KERN-EXEC 3 when navigating within a text box (Symbian OS Browser Control)

  - by Andrew Flanagan

  I've had nothing but grief using Symbian's browser control on S60 3rd edition FP1. We currently display pages and many things are working smoothly. However, when inputting text into an HTML text field, the user will get a KERN-EXEC 3 if they move left at the beginning of the text input area (which should "wrap" it to the end) or if they move right at the end of the text input area (which should "wrap" it to the beginning). I can't seem to trap the input in OfferKeyEventL. I get the key event, I return EKeyWasConsumed and the cursor still moves. TKeyResponse CMyAppContainer::OfferKeyEventL(const TKeyEvent& aKeyEvent, TEventCode aType) { if (iBrCtlInterface) // My browser control { TBrCtlDefs::TBrCtlElementType type = iBrCtlInterface->FocusedElementType(); if (type == TBrCtlDefs::EElementActivatedInputBox || type == TBrCtlDefs::EElementInputBox) { if (aKeyEvent.iScanCode == EStdKeyLeftArrow || aKeyEvent.iScanCode == EStdKeyRightArrow) { return EKeyWasConsumed; } } } } I would be okay with completely disabling arrow key navigation but can't seem to do this. Any ideas? Am I going about this the wrong way? Has anyone here even worked with the Browser Control library (browserengine.lib) on S60 3.1?

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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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• 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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• 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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• 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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• Using the Proxy pattern with C++ iterators

  - by Billy ONeal

  Hello everyone :) I've got a moderately complex iterator written which wraps the FindXFile apis on Win32. (See previous question) In order to avoid the overhead of constructing an object that essentially duplicates the work of the WIN32_FIND_DATAW structure, I have a proxy object which simply acts as a sort of const reference to the single WIN32_FIND_DATAW which is declared inside the noncopyable innards of the iterator. This is great because Clients do not pay for construction of irrelevant information they will probably not use (most of the time people are only interested in file names), and Clients can get at all the information provided by the FindXFile APIs if they need or want this information. This becomes an issue though because there is only ever a single copy of the object's actual data. Therefore, when the iterator is incrememnted, all of the proxies are invalidated (set to whatever the next file pointed to by the iterator is). I'm concerned if this is a major problem, because I can think of a case where the proxy object would not behave as somebody would expect: std::vector<MyIterator::value_type> files; std::copy(MyIterator("Hello"), MyIterator(), std::back_inserter(files)); because the vector contains nothing but a bunch of invalid proxies at that point. Instead, clients need to do something like: std::vector<std::wstring> filesToSearch; std::transform( DirectoryIterator<FilesOnly>(L"C:\\Windows\\*"), DirectoryIterator<FilesOnly>(), std::back_inserter(filesToSearch), std::mem_fun_ref(&DirectoryIterator<FilesOnly>::value_type::GetFullFileName) ); Seeing this, I can see why somebody might dislike what the standard library designers did with std::vector<bool>. I'm still wondering though: is this a reasonable trade off in order to achieve (1) and (2) above? If not, is there any way to still achieve (1) and (2) without the proxy?

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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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• I am trying to have a wall follow robot but there are errors on the names not being declared in my s

  - by Sam

  #include <iostream> #include <libplayerc++/playerc++.h> using namespace std; int main(int argc, char *argv[]) { using namespace PlayerCc; PlayerClient robot("localhost"); BumperProxy bp(&robot,0); Position2dProxy pp(&robot,0); pp.SetMotorEnable(true); for(;;) double turnrate, speed; double error; bool wall; motor_a_speed(0); motor_c_speed(0); while(1) { front_bumper = SENSOR_2; left_bumper = SENSOR_3; if (front_bumper > 2) { if (left_bumper < 3) { motor_a_speed(5); motor_c_speed(drive_speed); motor_a_dir(fwd); motor_c_dir(fwd); } else { motor_a_speed(drive_speed); motor_c_speed(5); motor_a_dir(rev); motor_c_dir(rev); } } else { motor_a_speed(drive_speed); motor_c_speed(drive_speed); motor_a_dir(brake); motor_c_dir(brake); mrest(100); cputs("bump"); motor_a_dir(fwd); motor_c_dir(rev); msleep(450); cputs("right"); motor_a_speed(10); motor_a_dir(fwd); motor_c_dir(fwd); mrest(1300); } pp.SetSpeed(speed, turnrate); } }

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• Function parameters evaluation order: is undefined behaviour if we pass reference?

  - by bolov

  This is undefined behaviour: void feedMeValue(int x, int a) { cout << x << " " << a << endl; } int main() { int a = 2; int &ra = a; feedMeValue(ra = 3, a); return 0; } because depending on what parameter gets evaluated first we could call (3, 2) or (3, 3). However this: void feedMeReference(int x, int const &ref) { cout << x << " " << ref << endl; } int main() { int a = 2; int &ra = a; feedMeReference(ra = 3, a); return 0; } will always output 3 3 since the second parameter is a reference and all parameters have been evaluated before the function call, so even if the second parameter is evaluated before of after ra = 3, the function received a reference to a wich will have a value of 2 or 3 at the time of the evaluation, but will always have the value 3 at the time of the function call. Is the second example UB? It is important to know because the compiler is free to do anything if he detects undefined behaviour, even if I know it would always yield the same results. *Note: I think that feedMeReference(a = 3, a) is the exact same situation as feedMeReference(ra = 3, a). However it seems not everybody agrees, in the addition to having 2 completely different answers.

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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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