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• Are pointers primitive types in C++?

  - by Space_C0wb0y

  I was wondering about the last constructor for std::string mentioned here. It says: template<class InputIterator> string (InputIterator begin, InputIterator end); If InputIterator is an integral type, behaves as the sixth constructor version (the one right above this) by typecasting begin and end to call it: string(static_cast<size_t>(begin),static_cast<char>(end)); In any other case, the parameters are taken as iterators, and the content is initialized with the values of the elements that go from the element referred by iterator begin to the element right before the one referred by iterator end. So what does that mean if InputIterator is a char * ?

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• How might I assume a "default value" when parsing using boost::spirit?

  - by tJener

  Let's say I have a grammar defined to something like: a b c d where c, and d are optional and default to 14 if not given. Can I get it to automatically return the 14 if the value isn't given? The closest I've come is like the following: qi::rule<Iterator, std::vector<int>(), ascii::space_type> some_rule; some_rule %= >> int_ >> int_ >> -int_ >> -int_; // ... some_other_rule = some_rule[&some_callback_for_int_vectors]; which will then get 0 for the optional values that didn't show up (I believe). I then change consecutive 0s at the end into 14. Not only is this horribly wrong, but its also just not elegant. Is there a better way to do this?

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• CryptGenRandom to generate asp.net session id

  - by DoDo

  Hi! does anyone have working example of CryptGenrRandom class to generate session id (need to use in my iis module). HCRYPTPROV hCryptProv; BYTE pbData[16]; if(CryptAcquireContext( &hCryptProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) { if(CryptGenRandom(hCryptProv, 8, pbData)) { std::string s(( const char *) pbData); printf(s.c_str()); } else { MyHandleError("Error during CryptGenRandom."); } } else { MyHandleError("Error during CryptAcquireContext!\n"); } i tried this code but, its not working quite well (i get it from msdn) and this example don't work for me ( http://www.codeproject.com/KB/security/plaintextsessionkey.aspx ) so if anyone know how to generate sessionid using this class plz let me know tnx anyway!

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• Difference between debug and release.

  - by atch

  Why when I'm debugging in debug mode everything in code below works as suppose to but when I switch to release I'm getting strange result? void say_hello(int argc, char* argv[])//In release mode argc has different values from 124353625 to 36369852 <include iostream> { std::cout << "In say_hello()\n"; } int main(int argc, char* argv[]) { say_hello(3,argv);//when instead of literal I enter "argc" everything is ok. return 0; } Thanks for help.

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• C++ enumeration

  - by asli

  Hi,my question is about enumeration,my codes are : #include<iostream> using namespace std; int main() { enum bolumler {programcilik,donanim,muhasebe,motor,buro} bolum; bolum = donanim; cout << bolum << endl; bolum += 2; // bolum=motor cout << bolum; return 0; } The output should be 1 3 but according to these codes the error is: error C2676: binary '+=' : 'enum main::bolumler' does not define this operator or a conversion to a type acceptable to the predefined operator Error executing cl.exe. 111.obj - 1 error(s), 0 warning(s) Can you help me ?The other question is what can I do if I want to see the output like that "muhasebe"?

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• What's wrong with the following code ?

  - by dada

  #include <iostream> #include <string> using namespace std; int main(void) { string a; cin>>a; a.erase(a.end()-1); a.erase(a.begin()+1); string ge = "oae"; a.insert(a.begin()+1, ge); cout<<a<<endl; return 0; } It doesn't compile and i don't know why. Can you tell me what's wrong

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• some verd problems in qt

  - by prabhakaran

  I am very new to qt, So whatever I facing is either errors or problems. Here goes some of them, 1)Just try to install it in VisualStudio, you will got enough for the day. 2)After you installed it as a separate qt(without embedding it inside visual studio).Open a c++ file in qt, = then you won't get any option to compile it. 3)Create a empty qt4 project like below #include<iostream> using namespace std; int main(int a,char * argv[]) { } Then build it, you will get a error like this C:\qt-greenhouse\Trolltech\Code_less_create_more\Trolltech\Code_less_create_more\Troll\4.6\qt\src\winmain/qtmain_win.cpp:131: undefined reference to `qMain(int, char**)' Can anybody clear any of these problems to me.

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• Pass temporary object to function that takes pointer

  - by Happy Mittal

  I tried following code : #include<iostream> #include<string> using namespace std; string f1(string s) { return s="f1 called"; } void f2(string *s) { cout<<*s<<endl; } int main() { string str; f2(&f1(str)); } But this code doesn't compile. What I think is : f1 returns by value so it creates temporary, of which I am taking address and passing to f2. Now Please explain me where I am thinking wrong?

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• Why is this c++ string concatenation missing a space?

  - by danutenshu

  I am working with c++ strings, and am a beginner at programming. I am expecting: 99 Red Balloons But I am receiving: 99 RedBalloons Why is that? #include <string> #include <iostream> using namespace std; int main() { string text = "9"; string term( "9 "); string info = "Toys"; string color; char hue[4] = {'R','e','d','\0'}; color = hue; info = "Balloons"; text += (term + color + info); cout << endl << text << endl; return 0; }

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• Are raw C++ pointers first class objects?

  - by Shailesh Kumar

  According to Wikipedia: An object is first-class when it: can be stored in variables and data structures can be passed as a parameter to a subroutine can be returned as the result of a subroutine can be constructed at runtime has intrinsic identity (independent of any given name) Somebody had once told me that raw pointers are not first class objects while smart pointers like std::auto_ptr are. But to me, a raw pointer (to an object or to a function) in C++ does seem to me to satisfy the conditions stated above to qualify as a first class object. Am I missing something?

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• Returning new base class when the parent class shared pointer is the return type

  - by Ben Dol

  Can you have a parent class shared pointer return type of a function and then return a new child class without it being a shared pointer? I'm not sure how shared pointers work in these situations, do they act like a regular pointer? Here is my example: BaseEventPtr Actions::getEvent(const std::string& nodeName) { if(asLowerCaseString(nodeName) == "action") return new ActionEvent(&m_interface); return nullptr; } ActionEvent is the subclass of BaseEvent in this situation. Cheers!

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• Behavior with primitive data types' value out of range & C99's PRI* macros

  - by Yktula

  Say we have an 8-bit unsigned integer n (UINT8_MAX=255); what is the behavior of the compiler for n=256? Where can I find a table of default behavior when the value of a data type is out of range for different data types? Is there a pattern to how they behave when set out of range? #include <stdio.h> #include <inttypes.h> uint8_t n = UINT8_MAX; int main() { printf("%hhu ",n++); printf("%hhu",n); return 0; } Compiling with gcc -std=c99 -Wall *.c, this prints: 255 0 Also, is it acceptable to use C99's PRI* macros? How are they named?

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• C++ STL map.find() not finding my stuff

  - by Joe

  Hello, I have constructed a map and loaded it with data. If I iterate over all the elements I see they are all valid. However, the find method doesn't find my item. I'm sure it's something stupid I am doing. Here is snippet: // definitions // I am inserting a person class and using the firstname as the key typedef std::map<char*,Person *> mapType; mapType _myMap; mapType::iterator _mapIter; ... Person *pers = new Person(FirstName, LastName, Address, Phone); _myMap.insert(make_pair(pers->firstName, pers); ... ...later.... _mapIter = _myMap.find(firstName); // returns map.end _mapIter = _myMap.find("joe"); // returns map.end and I have no idea why :(

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• Excess elements in scalar initializer

  - by Wade Williams

  I'm pretty noobish when it comes to C++ STL stuff. After a compiler upgrade, I'm getting: error: Semantic Issue: Excess elements in scalar initializer on the call: Certificate *tempcert; cValType( tempPerson->name, tempcert ); with a typedef of: typedef std::map< string, certificate* >::value_type cValType; I'm not certain what this error is telling me or how to fix it. (Ok, I realize it's telling me excess elements, but it looks like it matches the map prototype to me, so I'm confused.) Suggestions?

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• the problem only happens when i try create a release...

  - by ace

  I'm sorry if im not presenting this right, but i trully cannot understand what the problem is. i have a project to hand in, a code of 600 lines defined within a main, .cpp, and header file. if i compile the project with just a debugger and no release, it's fine. when i create it with the release, the following error occurs, for every function!!! 1st error: |36|multiple definition of `countLines(int&, std::vector const&)'| 2nd error: |36|first defined here| if someone will allow me and i can send them the entire code, that would be awesome - i have to have this done within 3 hours.

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• HowTo parse numbers from string with BOOST methods?

  - by mosg

  Problem: Visual C++ 10 project (using MFC and Boost libraries). In one of my methods I'm reading simple test.txt file. Here is what inside of the file (std::string): 12 asdf789, 54,19 1000 nsfewer:22!13 Then I'm reading it and I have to convert all digits to int only with boost methods. For example, I have a list of different characters which I have to parse: ( ’ ' ) ( [ ], ( ), { }, ? ? ) ( : ) ( , ) ( ! ) ( . ) ( - ) ( ? ) ( ‘ ’, “ ”, « » ) ( ; ) ( / ) And after conversation I must have some kind of a massive of int's values, like this one: 12,789,54,19,1000,22,13 Maybe some one already did this job? PS. I'm new for boost. Thanks!

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• problem in reading output of dd command using pipe

  - by Ummar

  I am developing an application, in which I want to redirect the output (progress information) of dd command to my C++ program, but it is not actually getting the output, here is the code FILE * progressInfo = popen("gzip -dc backup/backup.img.gz | pv -ptrbe -i 2 -s 2339876653 | dd of=/dev/sdb","r"); if(!progressInfo) { return -1; } char buf[1024]; while(fgets(buff, sizeof(buff),progressInfo)!=NULL) { std::cout << buff << endl; } but the problem is the progress information is not received in buff, and the output is continuously printed on terminal, and above program halts on while(fgets(buff, sizeof(buff),progressInfo)!=NULL), and as soon as the dd operation is completed, the very next line to loop block is executed. if anyone has any idea why the output is not returned to buff, and its continuously retuned on terminal?

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• c++ function overloading, making fwrite/fread act like PHP versions

  - by Newbie

  I'm used to the PHP fwrite/fread parameter orders, and i want to make them the same in C++ too. I want it to work with char and string types, and also any data type i put in it (only if length is defined). I am total noob on c++, this is what i made so far: size_t fwrite(FILE *fp, const std::string buf, const size_t len = SIZE_MAX){ if(len == SIZE_MAX){ return fwrite(buf.c_str(), 1, buf.length(), fp); }else{ return fwrite(buf.c_str(), 1, len, fp); } } size_t fwrite(FILE *fp, const void *buf, const size_t len = SIZE_MAX){ if(len == SIZE_MAX){ return fwrite((const char *)buf, 1, strlen((const char *)buf), fp); }else{ return fwrite(buf, 1, len, fp); } } Should this work just fine? And how should this be done if i wanted to do it the absolutely best possible way?

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• Doesnt the Visual Studio 2008 compiler autocast to double with sqrt in C++?

  - by Chris_45

  Shouldn't the compiler automatically cast to a double in this case at least according to Walter Savitch: #include <iostream> #include <cmath> using namespace std; int main(){ int k; for(k = 1; k <= 10; k++) cout << "The square root of i is: " << sqrt(k) << endl; return 0; }//error C2668: 'sqrt' : ambiguous call to overloaded function //Visual Studio 2008 on Win Vista

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• how to read integers from file and write each integer into different name integer?

  - by Aivaras

  This is how the program looks and i need to make all integers with different name. Like x,x1,x2 and so on... #include <cstdlib> #include <iostream> #include <fstream> using namespace std; int main() { ifstream iFile("input.txt"); // input.txt has integers, one per line while (true) { int x; iFile >> x; if( iFile.eof() ) break; cerr << x << endl; } system("Pause"); return 0; }

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• read pair of characters separated by \t c++

  - by Kiran

  Friends, I want to read a pair of characters separated by \t. I want to continue reading the input until user enters z for any of the characters. Here are the options I thought: while (cinch1ch2) { // process ch1 & ch2 } std::string str; while (getline(cin, str) ){ //split string } Also, I want to validate the input to make sure that it is correct. Please suggest the best way. If this is a duplicate, please point me to the right one. Thanks.

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• Whats wrong with the following code, its not compiling

  - by Ganesh Kundapur

  #include <iostream> #include <vector> using namespace std; class Base { public: void Display( void ) { cout<<"Base display"<<endl; } int Display( int a ) { cout<<"Base int display"<<endl; return 0; } }; class Derived : public Base { public: void Display( void ) { cout<<"Derived display"<<endl; } }; void main() { Derived obj; obj.Display(); obj.Display( 10 ); } $test1.cpp: In function ‘int main()’: test1.cpp:35: error: no matching function for call to ‘Derived::Display(int)’ test1.cpp:24: note: candidates are: void Derived::Display() On commenting obj.Display(10), it works.

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• What to return as an iterator when there is no container?

  - by DaClown

  I have an inheritance structure of objects with begin() and end() as pure virtual member functions in the base class. From this objects I'm planning to build a composite structure. This inner objects have std::vector member the begin() and end() get their data from. But in a leaf class there is no vector. Now I try to find a return value for begin() and end() in the leaf classes. What would be a good way to do that? The easiest way would be to have a vector member in the leaf classes with no elements in it to fuel begin() and end(), but this just doesn't feel right.

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• Multithreading with STL container

  - by Steven

  I have an unordered map which stores a pointer of objects. I am not sure whether I am doing the correct thing to maintain the thread safety. typedef std::unordered_map<string, classA*>MAP1; MAP1 map1; pthread_mutex_lock(&mutexA) if(map1.find(id) != map1.end()) { pthread_mutex_unlock(&mutexA); //already exist, not adding items } else { classA* obj1 = new classA; map1[id] = obj1; obj1->obtainMutex(); //Should I create a mutex for each object so that I could obtain mutex when I am going to update fields for obj1? pthread_mutex_unlock(&mutexA); //release mutex for unordered_map so that other threads could access other object obj1->field1 = 1; performOperation(obj1); //takes some time obj1->releaseMutex(); //release mutex after updating obj1 }

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• How to interrupt a waiting C++0x thread?

  - by doublep

  I'm considering to use C++0x threads in my application instead of Boost threads. However, I'm not sure how to reimplement what I have with standard C++0x threads since they don't seem to have an interrupt() method. My current setup is: a master thread that manages work; several worker threads that carry out master's commands. Workers call wait() on at least two different condition variables. Master has a "timed out" state: in this case it tells all workers to stop and give whatever result they got by then. With Boost threads master just uses interrupt_all() on a thread group, which causes workers to stop waiting. In case they are not waiting at the moment, master also sets a bool flag which workers check periodically. However, in C++0x std::thread I don't see any replacement for interrupt(). Do I miss something? If not, how can I implement the above scheme so that workers cannot just sleep forever?

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