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  • Is 'bool' a basic datatype in C++ ?

    - by Naveen
    I got this doubt while writing some code. Is 'bool' a basic datatype defined in the C++ standard or is it some sort of extension provided by the compiler ? I got this doubt because Win32 has 'BOOL' which is nothing but a typedef of long. Also what happens if I do something like this: int i = true; Is it "always" guaranteed that variable i will have value 1 or is it again depends on the compiler I am using ? Further for some Win32 APIs which accept BOOL as the parameter what happens if I pass bool variable?

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  • Static initialization of a struct with class members

    - by JS Bangs
    I have a struct that's defined with a large number of vanilla char* pointers, but also an object member. When I try to statically initialize such a struct, I get a compiler error. typedef struct { const char* pszA; // ... snip ... const char* pszZ; SomeObject obj; } example_struct; // I only want to assign the first few members, the rest should be default example_struct ex = { "a", "b" }; SomeObject has a public default constructor with no arguments, so I didn't think this would be a problem. But when I try to compile this (using VS), I get the following error: error C2248: 'SomeObject::SomeObject' : cannot access private member declared in class 'SomeObject' Any idea why?

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  • Assigning two strings together getting Access Read Violation

    - by Jay Bell
    I am trying to pass a string to a class mutator and set the private member to that string here is the code that is sending the string void parseTradePairs(Exchange::Currency *curr, std::string *response, int begin, int exit) { int start; int end; string temp; string dataResponse; CURL *tempCurl; initializeCurl(tempCurl); int location = response->find("marketid", begin); if(location <= exit) { start = location + 11; begin = response->find("label", start); end = begin - start - 3; findStrings(start, end, temp, response); getMarketInfo(tempCurl, temp, dataResponse); curr->_coin->setExch(temp); // here is the line of code that is sending the string dataResponse >> *(curr->_coin); curr->_next = new Exchange::Currency(curr, curr->_position + 1); parseTradePairs(curr->_next, response, begin, exit); } } and here is the mutator within the coin class that is receiving the string and assigning it to _exch void Coin::setExch(string exch) { _exch = exch; } I have stepped through it and made sure that exch has the string in it. "105" but soon as it hits _exch = exch; I get the reading violation. I tried passing as pointer as well. I do not believe it should go out of scope. and the string variable in the class is initialized to zero in the default constructor but again that should matter unless I am trying to read from it instead of writing to it. /* defualt constructor */ Coin::Coin() { _id = ""; _label = ""; _code= ""; _name = ""; _marketCoin = ""; _volume = 0; _last = 0; _exch = ""; } Exchange::Exchange(std::string str) { _exch = str; _currencies = new Currency; std::string pair; std::string response; CURL *curl; initializeCurl(curl); getTradePairs(curl, response); int exit = response.find_last_of("marketid"); parseTradePairs(_currencies, &response, 0, exit); } int main(void) { CURL *curl; string str; string id; Coin coin1; initializeCurl(curl); Exchange ex("cryptsy"); curl_easy_cleanup(curl); system("pause"); return 0; } class Exchange { public: typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() : _next(NULL), _prev(NULL), _position(0) {} Coin *_coin; Currency *_next; Currency *_prev; int _position; }; /* constructor and destructor */ Exchange(); Exchange(std::string str); ~Exchange(); /* Assignment operator */ Exchange& operator =(const Exchange& copyExchange); /* Parse Cryptsy Pairs */ friend void parseTradePairs(Currency *curr, std::string *response, int begin, int exit); private: std::string _exch; Currency *_currencies; }; here is what i changed it to to fix it. typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() { _next = NULL; _prev = NULL; _position = 0; _coin = new Coin(); } Coin *_coin; Currency *_next; Currency *_prev; int _position; };

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  • How do I iterate over a tuple

    - by Caligo
    How can I iterate over a tuple starting from, say, index 1 to 2? The following doesn't work. using boost::fusion::cons; typedef cons<A, cons<B, cons<C, cons<D> > > > MyTuple; MyTuple tuple_; template <class T> struct DoSomething{ DoSomething(T& t) : t_(&t){ } template <class U> void operator()(U u){ boost::fusion::at<mpl::int_<u> >(*t_); } T* t_; }; boost::mpl::for_each< boost::mpl::range_c<int, 1, 3> >( DoSomething<MyTuple>(tuple_) );

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  • How can I declare a pointer structure using {}?

    - by Y_Y
    This probably is one of the easiest question ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head and still leave it out in the global scope? For example: //not legal!!! struct node *head = {10,&head,&head};

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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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  • 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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  • C/C++ enums: Detect when multiple items map to same value

    - by Dan
    Is there a compile-time way to detect / prevent duplicate values within a C/C++ enumeration? The catch is that there are multiple items which are initialized to explicit values. Background: I've inherited some C code such as the following: #define BASE1_VAL (5) #define BASE2_VAL (7) typedef enum { MsgFoo1A = BASE1_VAL, // 5 MsgFoo1B, // 6 MsgFoo1C, // 7 MsgFoo1D, // 8 MsgFoo1E, // 9 MsgFoo2A = BASE2_VAL, // Uh oh! 7 again... MsgFoo2B // Uh oh! 8 again... } FOO; The problem is that as the code grows & as developers add more messages to the MsgFoo1x group, eventually it overruns BASE2_VAL. This code will eventually be migrated to C++, so if there is a C++-only solution (template magic?), that's OK -- but a solution that works with C and C++ is better.

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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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  • Tools for understanding large codebase

    - by 0tar0gz
    Hi! My whole life I have been programming in simple plain text editor. Lately, I was contemplating about joining an open source project which is fairly large and written in C. I downloaded the sources, started to look around, read this, forget that... Then I thought to myself: this can't be true. This is 21st century there must be some tool which would help me to understand the code, perhaps some kind of IDE or "code navigator". What flows from here to where, this typedef struct is just interface to that private type, this function is just #define from above, function called in this file is defined in that file, ... you get the idea. Dear Stack Overflow, is this 21st century? Is there something like this?

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  • Policies Array Class-Design wrapper

    - by PT
    Hi, i want to write an wrapper for different Array Classes with different Policies. For example: typedef ArrayType<useValArray,StdAllocator> Array; // one global assignment I want to use the class like a blitz++ Array for example: Array<double,2> x(2,2); //maps the Array to an Valarray or to a Blitz++ Array Array<double,2> x2(5,6); is this Posible? Which technics i need to realise that?

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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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  • writing structs and classes to disk

    - by Phenom
    The following function writes a struct to a file. int btwrite(short rrn, BTPAGE *page_ptr) { long addr; addr = (long) rrn * (long) PAGESIZE + HEADERSIZE; lseek(btfd, addr, 0); return (write(btfd, page_ptr, PAGESIZE)); } The following is the struct. typedef struct { short keycount; /* number of keys in page */ int key[MAXKEYS]; /* the actual keys */ int value[MAXKEYS]; /* the actual values */ short child[MAXKEYS+1]; /* ptrs to rrns of descendants */ } BTPAGE; What would happen if I changed the struct to a class, would it still work the same? If I added class functions, would the size it takes up on disk increase?

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  • Does this make any sense (Apple-documentation)?

    - by Paperflyer
    Here is a snippet of the official Apple Documentation of AudioBufferList (Core Audio Data Types Reference) AudioBufferList Holds a variable length array of AudioBuffer structures. struct AudioBufferList { UInt32 mNumberBuffers; AudioBuffer mBuffers[1]; }; typedef struct AudioBufferList AudioBufferList; Fields mNumberBuffers The number of AudioBuffer structures in the mBuffers array. mBuffers A variable length array of AudioBuffer structures. If mBuffers is defined as AudioBuffer[1] it is not of variable length and thus mNumberBuffers is implicitly defined as 1. Do I miss something here or is this just nonsense?

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  • assignment from incompatible pointer type

    - by Hristo
    I have set up the following struct: typedef struct _thread_node_t { pthread_t thread; struct thread_node_t *next; } thread_node_t; ... and then I have defined: // create thread to for incoming connection thread_node_t *thread_node = (thread_node_t*) malloc(sizeof(thread_node_t)); pthread_create(&(thread_node->thread), NULL, client_thread, &csFD); thread_node->next = thread_arr; // assignment from incompatible pointer type thread_arr = thread_node; where thread_arr is thread_node_t *thread_arr = NULL; I don't understand why the compiler is complaining. Maybe I'm misunderstanding something.

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  • Why do you sometimes need to write <typename T> instead of just <T> ?

    - by StackedCrooked
    I was reading the Wikipedia article on SFINAE and encountered following code sample: struct Test { typedef int Type; }; template < typename T > void f( typename T::Type ) {} // definition #1 template < typename T > void f( T ) {} // definition #2 void foo() { f< Test > ( 10 ); //call #1 f< int > ( 10 ); //call #2 without error thanks to SFINAE } Now I've actually written code like this before, and somehow intuitively I knew that I needed to type "typename T" instead of just "T". However, it would be nice to know the actual logic behind it. Anyone care to explain?

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  • Typechecking macro arguments in C

    - by Rocketmagnet
    Hi all, Is is possible to typecheck arguments to a #define macro? For example: typedef enum { REG16_A, REG16_B, REG16_C }REG16; #define read_16(reg16) read_register_16u(reg16); \ assert(typeof(reg16)==typeof(REG16)); The above code doesn't seem to work. What am I doing wrong? BTW, I am using gcc, and I can guarantee that I will always be using gcc in this project. The code does not need to be portable.

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  • Compilation failing - no #include - boost

    - by jwoolard
    Hi, I'm trying to compile a third-party library, but g++ is complaining about the following line: typedef boost::shared_ptr<MessageConsumer> MessageConsumerPtr; The strange thing is, there is no #include directive in the file - and it is clearly supposed to be this way; there are about 60 files with the same (or very similar) issues. Clearly if there was an #include directive referencing the relevant boost header this would compile cleanly. My question is: how can I get g++ to somehow automagically find the relevant symbol (in all instances of this issue, it is a namespace that can't be found - usually std:: or boost::) by either automatically processing the relevant header (or some other mechanism). Thanks. Edit My current g++ call looks like: g++ -fPIC -O3 -DUSING_PCH -D_REENTRANT -I/usr/include/boost -I./ -c MessageInterpreter.cpp -o MessageInterpreter.o

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  • Adapting Map Iterators Using STL/Boost/Lambdas

    - by John Dibling
    Consider the following non-working code: typedef map<int, unsigned> mymap; mymap m; for( int i = 1; i < 5; ++i ) m[i] = i; // 'remove' all elements from map where .second < 3 remove(m.begin(), m.end(), bind2nd(less<int>(), 3)); I'm trying to remove elements from this map where .second < 3. This obviously isn't written correctly. How do I write this correctly using: Standard STL function objects & techniques Boost.Bind C++0x Lambdas I know I'm not eraseing the elements. Don't worry about that; I'm just simplifying the problem to solve.

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  • Stucture with array of pointers in C

    - by MVTCplusplus
    What's wrong with this? Can I have an array of pointers to SDL_Surfaces in a struct in C? typedef struct { int next_wheel; int pos_X; int pos_Y; int front_wheel_pos_X; int front_wheel_pos_Y; int velocity; int rear_wheel_pos_X; int rear_wheel_pos_Y; SDL_Surface* body; SDL_Surface* rear_wheel[9]; SDL_Surface* front_wheel[9]; } mars_rover; ... mars_rover* init_rover() { mars_rover* rover = (mars_rover*)malloc(sizeof(mars_rover) + sizeof(SDL_Surface) * 19); ... return rover; } int main() { mars_rover* rover = init_rover(); ... }

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  • iOS Development: How can I encapsulate a string in an NSData object?

    - by BeachRunnerJoe
    Hello. I'm building a multiplayer game on the iPhone and I need to send string data to the other players in the game. To do that, I need to encapsulate my NSString* string data in an NSData object somehow. Here's an example of how my code is structured... typedef struct { PACKETTYPE packetType; ??? stringToSend; //<---not sure how to store this } StringPacket; StringPacket msg; msg.packetType = STRING_PACKET; msg.stringToSend = ... // <---not sure what to do here NSData *packet = [NSData dataWithBytes:&msg length:sizeof(StringPacket)]; So my question is, if StringPacket is a struct defined in my header, what type should the stringToSend property be so that I can easily call the dataWithBytes method of NSData to encapsulate the packet data in an NSData object? Thanks for your wisdom!

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  • Redundant naming in C/C++ typedefs/structs

    - by bloomy
    #include <stdio.h> #include <string.h> const int NAMELEN=30; const int MAXCLASSSIZE=10; typedef struct StudentRec { char lastname[NAMELEN]; char firstname[NAMELEN]; long int ID; int finalmark; }Student; I'm new to coding..and I have a question about why there is Student; after the bracket.. is it a format that we have to follow.

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  • How to algorithmically partion a keyspace?

    - by pbhogan
    This is related to consistent hashing and while I conceptually understand what I need to do, I'm having a hard time translating this into code. I'm trying to divide a given keyspace (say, 128 bits) into equal sized partitions. I want the upper bound (highest key) of each partition. Basically, how would I complete this? #define KEYSPACE_BYTE_SIZE 16 #define KEYSPACE_BIT_SIZE (KEYSPACE_BYTE_SIZE * 8) typedef struct _key { char byte[KEYSPACE_BYTE_SIZE]; } key; key * partition_keyspace( int num_partitions ) { key * partitions = malloc( sizeof(key) * num_partitions ); // ... }

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  • Cast A primitive type pointer to A structure pointer - Alignment and Padding?

    - by Seçkin Savasçi
    Just 20 minutes age when I answered a question, I come up with an interesting scenario that I'm not sure of the behavior: Let me have an integer array of size n, pointed by intPtr; int* intPtr; and let me also have a struct like this: typedef struct { int val1; int val2; //and less or more integer declarations goes on like this(not any other type) }intStruct; My question is if I do a cast intStruct* structPtr = (intStruct*) intPtr; Am I sure to get every element correctly if I traverse the elements of the struct? Is there any possibility of miss-alignment(possible because of padding) in any architecture/compiler?

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