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  • Can I mix compile time string comparison with MPL templates?

    - by Negative Zero
    I got this compile time string comparison from another thread using constexpr and C++11 (http://stackoverflow.com/questions/5721813/compile-time-assert-for-string-equality). It works with constant strings like "OK" constexpr bool isequal(char const *one, char const *two) { return (*one && *two) ? (*one == *two && isequal(one + 1, two + 1)) : (!*one && !*two); } I am trying to use it in the following context: static_assert(isequal(boost::mpl::c_str<boost::mpl::string<'ak'>>::value, "ak"), "should not fail"); But it gives me an compilation error of static_assert expression is not an constant integral expression. Can I do this?

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  • Can this rectangle to rectangle intersection code still work?

    - by Jeremy Rudd
    I was looking for a fast performing code to test if 2 rectangles are intersecting. A search on the internet came up with this one-liner (WOOT!), but I don't understand how to write it in Javascript, it seems to be written in an ancient form of C++. Can this thing still work? Can you make it work? struct { LONG left; LONG top; LONG right; LONG bottom; } RECT; bool IntersectRect(const RECT * r1, const RECT * r2) { return ! ( r2->left > r1->right || r2->right left || r2->top > r1->bottom || r2->bottom top ); }

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  • Template type deduction with a non-copyable class

    - by Evan Teran
    Suppose I have an autolocker class which looks something like this: template <T> class autolocker { public: autolocker(T *l) : lock(l) { lock->lock(); } ~autolocker() { lock->unlock(); } private: autolocker(const autolocker&); autolocker& operator=(const autolocker&); private: T *lock; } Obviously the goal is to be able to use this autolocker with anything that has a lock/unlock method without resorting to virtual functions. Currently, it's simple enough to use like this: autolocker<some_lock_t> lock(&my_lock); // my_lock is of type "some_lock_t" but it is illegal to do: autolocker lock(&my_lock); // this would be ideal Is there anyway to get template type deduction to play nice with this (keep in my autolocker is non-copyable). Or is it just easiest to just specify the type?

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  • How do I define an implicit typecast from my class to a scalar?

    - by Delan Azabani
    I have the following code, which uses a Unicode string class from a library that I'm writing: #include <cstdio> #include "ucpp" main() { ustring a = "test"; ustring b = "ing"; ustring c = "- -"; ustring d; d = "cafe\xcc\x81"; printf("%s\n", (a + b + c[1] + d).encode()); } The encode method of the ustring class instances converts the internal Unicode into a UTF-8 char *. However, because I don't have access to the char class definition, I am unsure on how I can define an implicit typecast (so that I don't have to manually call encode when using with printf, etc).

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  • fread() behaves weird

    - by Cres
    hi, I have a problem in a C program of mine where after I use fread(), the file pointer goes to the end of the file sometimes. I'll try to explain better - the code looks something like: dummy = ftell(fp); fread(&buf, sizeof(unsigned char), 8, fp); dummy = ftell(fp); where fp is a file pointer to an opened file (opened it with "w+", I'm using it as a binary file and I know i'm supposed to have a "b" in there too, but I heard its not really important to add it..), dummy is just an unsigned long variable, and buf is unsigned char[8] now, when debugging, at the ftell before the fread, dummy is 262062 at the ftell after the fread, dummy is 262640 even though I only 'moved' 8 bytes.. does anyone have any idea what can be the cause of this..? thanks for your help :)

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  • Valid signed Hex to long function

    - by Ben
    I am trying to convert a 24bit Hexadecimal string (6 characters) signed in two's complement to a long int in C. This is the function I have come up with: long int hex2li (char string[]) { char *pEnd; long int result = strtol (string, &pEnd, 16); if (strcmp (pEnd, "") == 0) { if (toupper (string[0]) == 'F') { return result - 16777216; } else { return result; } } return LONG_MIN; } Is it valid? Is there a better way of doing this?

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  • C Preprocessor: #define in C... advice

    - by vikramtheone
    Hi Guys, I'm making a big C project and I have never come across a situation like this before so, I need your advice. What is your opinion? Is it okay to have the constants defined within conditional preprocessors like I have done below or you advise me to do this some other way? Any drawbacks if I do it this way? Regards Vikram #define NUM_OCTAVES_4 //#define NUM_OCTAVES_5 #ifdef NUM_OCTAVES_4 #define OCTAVES 4 const unsigned char borders [4] = {11, 26, 50, 98}; #elif NUM_OCTAVES_5 #define OCTAVES 5 const unsigned char borders [5] = {11, 26, 50, 98, 194}; #endif

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  • C++ Undeclared Identifier (but it is declared?)

    - by Joshua
    I'm pretty sure I've included the qanda class, but when I try to declare a vector that contains it or a class of that type I get an error saying that qanda is undefined. Any idea what the problem might be? bot_manager_item.h #pragma once #include "../bot_packet/bot_packet.h" #include <vector> class bot_manager_item; #include "qanda.h" #include "bot_manager.h" class bot_manager_item { public: bot_manager_item(bot_manager* mngr, const char* name, const char* work_dir); ~bot_manager_item(); bool startup(); void cleanup(); void on_push_event(bot_exchange_format f); bool disable; private: void apply_changes(); bot_manager *_mngr; std::string _name; std::string _work_dir; std::string _message; std::string _message_copy; std::vector<qanda> games; qanda test; char _config_full_path[2600]; }; qanda.h #ifndef Q_AND_A #define Q_AND_A #include "users.h" #include "..\bot_packet\bot_packet.h" #include "bot_manager.h" #include <string> #include <algorithm> #include <map> #include <vector> #include <fstream> class qanda { public: qanda(bot_manager * manager, std::string name, std::string directory); ~qanda(){}; void room_message(std::string username, std::string user_message); void timer_tick(); private: // data members std::string question; std::string answer; std::string directory; std::string command_prefix; std::string name; Users users; std::map <std::string, std::string> questions_and_answers; int time_per_question; // seconds int time_between_questions; // seconds int timer; // milliseconds bool is_delayed; bool is_playing; bot_manager * manager; // functions void new_question(); void send_message(std::string msg); void announce_question(); void load_questions(); }; #endif

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  • How to define a static operator<<?

    - by Pietro M
    Is it possible to define a static insertion operator which operates on the static members of a class only? Something like: class MyClass { public: static std::string msg; static MyClass& operator<< (const std::string& token) { msg.append(token); return *this; // error, static } }; alternatively: static MyClass& operator<< (MyClass&, const std::string &token) { MyClass::msg.append(token); return ?; } This is how I would like to use it: MyClass << "message1" << "message2"; Thank you!

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  • use callback function to report stack backtrace

    - by user353394
    Assume I have the following: typedef struct { char *name; char binding; int address; } Fn_Symbol //definition of function symbol static Fn_Symbol *fnSymbols; //array of function symbols in a file statc int total; //number of symbol functions in the array and file static void PrintBacktrace(int sigum, siginfo_t * siginfo, void *context) { printf("\nSignal received %d (%s)\n", signum, strsignal(signum)); const int eip_index = 14; void *eip = (void *)((struct ucontext *)context)->uc_mcontext.gregs[eip_index]; printf("Error at [%p] %s (+0x%x), eip, fnName, offset from start); //????? exit(0); } I have this so far, but what is the best way using the fnSymbols static global pointer to identify the function where the error occured and then back trace through the stack to identify each calling function by address, name, and offset?

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  • CImg compile problems in Codegear 2009

    - by Seth
    I wish to use the CImg library for image processing in my current project. I am using Codegear C++ Builder 2009. I include CImg.h in the source file and put in the following code: int rows =5; int cols = 5; CImg<double> img(rows,cols); I get the following error: [BCC32 Error] CImg.h(39159): E2285 Could not find a match for 'CImg<unsigned char>::move_to<t>(const CImg<unsigned char>)' Does anyone know if there is a #define I should be using when building in Codegear C++ Builder 2009. Or is it simply not compatible?

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  • Boost multiindex complex struct

    - by StrifeLow
    In boost multiindex example complex_structs, it use one key in the car_manufacturer struct for car_table. If car_manufacturer have been modify to have 2 ID struct car_manufacturer { std::string name; int cm_code; car_manufacturer(const std::string& name_, const int& cm_code_):name(name_), cm_code(cm_code_){} }; What will be the key_from_key struct looks like? Have try to add another KeyExtractor or use composite index inside key_from_key, but still cannot compile. Please help on this. Thanks.

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  • [c++] upload image to imageshack

    - by cinek1lol
    Hi! I would like to send pictures via a program written in C + +. - OK WinExec("C:\\curl\\curl.exe -H Expect: -F \"fileupload=@C:\\curl\\ok.jpg\" -F \"xml=yes\" -# \"http://www.imageshack.us/index.php\" -o data.txt -A \"Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1\" -e \"http://www.imageshack.us\"", NULL); It works, but I would like to send the pictures from pre-loaded carrier to a variable char (you know what I mean? First off, I load the pictures into a variable and then send the variable), cause now I have to specify the path of the picture on a disk. I wanted to write this program in c++ by using the curl library, not through exe. extension. I have also found such a program (which has been modified by me a bit) #include <stdio.h> #include <string.h> #include <iostream> #include <curl/curl.h> #include <curl/types.h> #include <curl/easy.h> int main(int argc, char *argv[]) { CURL *curl; CURLcode res; struct curl_httppost *formpost=NULL; struct curl_httppost *lastptr=NULL; struct curl_slist *headerlist=NULL; static const char buf[] = "Expect:"; curl_global_init(CURL_GLOBAL_ALL); /* Fill in the file upload field */ curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "send", CURLFORM_FILE, "nowy.jpg", CURLFORM_END); curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "nowy.jpg", CURLFORM_COPYCONTENTS, "nowy.jpg", CURLFORM_END); curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "submit", CURLFORM_COPYCONTENTS, "send", CURLFORM_END); curl = curl_easy_init(); headerlist = curl_slist_append(headerlist, buf); if(curl) { curl_easy_setopt(curl, CURLOPT_URL, "http://www.imageshack.us/index.php"); if ( (argc == 2) && (!strcmp(argv[1], "xml=yes")) ) curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerlist); curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost); res = curl_easy_perform(curl); curl_easy_cleanup(curl); curl_formfree(formpost); curl_slist_free_all (headerlist); } system("pause"); return 0; }

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  • Strange error: cannot convert from 'int' to 'ios_base::openmode'

    - by Dylan Klomparens
    I am using g++ to compile some code. I wrote the following snippet: bool WriteAccess = true; string Name = "my_file.txt"; ofstream File; ios_base::open_mode Mode = std::ios_base::in | std::ios_base::binary; if(WriteAccess) Mode |= std::ios_base::out | std::ios_base::trunc; File.open(Name.data(), Mode); And I receive these errors... any idea why? Error 1: invalid conversion from ‘int’ to ‘std::_Ios_Openmode’ Error 2: initializing argument 2 of ‘std::basic_filebuf<_CharT, _Traits* std::basic_filebuf<_CharT, _Traits::open(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits]’ As far as I could tell from a Google search, g++ is actually breaking the C++ standard here. Which I find quite astonishing, since they generally conform very strictly to the standard. Is this the case? Or am I doing something wrong. My reference for the standard: http://www.cplusplus.com/reference/iostream/ofstream/open/

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  • boost.asio error on read from socket.

    - by niXman
    The following code of the client: typedef boost::array<char, 10> header_packet; header_packet header; boost::system::error_code error; ... /** send header */ boost::asio::write( _socket, boost::asio::buffer(header, header.size()), boost::asio::transfer_all(), error ); /** send body */ boost::asio::write( _socket, boost::asio::buffer(buffer, buffer.length()), boost::asio::transfer_all(), error ); of the server: struct header { boost::uint32_t header_length; boost::uint32_t id; boost::uint32_t body_length; }; static header unpack_header(const header_packet& data) { header hdr; sscanf(data.data(), "%02d%04d%04d", &hdr.header_length, &hdr.id, &hdr.body_length); return hdr; } void connection::start() { boost::asio::async_read( _socket, boost::asio::buffer(_header, _header.size()), boost::bind( &connection::read_header_handler, shared_from_this(), boost::asio::placeholders::error ) ); } /***************************************************************************/ void connection::read_header_handler(const boost::system::error_code& e) { if ( !e ) { std::cout << "readed header: " << _header.c_array() << std::endl; std::cout << constants::unpack_header(_header); boost::asio::async_read( _socket, boost::asio::buffer(_body, constants::unpack_header(_header).body_length), boost::bind( &connection::read_body_handler, shared_from_this(), boost::asio::placeholders::error ) ); } else { /** report error */ std::cout << "read header finished with error: " << e.message() << std::endl; } } /***************************************************************************/ void connection::read_body_handler(const boost::system::error_code& e) { if ( !e ) { std::cout << "readed body: " << _body.c_array() << std::endl; start(); } else { /** report error */ std::cout << "read body finished with error: " << e.message() << std::endl; } } On the server side the method read_header_handler() is called, but the method read_body_handler() is never called. Though the client has written down the data in a socket. The header is readed and decoded successfully. What's the error?

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  • passing pipe to threads

    - by alaamh
    I see it's easy to open pipe between two process using fork, but how we can passing open pipe to threads. Assume we need to pass out of PROGRAM A to PROGRAM B "may by more than one thread", PROGRAM B send his output to PROGRAM C #include <stdio.h> #include <stdlib.h> #include <pthread.h> struct targ_s { int fd_reader; }; void *thread1(void *arg) { struct targ_s *targ = (struct targ_s*) arg; int status, fd[2]; pid_t pid; pipe(fd); pid = fork(); if (pid == 0) { dup2(STDIN_FILENO, targ->fd_reader); close(fd[0]); dup2(fd[1], STDOUT_FILENO); close(fd[1]); execvp ("PROGRAM B", NULL); exit(1); } else { close(fd[1]); dup2(fd[0], STDIN_FILENO); close(fd[0]); execl("PROGRAM C", NULL); wait(&status); return NULL; } } int main(void) { FILE *fpipe; char *command = "PROGRAM A"; char buffer[1024]; if (!(fpipe = (FILE*) popen(command, "r"))) { perror("Problems with pipe"); exit(1); } char* outfile = "out.dat"; FILE* f = fopen (outfile, "wb"); int fd = fileno( f ); struct targ_s targ; targ.fd_reader = fd; pthread_t thid; if (pthread_create(&thid, NULL, thread1, &targ) != 0) { perror("pthread_create() error"); exit(1); } int len; while (read(fpipe, buffer, sizeof (buffer)) != 0) { len = strlen(buffer); write(fd, buffer, len); } pclose(fpipe); return (0); }

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  • Why does SQLite not bring back any results from my database

    - by tigermain
    This is my first SQLite based iPhone app and I am trying to get it to read a menu hierarchy from my database. The database appears to be registered fine as the compiled statement doesnt error (tried putting in valid table name to test) but for some reason sqlite3_step(compiledStmt) doesnt ever equal SQLITE_ROW as if to suggest there is no data in there; which there is. sqlite3 *database; menu = [[NSMutableArray alloc] init]; if (sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) { const char *sqlStmt = "SELECT * FROM Menu"; sqlite3_stmt *compiledStmt; if (sqlite3_prepare_v2(database, sqlStmt, -1, &compiledStmt, NULL) == SQLITE_OK) { while (sqlite3_step(compiledStmt) == SQLITE_ROW) { NSString *aTitle = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStmt, 1)]; MenuItem *menuItem = [[MenuItem alloc] init]; menuItem.title = aTitle; [menu addObject:menuItem]; [menuItem release]; } } else { NSLog(@"There is an error with the SQL Statement"); } sqlite3_finalize(compiledStmt); } sqlite3_close(database);

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  • Jakarta Regexp 1.5 Backreferences?

    - by Matt Smith
    Why does this match: String str = "099.9 102.2" + (char) 0x0D; RE re = new RE("^([0-9]{3}.[0-9]) ([0-9]{3}.[0-9])\r$"); System.out.println(re.match(str)); But this does not: String str = "099.9 102.2" + (char) 0x0D; RE re = new RE("^([0-9]{3}.[0-9]) \1\r$"); System.out.println(re.match(str)); The back references don't seem to be working... What am I missing?

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  • How to access a structure member in a function that get it as void* type?

    - by Ahmad
    I want to have a function that accepts different type of structures as argument. So, since I don't have a specific type, I have to use void*. Now question is: when I pass a structure to this function, how can I access a known member of this structure inside the function? Specifically, I know that all structures have str1 as a member and I want, for example, print it. Here is a sample code: struct { char* str1; float tt1; } var1 = {"This is me", 12}; struct { char* str1; int tt2; } var2 = {"This is you", 18}; void printStruct(void* str) { printf("\n the structure string is %s", ??); //can I put something in ?? to print the string? } main(....) { printStruct(&var1); printStruct(&var2); }

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  • C++ interface inheritance problem

    - by james t
    Hey, i'm trying to create a c++ stomp client, my client constructor is : Client(std::string &server, short port, std::string &login, std::string &pass, Listener &listener); it gets a listener object which when Listener is the following interface : class Listener { virtual void message(StmpMessage message) =0; }; now i attempt to instantiate a client in a test class : class test : public virtual Listener { public: void message(StmpMessage message) { message.prettyPrint(); } int main(int argc, char* argv[]) { Client client("127.0.0.1", 61613, *this); return 0; } }; i'm sending this to the client because this is a listener object, i get the following error : /Users/mzruya/Documents/STOMPCPP/main.cpp:18: error: no matching function for call to 'Client::Client(const char [10], int, test&)' /Users/mzruya/Documents/STOMPCPP/Client.h:43: note: candidates are: Client::Client(std::string&, short int, std::string&, std::string&, Listener&) /Users/mzruya/Documents/STOMPCPP/Client.h:37: note: Client::Client(const Client&)

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  • Implementing operator< in C++

    - by Vulcan Eager
    I have a class with a few numeric fields such as: class Class1 { int a; int b; int c; public: // constructor and so on... bool operator<(const Class1& other) const; }; I need to use objects of this class as a key in an std::map. I therefore implement operator<. What is the simplest implementation of operator< to use here?

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  • How can i assign a two dimensional array into other temporary two dimensional array.....?? in C Programming..

    - by AGeek
    Hi I am trying to store the contents of two dimensional array into a temporary array.... How is it possible... I don't want looping over here, as it would add an extra overhead.. Any pointer notation would be good. struct bucket { int nStrings; char strings[MAXSTRINGS][MAXWORDLENGTH]; }; void func() { char **tArray; int tLenArray = 0; for(i=0; i<TOTBUCKETS-1; i++) { if(buck[i].nStrings != 0) { tArray = buck[i].strings; tLenArray = buck[i].nStrings; } } } The error here i am getting is:- [others@centos htdocs]$ gcc lexorder.c lexorder.c: In function âlexSortingâ: lexorder.c:40: warning: assignment from incompatible pointer type Please let me know if this needs some more explanaition...

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  • How to take input for a character pointer without using fget?

    - by ashish yadav
    consider the code #include<stdio.h> int main() { char* a; scanf("%s",a);//&a and &a[0] give same results-crashes printf("%s",); return 0; } why does this code results in crashing?whereas this code using character array works fine? #include<stdio.h> int main() { char a[100]; scanf("%s",&a[0]);//works fine printf("%s",a); return 0; } the difference being character array and pointer?but i knew that pointer just points to the first element that is &a[0] should work fine but upper code crashes for all three that is a,&a and &a[0]? the main thing i would to gather is how can i take input of a character pointer if i insist on using scanf only? i apologize if i am not clear. thanks in advance:)

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  • JNI cached jclass global reference variables being garbage collected?

    - by bubbadoughball
    I'm working in the JNI Invocation API, calling into Java from C. I have some upfront initialization to cache 30+ Java classes into global references. The results of FindClass are passed into NewGlobalRef to acquire a global reference to the class. I'm caching these class variables to reuse them later. I have 30+ global references to classes (and 30+ global methodIDs for the class constructors). In the following sample, I've removed exception handling as well as JNI invocation for the purpose of shortening the code snippet. My working code has exception checks after every JNI call and I'm running with -Xcheck:jni. Here's the snippet: jclass aClass; jclass bClass; jmethodID aCtor; jmethodID bCtor; void getGlobalRef(const char* clazz, jclass* globalClass) { jclass local = (*jenv)->FindClass(jenv,clazz); if (local) { *globalClass = (jclass) (*jenv)->NewGlobalRef(jenv,local); (*jenv)->DeleteLocalRef(jenv,local); } } methodID getMethodID(jclass clazz, const char* method, const char* sig) { return (*jenv)->GetMethodID(jenv,clazz,method,sig); } void initializeJNI() { getGlobalRef("MyProj/Testclass1", &aclass); getGlobalRef("MyProj/Testclass2", &bclass); . . aCtor = getMethodID(aclass,"<init>","()V"); bCtor = getMethodID(bclass,"<init>","(I)V"); } The initializeJNI() function sets the global references for jclasses and method IDs for constructors as well as some jfieldID's and some initialization of C data structures. After initialization, when I call into a JNI function using some of the cached jclasses and ctor jmethodIDs, I get a bad global or local reference calling reported from the -Xcheck:jni. In gdb, I break at the last line of initializeJNI(), and print all jclasses and jmethodIDs and the ones causing problems look to have been turned into garbage or garbage-collected (i.e. 0x00 or 0x06). Is it possible for global references to be gc'ed? Any suggestions?

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  • Simple question about C++ constant syntax

    - by WilliamLou
    Here is some code copied from Thinking in C++ Vol1 Chapter 10. #include <iostream> using namespace std; int x = 100; class WithStatic { static int x; static int y; public: void print() const { cout << "WithStatic::x = " << x << endl; cout << "WithStatic::y = " << y << endl; } }; what's the meaning of const for the function print()? Thanks!

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