c++

fold expression and function name lookup

由 落爺英雄遲暮 提交于 2021-02-20 19:58:35
问题 I am learning fold expressions in C++17. I have the following code #include <iostream> #include <vector> namespace io { template<typename T> std::istream &operator>>(std::istream &in, std::vector<T> &vec) { for (auto &x : vec) in >> x; return in; } template<class... Args> void scan(Args &... args) { (std::cin >> ... >> args); } }// namespace io int main() { std::vector<int> s(1), t(1); io::scan(s, t); std::cout << s[0] << ' ' << t[0] << '\n'; } Using GCC 9.3.0, the code compiles and runs

c++ (1) c++ 与c 的区别

由 吃可爱长大的小学妹 提交于 2021-02-20 19:47:19
可以说c++ 语言在c基础上扩展了许多 在学习玩c语言之后 学习c++ 会发现容易一些 但是c++也有优越于c 的地方 c++ 与c 语言都属于本地编译型语言 ，直接编译成本地编译码，运行特别快。 c++ OPP 面向对象语言 区别于 java python PHP 脚本（解释性）语言 后者必须要具备脚本解释器，运行在本地操作系统上 因此c与c++ 的区别 总结以下 1） c++ 支持带默认参数 1 函数形参给默认值 ，从右向左给 void fun （int a,int b=10) ✅ void fun (int a=10,int b)❌ 2 函数形参可以在声明的时候给 也可以在定义的时候给 3 调用一个带默认值的函数与一个不带默认值的函数在效率上具有区别 int sum( int a = 10 , int b = 20 ); int sum( int a, int b) { return a + b; } int main() { sum( 10 , 10 ); 00FE142E push 0Ah 00FE1430 push 0Ah 00FE1432 call sum(0FE105Fh) 00FE1437 add esp, 8 sum(); 00FE143A push 14h 00FE143C push 0Ah 00FE143E call sum(0FE105Fh)

Callback from C++ to C# using SWIG

由 霸气de小男生 提交于 2021-02-20 19:23:31
问题 I have an application running in C#.Netcore and C++ windows application. I achieved interoperability between C# & C++ using SWIG. But I am not able to achieve Callback functionality from C++ to C#. Also I tried by passing function pointer from C# to C++. But it also failed My Intention is to achieve callback by By passing a C# function pointer to C++ and call that function pointer when needed so that C# function will be executed. Creating a base class with virtual function in C++ and derive a

Callback from C++ to C# using SWIG

由 喜你入骨 提交于 2021-02-20 19:22:11
问题 I have an application running in C#.Netcore and C++ windows application. I achieved interoperability between C# & C++ using SWIG. But I am not able to achieve Callback functionality from C++ to C#. Also I tried by passing function pointer from C# to C++. But it also failed My Intention is to achieve callback by By passing a C# function pointer to C++ and call that function pointer when needed so that C# function will be executed. Creating a base class with virtual function in C++ and derive a

What is the order of constructor call in virtual inheritance?

由 China☆狼群 提交于 2021-02-20 19:15:12
问题 What is the order of constructor call in virtual inheritance in c++? For the following two cases of multiple inheritance; (I) for the following code, without virtual inheritance; class a { public: a() { cout<<"\t a"; } }; class b: public a { public: b() { cout<<"\t b"; } }; class c: public b { public: c() { cout<<"\t c"; } }; class d: public c { public: d() { cout<<"\t d"; } }; class e: public c, public d { public: e() { cout<<"\t e"; } }; class f: public b, public e { public: f() { cout<<"\t

Is it safe to compare boolean variable with 1 and 0 in C, C++? [duplicate]

由 守給你的承諾、 提交于 2021-02-20 19:13:19
问题 This question already has answers here : Can I assume (bool)true == (int)1 for any C++ compiler? (4 answers) Closed 6 years ago . Consider the code bool f() { return 42; } if (f() == 1) printf("hello"); Does C (C99+ with stdbool.h) and C++ standards guarantee that "hello" will printed? Does bool a = x; is always equivalent to bool a = x ? 1 : 0; 回答1: In C++, bool is a built-in type. Conversions from any type to bool always yield false (0) or true (1). Prior to the 1999 ISO C standard, C did

Visual C++ Exception not shown in console

由 本小妞迷上赌 提交于 2021-02-20 19:03:21
问题 I've implemented a C++ Exception and throw this exception on errors without catching it. In linux I do see the exception text ("what") on console and the application exists. This is my expected behaviour. On windows (compiled with Visual C++ 2015) however a popup window opens and states a generic error. I do not see the exception message on console or anywhere else. Is it possible to log thrown/uncaught exceptions to console/stdout (or stderr) on Windows, too? Thank you 回答1: Throwing an

LogonUser returns true for a wrong password

由 时光怂恿深爱的人放手 提交于 2021-02-20 19:02:29
问题 bool bRet=LogonUser(strUserName, L"", strPassword, LOGON32_LOGON_TYPE_NEW_CREDENTIALS, LOGON32_PROVIDER_WINNT50, &phToken) bRet always returns true even if I enter a wrong password when there is no domain. Is there any work around like if I enter a valid password it returns true and false for a wrong password when there is no domain. 回答1: I assume that by LOGON32_LOGON_TYPE_NEW_CREDENTIALS you actually mean LOGON32_LOGON_NEW_CREDENTIALS . In which case the behaviour is exactly as would be

Private aggregate initialization

由 元气小坏坏 提交于 2021-02-20 19:02:13
问题 Is it possible to define as private the aggregate initialization for an aggregate class? I would like that the class can only be aggregate-initialized by its own static private members. Example: struct Size { const unsigned int width; const unsigned int height; static const Size big; static const Size small; private: Size( ) = default; // something to declare the aggregare initialization as private }; const Size Size::big = { 480, 240 }; const Size Size::small = { 210, 170 }; 来源： https:/

Writing video with openCV - no key frame set for track 0

由 左心房为你撑大大i 提交于 2021-02-20 16:46:47
问题 I'm trying to modify and write some video using openCV 2.4.6.1 using the following code: cv::VideoCapture capture( video_filename ); // Check if the capture object successfully initialized if ( !capture.isOpened() ) { printf( "Failed to load video, exiting.\n" ); return -1; } cv::Mat frame, cropped_img; cv::Rect ROI( OFFSET_X, OFFSET_Y, WIDTH, HEIGHT ); int fourcc = static_cast<int>(capture.get(CV_CAP_PROP_FOURCC)); double fps = 30; cv::Size frame_size( RADIUS, (int) 2*PI*RADIUS ); video
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