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  • C++ data member initializer is not allowed

    - by user1435915
    I totally new to C++ so bear with me. I want to make a class with a static array, and access to this array from the main. Here is what i want to do in C#. namespace ConsoleApplication1 { class Program { static void Main(string[] args) { Class a = new Class(); Console.WriteLine(a.arr[1]); } } } ===================== namespace ConsoleApplication1 { class Class { public static string[] s_strHands = new string[]{"one","two","three"}; } } Here is what i have tried: // justfoolin.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include <string> #include <iostream> using namespace std; class Class { public: static string arr[3] = {"one", "two", "three"}; }; int _tmain(int argc, _TCHAR* argv[]) { Class x; cout << x.arr[2] << endl; return 0; } But i got: IntelliSense: data member initializer is not allowed

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  • C++: calling non-member functions with the same syntax of member ones

    - by peoro
    One thing I'd like to do in C++ is to call non-member functions with the same syntax you call member functions: class A { }; void f( A & this ) { /* ... */ } // ... A a; a.f(); // this is the same as f(a); Of course this could only work as long as f is not virtual (since it cannot appear in A's virtual table. f doesn't need to access A's non-public members. f doesn't conflict with a function declared in A (A::f). I'd like such a syntax because in my opinion it would be quite comfortable and would push good habits: calling str.strip() on a std::string (where strip is a function defined by the user) would sound a lot better than calling strip( str );. most of the times (always?) classes provide some member functions which don't require to be member (ie: are not virtual and don't use non-public members). This breaks encapsulation, but is the most practical thing to do (due to point 1). My question here is: what do you think of such feature? Do you think it would be something nice, or something that would introduce more issues than the ones it aims to solve? Could it make sense to propose such a feature to the next standard (the one after C++0x)? Of course this is just a brief description of this idea; it is not complete; we'd probably need to explicitly mark a function with a special keyword to let it work like this and many other stuff.

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  • Hello world/Console Project in Visual Studio 2008 64 bit

    - by grobartn
    So I am trying to run console 64 bit Hello World program. I have Windows 7 Enterprise x64 bit version. I have installed Visual Studio 2008 and have added all of components needed for 64 bit. I want to create simple console application. It turns out to be a problem. I have simple standard hello world project. I have created it using New Project - Empty project. I added main.cpp that contains this: #include <iostream> using namespace std; int main() { cout << "howdy\n"; } I added new configuration to the project by clicking on Config Manager and added x64 config. Compiled and it compiles. Tried running it and cmd.exe shoots up with following error: "The application has failed to start because its side-by-side configuration is in correct. Please see the application event log or use the command-line sxstrace.e xe tool for more detail. Press any key to continue . . . " Which set-up step if any I am missing. What am I doing wrong and how should I go about setting simple console hello world in 64 bit world. Thanks for any help

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  • Windows/C++: how to use a COM dll which is not registered

    - by Albert
    Hi, In our application, we need to use a COM dll (namely msdia100.dll) which was not registered in the system before. Earler, we have just called the DLL by calling its DllRegisterServer via this code: // Register DIA DLL required by Breakpad std::string diaLibPath = "msdia100"; HMODULE diaLib = LoadLibrary(diaLibPath.c_str()); if( diaLib == NULL ) { errors << "Cannot load DLL " << diaLibPath << endl; return; } typedef HRESULT ( __stdcall * regServer_t )(void); regServer_t regServer = (regServer_t)GetProcAddress(diaLib, "DllRegisterServer"); if( regServer == NULL ) { errors << "Cannot get method DllRegisterServer from " << diaLibPath << endl; FreeLibrary(diaLib); return; } if( regServer() != S_OK ) { errors << "Cannot call DllRegisterServer from " << diaLibPath << endl; } FreeLibrary(diaLib); This doesn't work anymore on Windows 7 (maybe also Vista, didn't tried) because to call this function, it needs Administrator privileges. All solutions to this problem I have found where about getting those Admin rights. That is no possible solution for us because our application must also work if the user is not able to get those Admin rights. It is also no solution for us to suddenly need an installer for our application which registeres this DLL. So, what possibilities are there? How can I use this DLL without Admin rights? Do I have to recode COM which works without the need to register a DLL first?

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  • binary_search not working for a vector<string>

    - by VaioIsBorn
    #include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; int main(void) { string temp; vector<string> encrypt, decrypt; int i,n, co=0; cin >> n; for(i=0;i<n;i++) { cin >> temp; encrypt.push_back(temp); } for(i=0;i<n;i++) { cin >> temp; decrypt.push_back(temp); } for(i=0;i<n;i++) { temp = encrypt[i]; if((binary_search(decrypt.begin(), decrypt.end(), temp)) == true) ++co; } cout << co << endl; return 0; } It reads two equal lists of strings and should print out how many of the words in the first list are also found in the second list, simple. Not giving me the expexted results and i think the problem is in binary_search. Can you tell me why ?

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  • returning opengl display callback in D

    - by Max
    I've written a simple hello world opengl program in D, using the converted gl headers here. My code so far: import std.string; import c.gl.glut; Display_callback display() { return Display_callback // line 7 { return; // just display a blank window }; } // line 10 void main(string[] args) { glutInit(args.length, args); glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE); glutInitWindowSize(800,600); glutCreateWindow("Hello World"); glutDisplayFunc(display); glutMainLoop(); } My problem is with the display() function. glutDisplayFunc() expects a function that returns a Display_callback, which is typedef'd as typedef GLvoid function() Display_callback;. When I try to compile, dmd says line 7: found '{' when expecting ';' following return statement line 10: unrecognized declaration How do I properly return the Display_callback here? Also, how do I change D strings and string literals into char*? My calls to glutInit and glutCreateWindow don't like the D strings they're getting. Thanks for your help.

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  • How to handle 'this' pointer in constructor?

    - by Kyle
    I have objects which create other child objects within their constructors, passing 'this' so the child can save a pointer back to its parent. I use boost::shared_ptr extensively in my programming as a safer alternative to std::auto_ptr or raw pointers. So the child would have code such as shared_ptr<Parent>, and boost provides the shared_from_this() method which the parent can give to the child. My problem is that shared_from_this() cannot be used in a constructor, which isn't really a crime because 'this' should not be used in a constructor anyways unless you know what you're doing and don't mind the limitations. Google's C++ Style Guide states that constructors should merely set member variables to their initial values. Any complex initialization should go in an explicit Init() method. This solves the 'this-in-constructor' problem as well as a few others as well. What bothers me is that people using your code now must remember to call Init() every time they construct one of your objects. The only way I can think of to enforce this is by having an assertion that Init() has already been called at the top of every member function, but this is tedious to write and cumbersome to execute. Are there any idioms out there that solve this problem at any step along the way?

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  • Can C++ do something like an ML case expression?

    - by Nathan Andrew Mullenax
    So, I've run into this sort of thing a few times in C++ where I'd really like to write something like case (a,b,c,d) of (true, true, _, _ ) => expr | (false, true, _, false) => expr | ... But in C++, I invariably end up with something like this: bool c11 = color1.count(e.first)>0; bool c21 = color2.count(e.first)>0; bool c12 = color1.count(e.second)>0; bool c22 = color2.count(e.second)>0; // no vertex in this edge is colored // requeue if( !(c11||c21||c12||c22) ) { edges.push(e); } // endpoints already same color // failure condition else if( (c11&&c12)||(c21&&c22) ) { results.push_back("NOT BICOLORABLE."); return true; } // nothing to do: nodes are already // colored and different from one another else if( (c11&&c22)||(c21&&c12) ) { } // first is c1, second is not set else if( c11 && !(c12||c22) ) { color2.insert( e.second ); } // first is c2, second is not set else if( c21 && !(c12||c22) ) { color1.insert( e.second ); } // first is not set, second is c1 else if( !(c11||c21) && c12 ) { color2.insert( e.first ); } // first is not set, second is c2 else if( !(c11||c21) && c22 ) { color1.insert( e.first ); } else { std::cout << "Something went wrong.\n"; } I'm wondering if there's any way to clean all of those if's and else's up, as it seems especially error prone. It would be even better if it were possible to get the compiler complain like SML does when a case expression (or statement in C++) isn't exhaustive. I realize this question is a bit vague. Maybe, in sum, how would one represent an exhaustive truth table with an arbitrary number of variables in C++ succinctly? Thanks in advance.

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  • Copy constructor called even when returning by reference?

    - by Johnyy
    Hi, I am testing the return of local objects by reference. My original test went well but something else happens unexpected. #include <iostream> using namespace std; class MyInt { public: MyInt(int i){ value = new int(i); } ~MyInt(){ delete value; } int getValue(){ return *value; } MyInt(const MyInt &b){ cout<<"Copy"<<endl; } private: int* value; }; MyInt& returnref(){ MyInt a(10); cout<<"Returning from returnref()"<<endl; return a; } int main(){ MyInt a = returnref(); cout<<a.getValue()<<endl; return 0; } My console prints "Returning from ..." then "Copy" then a random value. My understanding of pass by reference is that it does not need to make any copy. Why is it not doing what I expected?

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  • WSACONNREFUSED when connecting to server

    - by Robert Mason
    I'm currently working on a server. I know that the client side is working (I can connect to www.google.com on port 80, for example), but the server is not functioning correctly. The socket has socket()ed, bind()ed, and listen()ed successfully and is on an accept loop. The only problem is that accept() doesn't seem to work. netstat shows that the server connection is running fine, as it prints the PID of the server process as LISTENING on the correct port. However, accept never returns. Accept just keeps running, and running, and if i try to connect to the port on localhost, i get a 10061 WSACONNREFUSED. I tried looping the connection, and it just keeps refusing connections until i hit ctrl+c. I put a breakpoint directly after the call to accept(), and no matter how many times i try to connect to that port, the breakpoint never fires. Why is accept not accepting connections? Has anyone else had this problem before? Known: [breakpoint0] if ((new_fd = accept(sockint, NULL, NULL)) == -1) { throw netlib::error("Accept Error"); //netlib::error : public std::exception } else { [breakpoint1] code...; } breakpoint0 is reached (and then continued through), no exception is thrown, and breakpoint1 is never reached. The client code is proven to work. Netstat shows that the socket is listening. If it means anything, i'm connecting to 127.0.0.1 on port 5842 (random number). The server is configured to run on 5842, and netstat confirms that the port is correct.

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  • MFC/CCriticalSection: Simple lock situation hangs

    - by raph.amiard
    I have to program a simple threaded program with MFC/C++ for a uni assignment. I have a simple scenario in wich i have a worked thread which executes a function along the lines of : UINT createSchedules(LPVOID param) { genProgThreadVal* v = (genProgThreadVal*) param; // v->searcherLock is of type CcriticalSection* while(1) { if(v->searcherLock->Lock()) { //do the stuff, access shared object , exit clause etc.. v->searcherLock->Unlock(); } } PostMessage(v->hwnd, WM_USER_THREAD_FINISHED , 0,0); delete v; return 0; } In my main UI class, i have a CListControl that i want to be able to access the shared object (of type std::List). Hence the locking stuff. So this CList has an handler function looking like this : void Ccreationprogramme::OnLvnItemchangedList5(NMHDR *pNMHDR, LRESULT *pResult) { LPNMLISTVIEW pNMLV = reinterpret_cast<LPNMLISTVIEW>(pNMHDR); if((pNMLV->uChanged & LVIF_STATE) && (pNMLV->uNewState & LVNI_SELECTED)) { searcherLock.Lock(); // do the stuff on shared object searcherLock.Unlock(); // do some more stuff } *pResult = 0; } The searcherLock in both function is the same object. The worker thread function is passed a pointer to the CCriticalSection object, which is a member of my dialog class. Everything works but, as soon as i do click on my list, and so triggers the handler function, the whole program hangs indefinitely.I tried using a Cmutex. I tried using a CSingleLock wrapping over the critical section object, and none of this has worked. What am i missing ?

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  • gcc -finline-functions behaviour?

    - by user176168
    I'm using gcc with the -finline-functions optimization for release builds. In order to combat code bloat because I work on an embedded system I want to say don't inline particular functions. The obvious way to do this would be through function attributes ie attribute(noinline). The problem is this doesn't seem to work when I switch on the global -finline-functions optimisation which is part of the -O3 switch. It also has something to do with it being templated as a non templated version of the same function doesn't get inlined which is as expected. Has anybody any idea of how to control inlining when this global switch is on? Here's the code: #include <cstdlib> #include <iostream> using namespace std; class Base { public: template<typename _Type_> static _Type_ fooT( _Type_ x, _Type_ y ) __attribute__ (( noinline )); }; template<typename _Type_> _Type_ Base::fooT( _Type_ x, _Type_ y ) { asm(""); return x + y; } int main(int argc, char *argv[]) { int test = Base::fooT( 1, 2 ); printf( "test = %d\n", test ); system("PAUSE"); return EXIT_SUCCESS; }

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  • [C++] My First Go With Function Templates

    - by bobber205
    Thought it was pretty straight forward. But I get a "iterator not dereferencable" errro when running the below code. What's wrong? template<typename T> struct SumsTo : public std::binary_function<T, T, bool> { int myInt; SumsTo(int a) { myInt = a; } bool operator()(const T& l, const T& r) { cout << l << " + " << r; if ((l + r) == myInt) { cout << " does add to " << myInt; } else { cout << " DOES NOT add to " << myInt; } return true; } }; void main() { list<int> l1; l1.push_back(1); l1.push_back(2); l1.push_back(3); l1.push_back(4); list<int> l2; l2.push_back(9); l2.push_back(8); l2.push_back(7); l2.push_back(6); transform(l1.begin(), l1.end(), l2.begin(), l2.end(), SumsTo<int>(10) ); }

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  • STL vector performance

    - by iAdam
    STL vector class stores a copy of the object using copy constructor each time I call push_back. Wouldn't it slow down the program? I can have a custom linkedlist kind of class which deals with pointers to objects. Though it would not have some benefits of STL but still should be faster. See this code below: #include <vector> #include <iostream> #include <cstring> using namespace std; class myclass { public: char* text; myclass(const char* val) { text = new char[10]; strcpy(text, val); } myclass(const myclass& v) { cout << "copy\n"; //copy data } }; int main() { vector<myclass> list; myclass m1("first"); myclass m2("second"); cout << "adding first..."; list.push_back(m1); cout << "adding second..."; list.push_back(m2); cout << "returning..."; myclass& ret1 = list.at(0); cout << ret1.text << endl; return 0; } its output comes out as: adding first...copy adding second...copy copy The output shows the copy constructor is called both times when adding and when retrieving the value even then. Does it have any effect on performance esp when we have larger objects?

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  • Is there a reason why SSIS significantly slows down after a few minutes?

    - by Mark
    I'm running a fairly substantial SSIS package against SQL 2008 - and I'm getting the same results both in my dev environment (Win7-x64 + SQL-x64-Developer) and the production environment (Server 2008 x64 + SQL Std x64). The symptom is that initial data loading screams at between 50K - 500K records per second, but after a few minutes the speed drops off dramatically and eventually crawls embarrasingly slowly. The database is in Simple recovery model, the target tables are empty, and all of the prerequisites for minimally logged bulk inserts are being met. The data flow is a simple load from a RAW input file to a schema-matched table (i.e. no complex transforms of data, no sorting, no lookups, no SCDs, etc.) The problem has the following qualities and resiliences: Problem persists no matter what the target table is. RAM usage is lowish (45%) - there's plenty of spare RAM available for SSIS buffers or SQL Server to use. Perfmon shows buffers are not spooling, disk response times are normal, disk availability is high. CPU usage is low (hovers around 25% shared between sqlserver.exe and DtsDebugHost.exe) Disk activity primarily on TempDB.mdf, but I/O is very low (< 600 Kb/s) OLE DB destination and SQL Server Destination both exhibit this problem. To sum it up, I expect either disk, CPU or RAM to be exhausted before the package slows down, but instead its as if the SSIS package is taking an afternoon nap. SQL server remains responsive to other queries, and I can't find any performance counters or logged events that betray the cause of the problem. I'll gratefully reward any reasonable answers / suggestions.

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  • What limits scaling in this simple OpenMP program?

    - by Douglas B. Staple
    I'm trying to understand limits to parallelization on a 48-core system (4xAMD Opteron 6348, 2.8 Ghz, 12 cores per CPU). I wrote this tiny OpenMP code to test the speedup in what I thought would be the best possible situation (the task is embarrassingly parallel): // Compile with: gcc scaling.c -std=c99 -fopenmp -O3 #include <stdio.h> #include <stdint.h> int main(){ const uint64_t umin=1; const uint64_t umax=10000000000LL; double sum=0.; #pragma omp parallel for reduction(+:sum) for(uint64_t u=umin; u<umax; u++) sum+=1./u/u; printf("%e\n", sum); } I was surprised to find that the scaling is highly nonlinear. It takes about 2.9s for the code to run with 48 threads, 3.1s with 36 threads, 3.7s with 24 threads, 4.9s with 12 threads, and 57s for the code to run with 1 thread. Unfortunately I have to say that there is one process running on the computer using 100% of one core, so that might be affecting it. It's not my process, so I can't end it to test the difference, but somehow I doubt that's making the difference between a 19~20x speedup and the ideal 48x speedup. To make sure it wasn't an OpenMP issue, I ran two copies of the program at the same time with 24 threads each (one with umin=1, umax=5000000000, and the other with umin=5000000000, umax=10000000000). In that case both copies of the program finish after 2.9s, so it's exactly the same as running 48 threads with a single instance of the program. What's preventing linear scaling with this simple program?

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  • SFINAE + sizeof = detect if expression compiles

    - by FredOverflow
    I just found out how to check if operator<< is provided for a type. template<class T> T& lvalue_of_type(); template<class T> T rvalue_of_type(); template<class T> struct is_printable { template<class U> static char test(char(*)[sizeof( lvalue_of_type<std::ostream>() << rvalue_of_type<U>() )]); template<class U> static long test(...); enum { value = 1 == sizeof test<T>(0) }; typedef boost::integral_constant<bool, value> type; }; Is this trick well-known, or have I just won the metaprogramming Nobel prize? ;) EDIT: I made the code simpler to understand and easier to adapt with two global function template declarations lvalue_of_type and rvalue_of_type.

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  • Solved: Help with this compile error

    - by Scott
    I just picked up an old project and I'm not sure what the following error could mean. g++ -o BufferedReader.o -c -g -Wall -std=c++0x -I/usr/include/xmms2 -Ijsoncpp/include/json/ -fopenmp -I/usr/include/ImageMagick -I/usr/include/xmms2 -I/usr/include/libvisual-0.4 -D_GNU_SOURCE=1 -D_REENTRANT -I/usr/include/SDL -DQT_CORE_LIB -DQT_GUI_LIB -DQT_SCRIPT_LIB -DQT_SHARED -I/usr/include/QtCore -I/usr/include/QtGui -I/usr/include/QtScript BufferedReader.cpp In file included from BufferedReader.cpp:23: /usr/include/string.h:36:42: error: missing binary operator before token "(" In file included from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/cwchar:47, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/bits/postypes.h:42, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/iosfwd:42, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/ios:39, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/istream:40, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/sstream:39, from BufferedReader.cpp:24: At line 24 of BufferedReader.cpp is #include <string.h>. I've tried it with just <string> but get the same thing. Any clue? Here's the snippet of code from string.h /* Tell the caller that we provide correct C++ prototypes. */ #if defined __cplusplus && __GNUC_PREREQ (4, 4) //line 36 # define __CORRECT_ISO_CPP_STRING_H_PROTO #endif Does that mean __GNUC_PREREQ isn't defined? Edit: Changing -Ijsoncpp/include/json/ to Ijsoncpp/include stopped the errors. I noticed I was including <json/json.h>. I'm about to switch to JsonGlib though, which is the reason I pulled the project up again. So it's all good. :)

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  • Problem with passing vector of pointers to objects to member function of another object

    - by Jamesz
    Hi, I have a vector of pointers to Mouse objects called 'mice'. I'm passing the mice to the cat by reference. vector <Mouse*> mice; Cat * c; c->lookForMouse(&mice); And here's my lookForMouse() member function void Cat::lookForMouse(vector <Mouse*> *mice) { ... } And now to the problem! Within the function above, I can't seem to access my mice. This below will not work mice[i]->isActive(); The error message I receive suggests to use mice[i].isActive(), but this throws an error saying isActive() is not a member of std::vector<_Ty ... This works though... vector <Mouse*> miceCopy = *mice; miceCopy[i]->isActive(); I understand that I shouldn't be creating another vector of mice here, it defeats the whole point of passing it by reference (let me know if I'm wrong)... Why can't I do mice[i]-isActive() What should I be doing? Thanks for your time and help :D James.

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  • Path String Combination Question.

    - by Nano HE
    Hi. Please see my code below. ifstream myLibFile ("libs//%s" , line); // Compile failed here ??? I want to combine the path string and open the related file again. #include <iostream> #include <fstream> #include <string> using namespace std; int main () { string line; ifstream myfile ("libs//Config.txt"); // There are several file names listed in the COnfig.txt file line by line. if (myfile.is_open()) { while (! myfile.eof() ) { getline (myfile,line); cout << line << endl; // Read details lib files based on the each line file name. string libFileLine; ifstream myLibFile ("libs//%s" , line); // Compile failed here ??? if (myLibFile.is_open()) { while (! myLibFile.eof() ) { print "success"; } myLibFile.close(); } } myfile.close(); } else cout << "Unable to open file"; return 0; }

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  • Callback function and function pointer trouble in C++ for a BST

    - by Brendon C.
    I have to create a binary search tree which is templated and can deal with any data types, including abstract data types like objects. Since it is unknown what types of data an object might have and which data is going to be compared, the client side must create a comparison function and also a print function (because also not sure which data has to be printed). I have edited some C code which I was directed to and tried to template, but I cannot figure out how to configure the client display function. I suspect variable 'tree_node' of class BinarySearchTree has to be passed in, but I am not sure how to do this. For this program I'm creating an integer binary search tree and reading data from a file. Any help on the code or the problem would be greatly appreciated :) Main.cpp #include "BinarySearchTreeTemplated.h" #include <iostream> #include <fstream> #include <string> using namespace std; /*Comparison function*/ int cmp_fn(void *data1, void *data2) { if (*((int*)data1) > *((int*)data2)) return 1; else if (*((int*)data1) < *((int*)data2)) return -1; else return 0; } static void displayNode() //<--------NEED HELP HERE { if (node) cout << " " << *((int)node->data) } int main() { ifstream infile("rinput.txt"); BinarySearchTree<int> tree; while (true) { int tmp1; infile >> tmp1; if (infile.eof()) break; tree.insertRoot(tmp1); } return 0; } BinarySearchTree.h (a bit too big to format here) http://pastebin.com/4kSVrPhm

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  • C++: defining maximum/minimum limits for a class

    - by Luis
    Basically what the title says... I have created a class that models time slots in a variable-granularity daily schedule (where for example the first time slot is 30 minutes, but the second time slot can be 40 minutes); the first available slot starts at (a value comparable to) 1. What I want to do now is to define somehow the maximum and minimum allowable values that this class takes and I have two practical questions in order to do so: 1.- does it make sense to define absolute minimum and maximum in such a way for a custom class? Or better, does it suffice that a value always compares as lower-than any other possible value of the type, given the class's defined relational operators, to be defined the min? (and analogusly for the max) 2.- assuming the previous question has an answer modeled after "yes" (or "yes but ..."), how do I define such max/min? I know that there is std::numeric_limits<> but from what I read it is intended for "numeric types". Do I interpret that as meaning "represented as a number" or can I make a broader assumption like "represented with numbers" or "having a correspondence to integers"? After all, it would make sense to define the minimum and maximum for a date class, and maybe for a dictionary class, but numeric_limits may not be intended for those uses (I don't have much experience with it). Plus, numeric_limits has a lot of extra members and information that I don't know what to make with. If I don't use numeric_limits, what other well-known / widely-used mechanism does C++ offer to indicate the available range of values for a class?

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  • C++ design related question

    - by Kotti
    Hi! Here is the question's plot: suppose I have some abstract classes for objects, let's call it Object. It's definition would include 2D position and dimensions. Let it also have some virtual void Render(Backend& backend) const = 0 method used for rendering. Now I specialize my inheritance tree and add Rectangle and Ellipse class. Guess they won't have their own properties, but they will have their own virtual void Render method. Let's say I implemented these methods, so that Render for Rectangle actually draws some rectangle, and the same for ellipse. Now, I add some object called Plane, which is defined as class Plane : public Rectangle and has a private member of std::vector<Object*> plane_objects; Right after that I add a method to add some object to my plane. And here comes the question. If I design this method as void AddObject(Object& object) I would face trouble like I won't be able to call virtual functions, because I would have to do something like plane_objects.push_back(new Object(object)); and this should be push_back(new Rectangle(object)) for rectangles and new Circle(...) for circles. If I implement this method as void AddObject(Object* object), it looks good, but then somewhere else this means making call like plane.AddObject(new Rectangle(params)); and this is generally a mess because then it's not clear which part of my program should free the allocated memory. ["when destroying the plane? why? are we sure that calls to AddObject were only done as AddObject(new something).] I guess the problems caused by using the second approach could be solved using smart pointers, but I am sure there have to be something better. Any ideas?

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  • returning reference to a vector from a method and using its public members

    - by memC
    dear experts, I have a vector t_vec that stores references to instances of class Too. The code is shown below. In the main , I have a vector t_vec_2 which has the same memory address as B::t_vec. But when I try to access t_vec_2[0].val1 it gives error val1 not declared. Could you please point out what is wrong? Also, if you know of a better way to return a vector from a method, please let me know! Thanks in advance. class Too { public: Too(); ~Too(){}; int val1; }; Too::Too(){ val1 = 10; }; class B { public: vector<Too*> t_vec; Too* t1; vector<Too*>& get_tvec(); B(){t1 = new Too();}; ~B(){delete t1;}; }; vector<Too*>& B::get_tvec(){ t_vec.push_back(t1); return t_vec; } int main(){ B b; b = B(); vector<Too*>& t_vec_2 = b.get_tvec(); // Getting error std::cout << "\n val1 = " << t_vec_2[0].val1; return 0; }

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  • Why does double dispatch not work in C++?

    - by Bruce
    #include<iostream.h> #include<conio.h> using namespace std; class SpaceShip {}; class GiantSpaceShip : public SpaceShip {}; class Asteroid { public: virtual void CollideWith(SpaceShip *) { cout << "Asteroid hit a SpaceShip" << endl; } virtual void CollideWith(GiantSpaceShip *) { cout << "Asteroid hit a GiantSpaceShip" << endl; } }; class ExplodingAsteroid : public Asteroid { public: virtual void CollideWith(SpaceShip *) { cout << "ExplodingAsteroid hit a SpaceShip" << endl; } virtual void CollideWith(GiantSpaceShip *) { cout << "ExplodingAsteroid hit a GiantSpaceShip" << endl; } }; int main() { SpaceShip * s = new GiantSpaceShip(); Asteroid * a = new ExplodingAsteroid(); a->CollideWith(s); getch(); return 0; } How can I enable double dispatch in C++?

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