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• Why is joining two vectors simply not working?

  - by Jim

  I have two vectors of MyObj structs. MyObj is defined as follows: struct MyObj { float x, y; unsigned int data[8]; unsigned int tmp[1]; MyObj(const MyObj &m) { x = m.x; y = m.y; tmp[0] = 0; for (int i = 0; i < 8; ++i) { data[i] = m.data[i]; } } }; I then have two vectors... vector<MyObj> v1; vector<MyObj> v2; // both get data eventually. v1.insert(v1.end(), v2.begin(), v2.end()); v2 has 3535004 elements in my experiment. v1 is similarly sized. I've also tried building a new vector and just using .push_back to build it from both vectors. Essentially, when I try to merge the two vectors I just get an error from visual studio saying "Debug error! R6010, abort() has been called". Very non-useful... So my question is: what could be causing this error, and how can I solve it? Thank you

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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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• is there a simple timed lock algorithm avoiding deadlock on multiple mutexes?

  - by Vicente Botet Escriba

  C++0x thread library or Boost.thread define a non-member variadic template function that locks all mutex at once that helps to avoid deadlock. template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...); The same can be applied to a non-member variadic template function try_lock_until, which locks all the mutex until a given time is reached that helps to avoid deadlock like lock(...). template <class Clock, class Duration, class L1, class L2, class... L3> void try_lock_until( const chrono::time_point<Clock,Duration>& abs_time, L1&, L2&, L3&...); I have an implementation that follows the same design as the Boost function boost::lock(...). But this is quite complex. As I can be missing something evident I wanted to know if: is there a simple timed lock algorithm avoiding deadlock on multiple mutexes? If no simple implementation exists, can this justify a proposal to Boost? P.S. Please avoid posting complex solutions.

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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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• 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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• C++ - Where to throw exception?

  - by HardCoder1986

  Hello! I have some kind of an ideological question, so: Suppose I have some templated function template <typename Stream> void Foo(Stream& stream, Object& object) { ... } which does something with this object and the stream (for example, serializes that object to the stream or something like that). Let's say I also add some plain wrappers like (and let's say the number of these wrappers equals 2 or 3): void FooToFile(const std::string& filename, Object& object) { std::ifstream stream(filename.c_str()); Foo(stream, object); } So, my question is: Where in this case (ideologically) should I throw the exception if my stream is bad? Should I do this in each wrapper or just move that check to my Foo, so that it's body would look like if (!foo.good()) throw (something); // Perform ordinary actions I understand that this may be not the most important part of coding and these solutions are actually equal, but I just wan't to know "the proper" way to implement this. Thank you.

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• How to know the type of an object in a list?

  - by nacho4d

  Hi, I want to know the type of object (or type) I have in my list so I wrote this: void **list; //list of references list = new void * [2]; Foo foo = Foo(); const char *not_table [] = {"tf", "ft", 0 }; list[0] = &foo; list[1] = not_table; if (dynamic_cast<LogicProcessor*>(list[0])) { //ERROR here ;( printf("Foo was found\n"); } if (dynamic_cast<char*> (list[0])) { //ERROR here ;( printf("char was found\n"); } but I get : error: cannot dynamic_cast '* list' (of type 'void*') to type 'class Foo*' (source is not a pointer to class) error: cannot dynamic_cast '* list' (of type 'void*') to type 'char*' (target is not pointer or reference to class) Why is this? what I am doing wrong here? Is dynamic_cast what I should use here? Thanks in advance EDIT: I know above code is much like plain C and surely sucks from the C++ point of view but is just I have the following situation and I was trying something before really implementing it: I have two arrays of length n but both arrays will never have an object at the same index. Hence, or I have array1[i]!=NULL or array2[i]!=NULL. This is obviously a waste of memory so I thought everything would be solved if I could have both kind of objects in a single array of length n. I am looking something like Cocoa's (Objective-C) NSArray where you don't care about the type of the object to be put in. Not knowing the type of the object is not a problem since you can use other method to get the class of a certain later. Is there something like it in c++ (preferably not third party C++ libraries) ? Thanks in advance ;)

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• loading record into detailview

  - by summer

  please please i need help..i think i am lost somewhere..basically i followed the example http://www.iphonesdkarticles.com/2008/10/sqlite-tutorial-loading-data-as.html, but i was stuck with error on reading description..something must had gone wrong some well but i am not very sure how should i solve it. this is my code, actually i dun really have an idea on wat's really going in this code..help please..2days!! no solution!! - (void) hydrateDetailViewData { //if detail view is hydrated then do not get it from database if(isDetailViewHydrated) return; if(detailStmt == nil) { const char *sql = "select snapTitle, snapDesc from Snap where snapID =?"; if(sqlite3_prepare_v2(database, sql, -1, &detailStmt, NULL) != SQLITE_OK) NSAssert1(0, @"Error while creating detail view statement. '%s'", sqlite3_errmsg(database)); NSLog(@"SQLite= %d", sqlite3_step(detailStmt)); } if(SQLITE_DONE != sqlite3_step(detailStmt)) { // NSString *descStr = [[NSString alloc] //initWithString:sqlite3_column_text(detailStmt, 2)]; NSString *descStr = [NSString stringWithUTF8String:(char *)sqlite3_column_text(detailStmt,2)]; self.snapDescription = descStr; [descStr release]; } else NSAssert1(0, @"Error getting description of snap2play. '%s'", sqlite3_errmsg(database)); sqlite3_reset(detailStmt); isDetailViewHydrated = YES; //if hydrated, make sure do not get from database again. } }

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• Changing file permissions in kernel.

  - by Mehrdad

  I am writing kernel module(C in Linux) and I want to change the permission of the other files in it. any solution? since I am in kernel I can't use chmod syscall and ... thanks for your help This is my Makefile: > obj-m += ca.o > > all: > make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules > > clean: > make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean And this is my Code: > #include <linux/string.h> > #include <linux/mm.h> > /* Snip, tons of includes (all of them :))*/ > #include <linux/delay.h> .... int procfile_write(struct file *file, > const char *buffer, unsigned long > count, > void *data) { ... sys_chmod(path, per); ... } ... When Making it gives a warning: WARNING: "sys_chmod" [file] undefiened and when loading the module with "sudo insmod" it gives this error: Unknown sybol in module it seems that this error happens especialy in kernel modules. any idea? again thanks!

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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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• Placing and removing element on array trough object

  - by Chris

  Hello, Lets assume i have 2 methods 1 that places a element on the array and one that removes it. const int Max = 10; int[] table= new int[Max]; I would like to call it up like this: s1.Place(5); // 5 0 0 0 0 0 0 0 0 0 0 s1.Place(9); // 5 9 0 0 0 0 0 0 0 0 0 s1.Remove(9); // 5 0 0 0 0 0 0 0 0 0 0 I would only like to use : using system for this. The result i get right now when i run the program is s1 = "nameofprogram" "name of class object" Normally i should get 0 0 0 0 0 0 0 0 0 0 to begin with. Any ideas how i can exactly add or remove those elements on the array? public void Place(int g) { if (top == Max) { throw new Exception("Stack overflow..."); } else { table[top] = g; top++; } .... Best Regards.

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• C++: Trouble with dependent types in templates

  - by Rosarch

  I'm having trouble with templates and dependent types: namespace Utils { void PrintLine(const string& line, int tabLevel = 0); string getTabs(int tabLevel); template<class result_t, class Predicate> set<result_t> findAll_if(typename set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred) // warning C4346 { set<result_t> result; return findAll_if_rec(begin, end, pred, result); } } namespace detail { template<class result_t, class Predicate> set<result_t> findAll_if_rec(set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred, set<result_t> result) { typename set<result_t>::iterator nextResultElem = find_if(begin, end, pred); if (nextResultElem == end) { return result; } result.add(*nextResultElem); return findAll_if_rec(++nextResultElem, end, pred, result); } } Compiler complaints, from the location noted above: warning C4346: 'std::set<result_t>::iterator' : dependent name is not a type. prefix with 'typename' to indicate a type error C2061: syntax error : identifier 'iterator' What am I doing wrong?

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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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• C++ : Declaring the array size with a non-constant variable

  - by Jérôme

  I always thought that when declaring an array in C++, the size has to be a constant integer value. For instance : int MyArray[5]; // correct or const int ARRAY_SIZE = 6; int MyArray[ARRAY_SIZE]; // correct but int ArraySize = 5; int MyArray[ArraySize]; // incorrect Here is also what is explained in The C++ Programming Language, by Bjarne Stroustrup : The number of elements of the array, the array bound, must be a constant expression (§C.5). If you need variable bounds, use a vector(§3.7.1, §16.3). For example: void f(int i) { int v1[i]; // error : array size not a constant expression vector<int> v2[i]; // ok } But to my big surprise, the code above does compile fine on my system ! Here is what I tried to compile : void f(int i) { int v2[i]; } int main() { int i = 3; int v1[i]; f(5); } I got no error ! I'm using GCC v4.4.0. Is there something I'm missing ?

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• SQLite3 - select date range not working

  - by iFloh

  yet anotherone that gives me grief. In a SQLite3 DB Select I query for a date range specified in (NSDate *)fromDate to (NSDate *)toDate const char *sql = "SELECT * FROM A, B WHERE A.key = B.key AND A.date between ? and ?"; After opening the DB I run the query in Objective-C as follows: NSDateFormatter *tmpDatFmt = [[[NSDateFormatter alloc] init] autorelease]; [tmpDatFmt setDateFormat:@"dd-MM-yyyy"]; sqlite3_stmt *stmt; if(sqlite3_prepare_v2(db, sql, -1, &stmt, NULL) == SQLITE_OK) { NSLog(@"From %s to %s;", [[tmpDatFmt stringFromDate:fromDate] UTF8String], [[tmpDatFmt stringFromDate:toDate] UTF8String]); sqlite3_bind_text(stmt, 1, [[tmpDatFmt stringFromDate:fromDate] UTF8String], -1, SQLITE_STATIC); // first '?' sqlite3_bind_text(stmt, 2, [[tmpDatFmt stringFromDate:toDate] UTF8String], -1, SQLITE_STATIC); // second '?' while(sqlite3_step(stmt) == SQLITE_ROW) { NSLog(@"Success");} In the database I have several records that match the date range: 12-04-2010 = in seconds 1271059200 13-04-2010 = in seconds 1271145600 13-04-2010 = in seconds 1271152800 14-04-2010 = in seconds 1271267100 When I run it the first NSLog shows From 2010-04-01 to 2010-04-30 my problem is the records are not selected (no "Success" shows in the log) and I don't understand why. earlier I had miscalculated the dates 2 days later as 14-04-2010 = in seconds 1271232000 15-04-2010 = in seconds 1271318400 15-04-2010 = in seconds 1271325600 16-04-2010 = in seconds 1271439936 These dates worked fine (4 x "Success in the log). I am puzzled ...

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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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• CArray doesn't call copy constructors on memory reallocations, now what?

  - by MMx

  Suppose I have a class that requires copy constructor to be called to make a correct copy of: struct CWeird { CWeird() { number = 47; target = &number; } CWeird(const CWeird &other) : number(other.number), target(&number) { } void output() { printf("%d %d\n", *target, number); } int *target, number; }; Now the trouble is that CArray doesn't call copy constructors on its elements when reallocating memory (only memcpy from the old memory to the new), e.g. this code CArray<CWeird> a; a.SetSize(1); a[0].output(); a.SetSize(2); a[0].output(); results in 47 47 -572662307 47 I don't get this. Why is it that std::vector can copy the same objects properly and CArray can't? What's the lesson here? Should I use only classes that don't require explicit copy constructors? Or is it a bad idea to use CArray for anything serious?

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• What is the point of having a key_t if what will be the key to access shared memory is the return value of shmget()?

  - by devoured elysium

  When using shared memory, why should we care about creating a key key_t ftok(const char *path, int id); in the following bit of code? key_t key; int shmid; key = ftok("/home/beej/somefile3", 'R'); shmid = shmget(key, 1024, 0644 | IPC_CREAT); From what I've come to understand, what is needed to access a given shared memory is the shmid, not the key. Or am I wrong? If what we need is the shmid, what is the point in not just creating a random key every time? Edit @link text one can read: What about this key nonsense? How do we create one? Well, since the type key_t is actually just a long, you can use any number you want. But what if you hard-code the number and some other unrelated program hardcodes the same number but wants another queue? The solution is to use the ftok() function which generates a key from two arguments. Reading this, it gives me the impression that what one needs to attach to a shared-memory block is the key. But this isn't true, is it? Thanks

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• destructor being called by subclass

  - by zero

  I'm currently learning more about php objects and constructors/destructors, but i've noticed in my code that the parent class's destructor is being called twice, I thought it was because i was extending the first class to my second class and that the second class was calling it, but this is what the php docs say about that: Like constructors, parent destructors will not be called implicitly by the engine. In order to run a parent destructor, one would have to explicitly call parent::__destruct() in the destructor body. so if it is not being called by the subclass then is it because by extended the first class that i've made a reference to the parent class making it call itself twice or I'm I way off base here? the code: <?php class test{ public $test1 = "this is a test of a pulic property"; private $test2 = "this is a test of a private property"; protected $test3 = "this is a test of a protected property"; const hello = 900000; function __construct($h){ //echo 'this is the constructor test '.$h; } function x($x2){ echo ' this is fn x'.$x2; } function y(){ print "this is fn y"; } } $obj = new test("this is an \"arg\" sent to instance of test"); class hey extends test{ function hey(){ $this->x('<br>from the host with the most'); echo ' <br>from hey class'.$this->test3; } } $obj2 = new hey(); echo $obj2::hello; ?>

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• Is this an error in "More Effective C++" in Item28?

  - by particle128

  I encountered a question when I was reading the item28 in More Effective C++ .In this item, the author shows to us that we can use member template in SmartPtr such that the SmartPtr<Cassette> can be converted to SmartPtr<MusicProduct>. The following code is not the same as in the book,but has the same effect. #include <iostream> class Base{}; class Derived:public Base{}; template<typename T> class smart{ public: smart(T* ptr):ptr(ptr){} template<typename U> operator smart<U>() { return smart<U>(ptr); } ~smart(){delete ptr;} private: T* ptr; }; void test(const smart<Base>& ) {} int main() { smart<Derived> sd(new Derived); test(sd); return 0; } It indeed can be compiled without compilation error. But when I ran the executable file, I got a core dump. I think that's because the member function of the conversion operator makes a temporary smart, which has a pointer to the same ptr in sd (its type is smart<Derived>). So the delete directive operates twice. What's more, after calling test, we can never use sd any more, since ptr in sd has already been delete. Now my questions are : Is my thought right? Or my code is not the same as the original code in the book? If my thought is right, is there any method to do this? Thanks very much for your help.

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• std::thread and class constructor and destructor

  - by toeplitz

  When testing threads in C++11 I have created the following example: #include <iostream> #include <thread> class Foo { public: Foo(void) { std::cout << "Constructor called: " << this << std::endl; } ~Foo(void) { std::cout << "Destructor called: " << this << std::endl; } void operator()() const { std::cout << "Operatior called: " << this << std::endl; } }; void test_normal(void) { std::cout << "====> Standard example:" << std::endl; Foo f; } void test_thread(void) { std::cout << "====> Thread example:" << std::endl; Foo f; std::thread t(f); t.detach(); } int main(int argc, char **argv) { test_normal(); test_thread(); for(;;); } Which prints the following: Why is the destructor called 6 times for the thread? And why does the thread report different memory locations?

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• base class , inheritate class sizeof()

  - by user1279988

  why sizeof(X) is 4 and sizeof(Y) is 8? and another question, in class X, only the int(i) count as sizeof() 4? member function does take any memory space? Plz tell me, thanks! class X { int i; public: X() { i = 0; } void set(int ii) { i = ii; } int read() const { return i; } int permute() { return i = i * 47; } }; class Y : public X { int i; // Different from X's i public: Y() { i = 0; } int change() { i = permute(); // Different name call return i; } void set(int ii) { i = ii; X::set(ii); // Same-name function call } }; cout << "sizeof(X) = " << sizeof(X) << endl; cout << "sizeof(Y) = "

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• Why this doesnt't work in C++?

  - by user3377450

  I'm doing something and I have this: //main.cpp file template<typename t1, typename t2> std::ostream& operator<<(std::ostream& os, const std::pair<t1, t2>& pair) { return os << "< " << pair.first << " , " << pair.second << " >"; } int main() { std::map<int, int> map = { { 1, 2 }, { 2, 3 } }; std::cout << *map.begin() << std::endl;//This works std::copy(map.begin(), map.end(), std::ostream_iterator<std::pair<int,int> >(std::cout, " "));//this doesn't work } I guess this is not working because in the std::copy algorithm the operator isn't defined, but what can I do?

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• Optimal (Time paradigm) solution to check variable within boundary

  - by kumar_m_kiran

  Hi All, Sorry if the question is very naive. I will have to check the below condition in my code 0 < x < y i.e code similar to if(x > 0 && x < y) The basic problem at system level is - currently, for every call (Telecom domain terminology), my existing code is hit (many times). So performance is very very critical, Now, I need to add a check for boundary checking (at many location - but different boundary comparison at each location). At very normal level of coding, the above comparison would look very naive without any issue. However, when added over my statistics module (which is dipped many times), performance will go down. So I would like to know the best possible way to handle the above scenario (kind of optimal way for limits checking technique). Like for example, if bit comparison works better than normal comparison or can both the comparison be evaluation in shorter time span? Other Info x is unsigned integer (which must be checked to be greater than 0 and less than y). y is unsigned integer. y is a non-const and varies for every comparison. Here time is the constraint compared to space. Language - C++. Now, later if I need to change the attribute of y to a float/double, would there be another way to optimize the check (i.e will the suggested optimal technique for integer become non-optimal solution when y is changed to float/double). Thanks in advance for any input. PS : OS used is SUSE 10 64 bit x64_64, AIX 5.3 64 bit, HP UX 11.1 A 64.

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• Initialize void pointer to point to an array

  - by idealistikz

  Suppose I have the following: typedef struct { int itemSize; int count; void *list; } Mystruct; Mystruct *InitStruct(int itemSize, int count) { Mystruct *my = malloc(sizeof(Mystruct)); my->itemSize = itemSize; my->count = count; //What is the best way to initialize list? For example: //my->list = malloc(count * sizeof(void *)); OR //my->list = malloc(count * sizeof(itemSize)); } //The following should return a pointer to the element stored at a given index void *Retrieve(const MyStruct *my, int index) { void *item; //What is the best way to return a pointer to the item at the given index from //my->list? } Mystruct is similar to an array and void *list is supposed to store the elements or pointers to the elements. Mystruct *InitStruct is a function that initializes a Mystruct pointer and void *Retrieve is a function that returns a pointer to the element stored at a given index. First, how should I initialize void* list? Should it hold the actual elements or be an array of pointers pointing to the elements? Second, using the void *Retrieve function, how do I return a pointer to the element stored at a given index in my-list?

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