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• NULL pointer comparison fails

  - by Ilya

  Hello, I'm initializing in a class a pointer to be NULL. Afterwards I check if it is NULL in the same class. But it's not always 0x0. Sometimes it's 0x8 or 0xfeffffff or 0x3f800000 or 0x80 or other strange stuff. In most case the pointer is 0x0 but sometimes it gets altered somehow. I'm sure that I'm not changing it anywhere in my code. Is there a way it gets changed by "itself"? Here's my code: MeshObject::MeshObject() { mesh.vertexColors = NULL; } MeshObject::MeshObject(const MeshObject &_copyFromMe) { SimpleLog("vertexColors pointer: %p", _copyFromMe.mesh.vertexColors); if (_copyFromMe.mesh.vertexColors != NULL) { SimpleLog("vertexColors"); this->mesh.vertexColors = new tColor4i[_copyFromMe.mesh.vertexCount]; memcpy(this->mesh.vertexColors, _copyFromMe.mesh.vertexColors, _copyFromMe.mesh.vertexCount * sizeof(tColor4i) ); } } My application crashes, because vertexColors wasn't initialized and is being copied. However it is NULL and shouldn't be copied. Thanks.

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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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• Visual studio 2008 unit test keeps failing

  - by Gerbrand

  I've create a method that calculates the harmonic mean based on a list of doubles. But when I'm running the test it keeps failing even thou the output result are the same. My harmonic mean method: public static double GetHarmonicMean(List<double> parameters) { var cumReciprocal = 0.0d; var countN = parameters.Count; foreach( var param in parameters) { cumReciprocal += 1.0d/param; } return 1.0d/(cumReciprocal/countN); } My test method: [TestMethod()] public void GetHarmonicMeanTest() { var parameters = new List<double> { 1.5d, 2.3d, 2.9d, 1.9d, 5.6d }; const double expected = 2.32432293165495; var actual = OwnFunctions.GetHarmonicMean(parameters); Assert.AreEqual(expected, actual); } After running the test the following message is showing: Assert.AreEqual failed. Expected:<2.32432293165495. Actual:<2.32432293165495. For me that are both the same values. Can somebody explain this? Or am I doing something wrong?

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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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• C Static Function Confusion

  - by Lime

  I am trying to make the s_cord_print function visible in the cord_s.c file only. Currently the function is visible/runnable in main.c even when it is declared static. How do I make the s_cord_print function private to cord_s.c? Thanks! s_cord.c typedef struct s_cord{ int x; int y; struct s_cord (*print)(); } s_cord; void* VOID_THIS; #define $(EL) VOID_THIS=&EL;EL static s_cord s_cord_print(){ struct s_cord *THIS; THIS = VOID_THIS; printf("(%d,%d)\n",THIS->x,THIS->y); return *THIS; } const s_cord s_cord_default = {1,2,s_cord_print}; main.c #include <stdio.h> #include <stdlib.h> #include "s_cord.c" int main(){ s_cord mycord = s_cord_default; mycord.x = 2; mycord.y = 3; $(mycord).print().print(); //static didn't seem to hide the function s_cord_print(); return 0; } ~

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• C++ template and pointers

  - by Kary

  I have a problem with a template and pointers ( I think ). Below is the part of my code: /* ItemCollection.h */ #ifndef ITEMCOLLECTION_H #define ITEMCOLLECTION_H #include <cstddef> using namespace std; template <class T> class ItemCollection { public: // constructor //destructor void insertItem( const T ); private: struct Item { T price; Item* left; Item* right; }; Item* root; Item* insert( T, Item* ); }; #endif And the file with function defintion: /* ItemCollectionTemp.h-member functions defintion */ #include <iostream> #include <cstddef> #include "ItemCollection.h" template <class Type> Item* ItemCollection <T>::insert( T p, Item* ptr) { // function body } Here are the errors which are generated by this line of code: Item* ItemCollection <T>::insert( T p, Item* ptr) Errors: error C2143: syntax error : missing ';' before '*' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2065: 'Type' : undeclared identifier error C2065: 'Type' : undeclared identifier error C2146: syntax error : missing ')' before identifier 'p' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2470: 'ItemCollection::insert' : looks like a function definition, but there is no parameter list; skipping apparent body error C2072: 'ItemCollection::insert': initialization of a function error C2059: syntax error : ')' Any help is much appreciated.

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• Functions and arrays

  - by Ordo

  Hello! My little program below shall take 5 numbers from the user, store them into an array of integers and use a function to print them out. Sincerly it doesn't work and nothing is printed out. I can't find a mistake, so i would be glad about any advice. Thanks. #include <stdio.h> void printarray(int intarray[], int n) { int i; for(i = 0; i < n; i ++) { printf("%d", intarray[i]); } } int main () { const int n = 5; int temp = 0; int i; int intarray [n]; char check; printf("Please type in your numbers!\n"); for(i = 0; i < n; i ++) { printf(""); scanf("%d", &temp); intarray[i] = temp; } printf("Do you want to print them out? (yes/no): "); scanf("%c", &check); if (check == 'y') printarray(intarray, n); getchar(); getchar(); getchar(); getchar(); return 0; }

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• And now for a complete change of direction from C++ function pointers

  - by David

  I am building a part of a simulator. We are building off of a legacy simulator, but going in different direction, incorporating live bits along side of the simulated bits. The piece I am working on has to, effectively route commands from the central controller to the various bits. In the legacy code, there is a const array populated with an enumerated type. A command comes in, it is looked up in the table, then shipped off to a switch statement keyed by the enumerated type. The type enumeration has a choice VALID_BUT_NOT_SIMULATED, which is effectively a no-op from the point of the sim. I need to turn those no-ops into commands to actual other things [new simulated bits| live bits]. The new stuff and the live stuff have different interfaces than the old stuff [which makes me laugh about the shill job that it took to make it all happen, but that is a topic for a different discussion]. I like the array because it is a very apt description of the live thing this chunk is simulating [latching circuits by row and column]. I thought that I would try to replace the enumerated types in the array with pointers to functions and call them directly. This would be in lieu of the lookup+switch.

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• Optimizing C++ Tree Generation

  - by cam

  Hi, I'm generating a Tic-Tac-Toe game tree (9 seconds after the first move), and I'm told it should take only a few milliseconds. So I'm trying to optimize it, I ran it through CodeAnalyst and these are the top 5 calls being made (I used bitsets to represent the Tic-Tac-Toe board): std::_Iterator_base::_Orphan_me std::bitset<9::test std::_Iterator_base::_Adopt std::bitset<9::reference::operator bool std::_Iterator_base::~_Iterator_base void BuildTreeToDepth(Node &nNode, const int& nextPlayer, int depth) { if (depth > 0) { //Calculate gameboard states int evalBoard = nNode.m_board.CalculateBoardState(); bool isFinished = nNode.m_board.isFinished(); if (isFinished || (nNode.m_board.isWinner() > 0)) { nNode.m_winCount = evalBoard; } else { Ticboard tBoard = nNode.m_board; do { int validMove = tBoard.FirstValidMove(); if (validMove != -1) { Node f; Ticboard tempBoard = nNode.m_board; tempBoard.Move(validMove, nextPlayer); tBoard.Move(validMove, nextPlayer); f.m_board = tempBoard; f.m_winCount = 0; f.m_Move = validMove; int currPlay = (nextPlayer == 1 ? 2 : 1); BuildTreeToDepth(f,currPlay, depth - 1); nNode.m_winCount += f.m_board.CalculateBoardState(); nNode.m_branches.push_back(f); } else { break; } }while(true); } } } Where should I be looking to optimize it? How should I optimize these 5 calls (I don't recognize them=.

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• Why my linux signal handler run only once

  - by Henry Fané

  #include <iostream> #include <signal.h> #include <fenv.h> #include <string.h> void signal_handler(int sig, siginfo_t *siginfo, void* context) { std::cout << " signal_handler " << fetestexcept(FE_ALL_EXCEPT) << std::endl; throw "exception"; } void divide() { float a = 1000., b = 0., c, f = 1e-300; c = a / b; std::cout << c << " and f = " << f << std::endl; } void init_sig_hanlder() { feenableexcept(FE_ALL_EXCEPT); struct sigaction sa, initial_sa; sa.sa_sigaction = &signal_handler ; sigemptyset( &sa.sa_mask ) ; sa.sa_flags = SA_SIGINFO; // man sigaction(3) // allows for void(*)(int,siginfo_t*,void*) handler sigaction(SIGFPE, &sa, &initial_sa); } int main(int argc, char** argv) { init_sig_hanlder(); while(true) { try { sleep(1); divide(); } catch(const char * a) { std::cout << "Exception in catch: " << a << std::endl; } catch(...) { std::cout << "Exception in ..." << std::endl; } } return 0; } Produce the following results on Linux/g++4.2: signal_handler 0 Exception in catch: exception inf and f = 0 inf and f = 0 inf and f = 0 inf and f = 0 So, signal handler is executed the first time but the next fp exception does not trigger the handler again. Where am I wrong ?

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• C++ Design Question on template types

  - by user231536

  I have a templated class template <typename T> class MyContainerClass For types to be substituted for T, it has to satisfy many requirements: for example, get_id(), int data(), etc. Obviously none of the fundamental types (PODs) are substitutable. One way I can provide this is via wrappers for the PODs that provide these functions. Is this an acceptable way? Another way would be to change the template to: template < typename T, typename C=traits<T> > class MyContainerClass and inside MyContainerClass, call traits::data() instead of data() on T objects. I will specialize traits<int>, traits<const char *> etc. Is this good design ? How do I design such a traits class (completely static methods or allow for inheritance) ? Or are the wrapper classes a good solution? What other alternatives are there?

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• MVC Validator.TryValidateObject does not validate custom atrribute, validateAllProperties = true

  - by nealsu

  When calling Validator.TryValidateObject with validateAllProperties = true my custom validation attribute does not get triggered. The ValidationResult does not contain an entry for my erroneous property value. Below is the model, attribute and code used to test this. //Model public class Model { [AmountGreaterThanZero] public int? Amount { get; set; } } //Attribute public sealed class AmountGreaterThanZero: ValidationAttribute { private const string errorMessage = "Amount should be greater than zero."; public AmountGreaterThanZero() : base(errorMessage) { } public override string FormatErrorMessage(string name) { return errorMessage; } protected override ValidationResult IsValid(object value, ValidationContext validationContext) { if (value != null) { if ((int)value <= 0) { var message = FormatErrorMessage(validationContext.DisplayName); return new ValidationResult(message); } } return null; } } //Validation Code var container = new Container(); container.ModelList = new List<Model>() { new Model() { Amount = -5 } }; var validationContext = new ValidationContext(container, null, null); var validationResults = new List<ValidationResult>(); var modelIsValid = Validator.TryValidateObject(container, validationContext, validationResults, true); Note: That the validation works fine and ValidationResult returns with correct error message if I use the TryValidateProperty method.

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• Sha256 is giving junk output

  - by user1746617

  hey can u be more specific on how to convert to bin to hex. bool HashStatus::calculate_digest_value(char * path,unsigned char * output) { FILE* file = fopen(path, "rb"); if(!file) { g_message("SignatureValidator::VerifyReferences,file not opened"); return -1; } unsigned char hash[SHA256_DIGEST_LENGTH]; SHA256_CTX sha256; SHA256_Init(&sha256); const int bufSize = 32768; unsigned char* buffer = malloc(bufSize); int bytesRead = 0; if(!buffer) return NULL; while((bytesRead = fread(buffer, 1, bufSize, file))) { g_message("calculate digest value,verify.cpp::%s",buffer); SHA256_Update(&sha256, buffer, bytesRead); } SHA256_Final(hash, &sha256); g_message("verify.cpp,after final"); sha256_hash_string(hash, output); g_message("verify.cpp,after sha256_hash_string %s",hash); fclose(file); free(buffer); return true; } this is my code to convert file data into hash using sha256 openssl function o/p is :1d54e12333988471354907a760b9cde861423615bb5255ee837e3b27b32366 but actual o/p is:HVThAjM5iEcTVJB6dgC5zehhQjYVu1JV7oN+OyezI2Y= can you guys please help me with whatz wrong with this code,ASAP and i'm new to this please guide me step by step and in detail..

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• C++ STL question related to insert iterators and sets

  - by rshepherd

  #include #include #include #include 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 typical STL style 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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• [gtk+] run function in another thread than gui

  - by sterh

  Hello, I have simple C/gtk+ application. I have function in this app which load image in gtkimageview widget: gboolean main_win_open( MainWin* mw, const char* file_path) { ... //loading and displaing image in gtkimageview ... } The loading image is work, but i need to run this function in another thread then main gui form; I have function: void* argument_thread(void *args) { Data *data = (Data*)args; gdk_threads_enter(); main_win_open (data->win,data->argv); gdk_threads_leave(); } Data it's structure for main_win_open function arguments: typedef struct _Data { MainWin *win; char* argv; } Data; Then in main function i create thread and run it: int main(int argc, char** argv) { GError* err; GThread* thread; Data data; MainWin *win; // init thread support if(!g_thread_supported()) g_thread_init(NULL); gdk_threads_init(); // init GTK+ gtk_init (&argc, &argv); win = (MainWin*)main_win_new(); gtk_widget_show(GTK_WIDGET(win)); data.win = win; data.argv = argv[1]; if (argc == 2) { thread = g_thread_create((GThreadFunc)argument_thread,&data,FALSE, &err); } gdk_threads_enter(); gtk_main(); gdk_threads_leave(); } But when i try to run app from command line and try to load big-size image, gui is blocking. What's wrong? Thank you.

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• How to negate a predicate function using operator ! in C++?

  - by Chan

  Hi, I want to erase all the elements that do not satisfy a criterion. For example: delete all the characters in a string that are not digit. My solution using boost::is_digit worked well. struct my_is_digit { bool operator()( char c ) const { return c >= '0' && c <= '9'; } }; int main() { string s( "1a2b3c4d" ); s.erase( remove_if( s.begin(), s.end(), !boost::is_digit() ), s.end() ); s.erase( remove_if( s.begin(), s.end(), !my_is_digit() ), s.end() ); cout << s << endl; return 0; } Then I tried my own version, the compiler complained :( error C2675: unary '!' : 'my_is_digit' does not define this operator or a conversion to a type acceptable to the predefined operator I could use not1() adapter, however I still think the operator ! is more meaningful in my current context. How could I implement such a ! like boost::is_digit() ? Any idea? Thanks, Chan Nguyen

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• SFINAE and detecting if a C++ function object returns void.

  - by Tom Swirly

  I've read the various authorities on this, include Dewhurst and yet haven't managed to get anywhere with this seemingly simple question. What I want to do is to call a C++ function object, (basically, anything you can call, a pure function or a class with ()), and return its value, if that is not void, or "true" otherwise. #include <stdio.h> struct Foo { void operator()() {} }; struct Bar { bool operator()() { return false; } }; Foo foo; Bar bar; bool baz() { return false; } void bang() {} const char* print(bool b) { printf(b ? "true, " : "false, "); } template <typename Functor> bool magicCallFunction(Functor f) { return true; // lots of template magic occurs here... } int main(int argc, char** argv) { print(magicCallFunction(foo)); print(magicCallFunction(bar)); print(magicCallFunction(baz)); print(magicCallFunction(bang)); printf("\n"); }

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• Inexplicably slow query in MySQL

  - by Brandon M.

  Given this result-set: mysql> EXPLAIN SELECT c.cust_name, SUM(l.line_subtotal) FROM customer c -> JOIN slip s ON s.cust_id = c.cust_id -> JOIN line l ON l.slip_id = s.slip_id -> JOIN vendor v ON v.vend_id = l.vend_id WHERE v.vend_name = 'blahblah' -> GROUP BY c.cust_name -> HAVING SUM(l.line_subtotal) > 49999 -> ORDER BY c.cust_name; +----+-------------+-------+--------+---------------------------------+---------------+---------+----------------------+------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+---------------------------------+---------------+---------+----------------------+------+----------------------------------------------+ | 1 | SIMPLE | v | ref | PRIMARY,idx_vend_name | idx_vend_name | 12 | const | 1 | Using where; Using temporary; Using filesort | | 1 | SIMPLE | l | ref | idx_vend_id | idx_vend_id | 4 | csv_import.v.vend_id | 446 | | | 1 | SIMPLE | s | eq_ref | PRIMARY,idx_cust_id,idx_slip_id | PRIMARY | 4 | csv_import.l.slip_id | 1 | | | 1 | SIMPLE | c | eq_ref | PRIMARY,cIndex | PRIMARY | 4 | csv_import.s.cust_id | 1 | | +----+-------------+-------+--------+---------------------------------+---------------+---------+----------------------+------+----------------------------------------------+ 4 rows in set (0.04 sec) I'm a bit baffled as to why the query referenced by this EXPLAIN statement is still taking about a minute to execute. Isn't it true that this query only has to search through 449 rows? Anyone have any idea as to what could be slowing it down so much?

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• remove versioning on boost xml serialization

  - by cppanda

  hi, i just can't find a way to remove the version tracking from the boost xmlarchives. example <Settings class_id="0" tracking_level="0" version="1"> <px class_id="1" tracking_level="1" version="0" object_id="_0"> <TestInt>3</TestInt> <Resolution class_id="2" tracking_level="0" version="0"> <x>800</x> <y>600</y> </Resolution> <SomeStuff>0</SomeStuff> </px> </Settings> I want to get ride of the class_id="0" tracking_level="0" version="1" stuff, because for in this case i just don't need it and want a simple clean config like file code void serialize(Archive & ar, const unsigned int version) { ar & make_nvp("TestInt", TestInt); ar & make_nvp("Resolution", resolution); ar & make_nvp("SomeStuff", SomeStuff); } i found boost::serialization::track_never, but nowhere to use it

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• How can I use Qt to get html code of this NCBI page??

  - by user308503

  I'm trying to use Qt to download the html code from the following url: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=nucleotide&cmd=search&term=AB100362 this url will re-direct to www.ncbi.nlm.nih.gov/nuccore/27884304 I try to do it by following way, but I cannot get anything. it works for some webpage such as www.google.com, but not for this NCBI page. is there any way to get this page?? QNetworkReply::NetworkError downloadURL(const QUrl &url, QByteArray &data) { QNetworkAccessManager manager; QNetworkRequest request(url); QNetworkReply *reply = manager.get(request); QEventLoop loop; QObject::connect(reply, SIGNAL(finished()), &loop, SLOT(quit())); loop.exec(); if (reply->error() != QNetworkReply::NoError) { return reply->error(); } data = reply->readAll(); delete reply; return QNetworkReply::NoError; } void GetGi() { int pos; QString sGetFromURL = "http://www.ncbi.nlm.nih.gov/entrez/query.fcgi"; QUrl url(sGetFromURL); url.addQueryItem("db", "nucleotide"); url.addQueryItem("cmd", "search"); url.addQueryItem("term", "AB100362"); QByteArray InfoNCBI; int errorCode = downloadURL(url, InfoNCBI); if (errorCode != 0 ) { QMessageBox::about(0,tr("Internet Error "), tr("Internet Error %1: Failed to connect to NCBI.\t\nPlease check your internect connection.").arg(errorCode)); return "ERROR"; } }

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• Picture.writeToStream() not writing out all bitmaps

  - by quickdraw mcgraw

  I'm using webview.capturePicture() to create a Picture object that contains all the drawing objects for a webpage. I can successfully render this Picture object to a bitmap using the canvas.drawPicture(picture, dst) with no problems. However when I use picture.writeToStream(fos) to serialize the picture object out to file, and then Picture.createFromStream(fis) to read the data back in and create a new picture object, the resultant bitmap when rendered as above is missing any larger images (anything over around 20KB! by observation). This occurs on all the Android OS platforms that I have tested 1.5, 1.6 and 2.1. Looking at the native code for Skia which is the underlying Android graphics library and the output file produced from the picture.writeToStream() I can see how the file format is constructed. I can see that some of the images in this Skia spool file are not being written out (the larger ones), the code that appears to be the problem is in skBitmap.cpp in the method void SkBitmap::flatten(SkFlattenableWriteBuffer& buffer) const; It writes out the bitmap fWidth, fHeight, fRowBytes, FConfig and isOpaque values but then just writes out SERIALIZE_PIXELTYPE_NONE (0). This means that the spool file does not contain any pixel information about the actual image and therefore cannot restore the picture object correctly. Effectively this renders the writeToStream and createFromStream() APIs useless as they do not reliably store and recreate the picture data. Has anybody else seen this behaviour and if so am I using the API incorrectly, can it be worked around, is there an explanation i.e. incomplete API / bug and if so are there any plans for a fix in a future release of Android? Thanks in advance.

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• Summary statistics in visual basic

  - by ben

  Below I am trying to write a script the goal of which is to calculate some summary statistics for a few different columns of numbers. I have gotten some help on it up to the "Need help below" mark. But beyond that I am flabergasted as to how to calculate the simple stats (sum, mean, standard deviation, coefficient of variation). I know VB has scripts for these stats, which I have included in my code, but I guess I need to do some extra declaring or something. Advice much appreciated. Thanks. Sub TOAinput() Const n As Integer = 648 Dim stratum(n), hybrid(n), acres(n), hhsz(n), offinc(n) Dim s1 As Integer Dim s2 As Integer Dim i As Integer For i = 1 To n stratum(i) = Worksheets("hhid level").Cells(i + 1, 2).Value Next i s1 = 0 s2 = 0 For i = 1 To n If stratum(i) = 1 Then s1 = s1 + 1 Else: s2 = s2 + 1 End If Next i Dim acres1(), hhsz1(), offinc1(), acres2(), hhsz2(), offinc2() ReDim acres1(s1), hhsz1(s1), offinc1(s1), acres2(s2), hhsz2(s2), offinc2(s2) 'data infiles: acres, hh size, off-farm income, For i = 1 To n acres(i) = Worksheets("hhid level").Cells(i + 1, 4).Value hhsz(i) = Worksheets("hhid level").Cells(i + 1, 5).Value offinc(i) = Worksheets("hhid level").Cells(i + 1, 6).Value Next i s1 = 0 s2 = 0 For i = 1 To n If stratum(i) = 1 Then s1 = s1 + 1 acres1(s1) = acres(i) hhsz1(s1) = hhsz(i) offinc1(s1) = offinc(i) Else: s2 = s2 + 1 acres2(s2) = acres(i) hhsz2(s2) = hhsz(i) offinc2(s2) = offinc(i) End If Next i '**************************** 'Need help below '**************************** Dim sumac1, sumac2, mhhsz1, mhhsz2, cvhhsz1, cvhhsz2 sumac1 = Sum(acres1) sumac2 = Sum(acres2) mhhsz1 = Average(hhsz1) mhhsz2 = Average(hhsz2) cvhhsz1 = StDev(hhsz1) / Average(hhsz1) cvhhsz2 = StDev(hhsz2) / Average(hhsz2) End Sub

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• Using new (this) to reuse constructors

  - by Brandon Bodnar

  This came up recently in a class for which I am a teaching assistant. We were teaching the students how to do copy constructors in c++, and the students who were originally taught java asked if you can call one constructor from another. I know the answer to this is no, as they are using the pedantic flag for their code in class, and the old standards do not have support for this. I found on Stackoverflow and other sites a suggestion to fake this using new (this) such as follows class MyClass { private: int * storedValue; public: MyClass(int initialValue = 0) { storedValue = new int(initialValue); } ~ MyClass() { delete storedValue; } MyClass(const MyClass &b) { new (this) MyClass(*(b.storedValue)); } int value() { return *storedValue; } }; This is really simple code, and obviously does not save any code by reusing the constructor, but it is just for example. My question is if this is even standard compliant, and if there are any edge cases that should be considered that would prevent this from being sound code?

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• Memory allocation patterns in C++

  - by Mahatma

  I am confused about the memory allocation in C++ in terms of the memory areas such as Const data area, Stack, Heap, Freestore, Heap and Global/Static area. I would like to understand the memory allocation pattern in the following snippet. Can anyone help me to understand this. If there any thing more apart from the variable types mentioned in the example to help understand the concept better please alter the example. class FooBar { int n; //Stored in stack? public: int pubVar; //stored in stack? void foo(int param) //param stored in stack { int *pp = new int; //int is allocated on heap. n = param; static int nStat; //Stored in static area of memory int nLoc; //stored in stack? string str = "mystring"; //stored in stack? .. if(CONDITION) { static int nSIf; //stored in static area of memory int loopvar; //stored in stack .. } } } int main(int) { Foobar bar; //bar stored in stack? or a part of it? Foobar *pBar; //pBar is stored in stack pBar = new Foobar(); //the object is created in heap? What part of the object is stored on heap } EDIT: What confuses me is, if pBar = new Foobar(); stores the object on the heap, how come int nLoc; and int pubVar;, that are components of the object stored on stack? Sounds contradictory to me. Shouldn't the lifetime of pubvar and pBar be the same?

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• Copy object using pointer (templates)

  - by Azodious

  How the push_back of stl::vector is implemented so it can make copy of any datatype .. may be pointer, double pointer and so on ... I'm implementing a template class having a function push_back almost similar to vector. Within this method a copy of argument should be inserted in internal memory allocated memory. but the argument is a pointer. (an object pointer). Can you pls tell how to create copy from pointer. so that if i delete the pointer in caller still the copy exists in my template class? Code base is as follows: template<typename T> class Vector { public: void push_back(const T& val_in) { T* a = *(new T(val_in)); m_pData[SIZE++] = a; } } Caller: Vector<MyClass*> v(3); MyClass* a = new MyClass(); a->a = 0; a->b = .5; v.push_back(a); delete a; Thanks.

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