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  • deleting dynamically allocated object that contains vector in C++ STL

    - by kobac
    I have a class class ChartLine{ protected: vector<Point> line; // points connecting the line CString name; //line name for legend CPen pen; //color, size and style properties of the line }; where Point is a structure struct Point{ CString x; double y; }; In main() I dynamically allocate objects of type ChartLine with new operator. If I use delete afterwards, will default destructor ~ChartLine() properly dealocate (or clear) member ChartLine::line(which is vector btw) or I would have to clear that vector in ~ChartLine() manually? Thanks in advance. Cheers.

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  • How to implement copy operator for such C++ structure?

    - by Kabumbus
    So having struct ResultStructure { ResultStructure(const ResultStructure& other) { // copy code in here ? using memcpy ? how??? } ResultStructure& operator=(const ResultStructure& other) { if (this != &other) { // copy code in here ? } return *this } int length; char* ptr; }; How to implement copy? (sorry - I am C++ nube)

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  • c++ Sorting a vector based on values of other vector, or what's faster?

    - by pollux
    Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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  • How to perform DNS query on iOS

    - by yasirmturk
    i want to perform some DNS queries e.g. to get IP records against a specific domain name, i am looking for a preferred way or some useful snippet for this on iOS 3.2+ SDK. thanx in advance part from other snippets i found this code Boolean result; CFHostRef hostRef; NSArray *addresses; NSString *hostname = @"apple.com"; hostRef = CFHostCreateWithName(kCFAllocatorDefault, (CFStringRef)hostname); if (hostRef) { result = CFHostStartInfoResolution(hostRef, kCFHostAddresses, NULL); // pass an error instead of NULL here to find out why it failed if (result == TRUE) { addresses = (NSArray*)CFHostGetAddressing(hostRef, &result); } } if (result == TRUE) { [addresses enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { NSString *strDNS = [NSString stringWithUTF8String:inet_ntoa(*((struct in_addr *)obj))]; NSLog(@"Resolved %d->%@", idx, strDNS); }]; } else { NSLog(@"Not resolved"); } but this is producing same IP for every host Resolved 0-220.120.64.1 any help??

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  • How to bind WPF TreeView to a List<Drink> programmatically?

    - by Joan Venge
    So I am very new to WPF and trying to bind or assign a list of Drink values to a wpf treeview, but don't know how to do that, and find it really hard to find anything online that just shows stuff without using xaml. struct Drink { public string Name { get; private set; } public int Popularity { get; private set; } public Drink ( string name, int popularity ) : this ( ) { this.Name = name; this.Popularity = popularity; } } List<Drink> coldDrinks = new List<Drink> ( ){ new Drink ( "Water", 1 ), new Drink ( "Fanta", 2 ), new Drink ( "Sprite", 3 ), new Drink ( "Coke", 4 ), new Drink ( "Milk", 5 ) }; } } How can I do this in code? For example: treeview1.DataItems = coldDrinks; and everything shows up in the treeview.

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  • WAVEFORMATEX - how to read codecdata at the end??

    - by Roey
    Hi All. I've a WAVEFORMATEX struct with some codecdata at the end of it (10 bytes). I'm using C++. How do I access the data at the end? (this is a purely technical question). I tried : WAVEFORMATEX* wav = (WAVEFORMATEX*)pmt->pbFormat; WORD me = wav->cbSize; wav = wav + sizeof(WAVEFORMATEX); BYTE* arr = new BYTE[me]; memcpy(arr, (BYTE*)wav, me); Didnt work. Thanks Roey

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  • When convert a void pointer to a specific type pointer, which casting symbol is better, static_cast or reinterpret_cast?

    - by BugCreater
    A beginner question with poor English: Here I got a void* param and want to cast(or change) it to a specific type. But I don't know which "casting symbol" to use. Either**static_cast** and reinterpret_cast works. I want to know which one is better? which one does the Standard C++ recommend? typedef struct { int a; }A, *PA; int foo(void* a) // the real type of a is A* { A* pA = static_cast<A*>(a); // or A* pA = reinterpret_cast<A*>(a);? cout<<pA->a<<endl; return 0; } Here I use A* pA = static_cast(a); or A* pA = reinterpret_cast(a); is more proper?

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  • Large amount of constants in Java

    - by Lars D
    I need to include about 1 MByte of data in a Java application, for very fast and easy access in the rest of the source code. My main background is not Java, so my initial idea was to convert the data directly to Java source code, defining 1MByte of constant arrays, classes (instead of C++ struct) etc., something like this: public final/immutable/const MyClass MyList[] = { { 23012, 22, "Hamburger"} , { 28375, 123, "Kieler"} }; However, it seems that Java does not support such constructs. Is this correct? If yes, what is the best solution to this problem?

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  • Arrange 0's & 1's in a array

    - by Ganesh M
    This is one of an interview question which I had recently. I would like to know others perception of approach for this problem. Question: You are given a structure which holds an employee details with two elements as int Deptartment and string Name. struct Employee { string Name; int Dept; } You are given details of N Employees among which there are N/2 employees Dept are 0's and N/2 employees dept are 1's arranged in some random order. You need to sort the employee details based on their Dept value and it should be stable i.e., the order of 1s and 0s in the original record should be maintained. For example, given the following sample data: Name Dept X1 0 X2 1 X3 0 X4 1 X5 0 after sorting the result should be: Name Dept X2 1 X4 1 X1 0 X3 0 X5 0 The algorithm should be stable and the complexity should be o(N), with constant space for additional variables (which means sorting should be done in-place).

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  • Reading a variable messes it up?!?!

    - by EpsilonVector
    We have the following line of code: printf("%d\n", toc->runlist.next); printf("%d\n", toc->runlist.next); These are the definitions: typedef struct thread_overview_control{ int id[NR_UTHREADS]; list_t runlist; int active_counter; int main_thread; int need_resched; } thread_overview_control; thread_overview_control* toc; What I'm trying to do is implement user threads. For some reason the output of the above code at the point where our test run crushes is: 12345678 //some address 0 //NOW IT'S NULL?!?!?! How can this happen?? All we do is read a variable. And the strange thing is, without printf's there are no crashes. What's going on?

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  • What is a good way to simulate O_NOFOLLOW on systems without this flag?

    - by Daniel Trebbien
    I would like to safely be able to simulate open with O_CREAT | O_WRONLY | O_TRUNC | O_NOFOLLOW and O_CREAT | O_WRONLY | O_APPEND | O_NOFOLLOW on systems that do not support O_NOFOLLOW. I can somewhat achieve what I am asking for with: struct stat lst; if (lstat(filename, &lst) != -1 && S_ISLNK(lst.st_mode)) { errno = ELOOP; return -1; } mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; int fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC | O_NOFOLLOW, mode); but then I introduce a race condition and possibly a security problem. I thought about maybe creating a dummy file with only the user being able to write, kind of like touching filename, doing the lstat check, and then using chmod after I finish writing (to correct the file mode bits), but I could be overlooking something major (e.g. if the file at filename exists, is not a regular file, or is already a symbolic link). What do you think?

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  • Why does a non-constant offsetof expression work?

    - by Chris J. Kiick
    Why does this work: #include <sys/types.h> #include <stdio.h> #include <stddef.h> typedef struct x { int a; int b[128]; } x_t; int function(int i) { size_t a; a = offsetof(x_t, b[i]); return a; } int main(int argc, char **argv) { printf("%d\n", function(atoi(argv[1]))); } If I remember the definition of offsetof correctly, it's a compile time construct. Using 'i' as the array index results in a non-constant expression. I don't understand how the compiler can evaluate the expression at compile time. Why isn't this flagged as an error?

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  • how to get stl map to construct/destruct inserted object only once.

    - by Alberto Toglia
    I have found a very prejudicial fact about stl maps. For some reason I cant get objects being inserted in the map to get constructed/destructed only once. Example: struct MyObject{ MyObject(){ cout << "constructor" << endl; } ~MyObject(){ cout << "destructor" << endl; } }; int main() { std::map<int, MyObject> myObjectsMap; myObjectsMap[0] = MyObject(); return 0; } returns: constructor destructor destructor constructor destructor If I do: typedef std::pair<int, MyObject> MyObjectPair; myObjectsMap.insert( MyObjectPair(0,MyObject())); returns: constructor destructor destructor destructor I'm inserting Objects responsible for their own memory allocation, so when destructed they'll clean themselves up, being destructed several times is causing me some trouble.

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  • Can the template parameters of a constructor be explicitly specified?

    - by sth
    A constructor of a class can be a template function. At the point where such a constructor is called, the compiler usually looks at the arguments given to the constructor and determines the used template parameters from them. Is there also some syntax to specify the template parameters explicitly? A contrived example: struct A { template<typename T> A() {} }; Is there a way to instantiate this class? What is the syntax to explicitly specify the constructor's template parameters? My use case would be a problem were the compiler doesn't seem to find the correct templated constructor. Explicitly specifying the template parameters would probably generate more useful error messages or even resolve the problem.

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  • time(NULL) returning different time

    - by cornerback84
    I am trying to get current time in C using time_t current_time = time(NULL). As I understand, it would return me the current time of system. I am later trying to convert it into GMT time using struct tm* gmt = gmtime(&current_time). I print both times using ctime() and asctime() functions. The current time on my system is GMT + 1. But gmtime() returns me the same time as current_time is. I could not understand why gmtime() is returning me same time. Any help will be appreciated.

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  • C++ Arrays of Structure access

    - by learningtolive
    Hi, I'm studying C++ from Schildt's book and don't quite understand what does he mean under third structure; Can somebody explain this - To access a specific structure within an array of structures, you must index the structure name. For example, to display the on_hand member of the third structure, you would write cout cout << invtry[2].on_hand; Some code: struct type{ char item[40]; double cost; double retail; int on_hand; int lead_time; }invtry[SIZE];

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  • C undefined reference to `some_foo'

    - by sterh
    Hello, I have 3 files in my gtk+ app: main.c: #include <gtk/gtk.h> #include <glib/gi18n.h> #include "mainwindow.h" int main(int argc, char** argv) { MainWin* win; GError* err = NULL; int a = 0; a = some_foo(); gtk_main(); return 0; } mainwindo.h #include <gtk/gtk.h> typedef struct _MainWin { GtkWindow parent; } MainWin; GtkWidget* main_win_new(); int some_foo(); MainWindow.c #include "mainwindow.h" int some_foo() { return 1; } When i try to call some_foo in main function, and try to compile i see error: undefined reference to `some_foo'. What's wrong? Thank you.

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  • is there a flag "M_FAST" in FreeBSD kernel for Malloc Call ?

    - by KaluSingh Gabbar
    if you know there is one, can you let me know what its for ? if not please say so : ) thanks. Signature : void * malloc(unsigned long size, struct malloc_type type, int flags); for example. other flags are... M_ZERO Causes the allocated memory to be set to all zeros. M_WAITOK Indicates that it is OK to wait for resources. If the request cannot be immediately fulfilled, the current process is put to sleep to wait for resources to be released by other processes. The malloc(), realloc(), and reallocf() functions cannot return NULL if M_WAITOK is specified.** This is the root of my confusion EDIT: The clarification for M_FAST is made in my answer below.

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  • Structure within union and bit field

    - by java
    #include <stdio.h> union u { struct st { int i : 4; int j : 4; int k : 4; int l; } st; int i; } u; int main() { u.i = 100; printf("%d, %d, %d", u.i, u.st.i, u.st.l); } I'm trying to figure out the output of program. The first outputs u.i = 100 but I can't understand the output for u.st.i and u.st.l. Please also explain bit fields.

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  • Is it possible to supply template parameters when calling operator()?

    - by Paul
    I'd like to use a template operator() but am not sure if it's possible. Here is a simple test case that won't compile. Is there something wrong with my syntax, or is this simply not possible? struct A { template<typename T> void f() { } template<typename T> void operator()() { } }; int main() { A a; a.f<int>(); // This compiles. a.operator()<int>(); // This compiles. a<int>(); // This won't compile. return 0; }

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  • Another problem with decltype

    - by There is nothing we can do
    template<class IntT, IntT low = IntT(), IntT high = IntT()> struct X { static_assert(std::is_same<decltype(low),decltype(high)>::value,"Different types not allowed");//this should give error if types are different decltype(low) a; decltype(high) b; X():a(decltype(a)()),b(decltype(b)())//WHY THIS DOES NOT COMPILE? { cout << typeid(a).name() << '\n'; cout << typeid(b).name() << '\n'; } }; int _tmain(int argc, _TCHAR* argv[]) { X<char,1,'a'> x;//this according to static_assert shouldn't compile but it does return 0; } Using VS2010. Please see 3 comments in code above.

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  • Problem with CFNetRegister

    - by xtrahotsauce
    I'm trying to work with CFNetServices by trying to start up and publish a service asynchronously. I'm trying to use the example code from here: http://developer.apple.com/mac/library/documentation/Networking/Conceptual/NSNetServiceProgGuide/Articles/CFNetServices.html#//apple_ref/doc/uid/30001276-SW3, but CFNetRegisterWithOptions always fails. (CFNetRegister is deprecated now). When I print out the error struct, it looks like this: (gdb) p error $1 = { domain = 10, error = -72004 } Which doesn't seem correct to me. Does anyone know what might be wrong? Thanks!

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  • What's the simplest way of defining lexicographic comparison for elements of a class?

    - by the_mandrill
    If I have a class that I want to be able to sort (ie support a less-than concept), and it has several data items such that I need to do lexicographic ordering then I need something like this: struct MyData { string surname; string forename; bool operator<(const MyData& other) const { return surname < other.surname || (surname==other.surname && forename < other.forename); } }; This becomes pretty unmanageable for anything with more than 2 data members. Are there any simpler ways of achieving it? The data members may be any Comparable class.

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  • How to remove an item from a structure array in C++?

    - by Antik
    I have the following array structure (linked list): struct str_pair { char ip [50] ; char uri [50] ; str_pair *next ; } ; str_pair *item; I know to create a new item, I need to use item = new str_pair; However, I need to be able to loop through the array and delete a particular item. I have the looping part sorted. But how do I delete an item from an array of structures?

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  • How to know if the argument that is passed to the function is a class, union or enum in c++?

    - by Narek
    I want to define an operator<< for all enums, to cout the value and print that it is an enum like this: code: enum AnyEnum{A,B,C}; AnyEnum enm = A; cout << enm <<endl; output: This is an enum which has a value equal to 0 I know a way of doing this with Boost library by using is_enum struct. But I don’t understand how it works. So that's why, in general, I am interested how to identify if the veriable is a class type, union type or an enum (in compile time).

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