std

问题 I have a map of pointer to member declared as : std::map<char, T (Operand::*)(const T &, const T &)> op_map; I fill my map with pointer to member directly in the constructor of my class with : op_map['+'] = &Operand::op_add; For example, op_add source code is : T op_add(const T & a, const T & b) { return a + b; } And I want to call my pointer to member from a const function. Here is the source code : IOperand *res_int32(char op, const IOperand & rhs) const { IOperand *res = const_cast

问题 This is a convenient way to define a subclass of ostream that sets a buffer (MyStreamBuf is some subclass of std::streambuf): class MyOStream : public std::ostream { public: MyOStream(): std::ostream(&buffer) {} // ... private: MyStreamBuffer buffer; }; Here std::ostream's constructor is called before the constructor of buffer, so the streambuf* being passed in is pointing to an unconstructed object that has virtual methods. The same issue applies in ~MyStream(), as buffer is destructed

问题 I have the following code: float x1 = 0,x2 = 0,y1 = 0,y2 = 0; cout << "Enter coordinates as \"(x1,y1) (x2,y2)\"\n"; cin >> x1; cin.ignore(1, ','); cin >> y1; cin >> x2; cin.ignore(1, ','); cin >> y2; cout << "Coordinates registered as (" << x1 << "," << y1 << "), (" << x2 << "," << y2 << ").\n"; But this always returns (0,0) (0,0). What would the correct implementation of cin.ignore be? 回答1: If you are literally entering in the data in the form of (x1,y1) (x2,y2) like (10,20) (30,40) Then you

问题 ---Answered --> Make the operator functions const! I am writing a template and keep getting the following error: Error 1 error C2893: Failed to specialize function template 'unknown-type std::less::operator ()(_Ty1 &&,_Ty2 &&) const' when trying to use the template with a class, even if the class has overloaded operators. Note that the template does work with primitives ____TEMPLATE_________ #include <vector> #include <algorithm> using namespace std; template <class T> class Set{ int elements

问题 I have been having problems making a C++ Test Project work in Visual Studio 2010. I am looking for what is wrong/what to do about it. This kind of test project has to be compiled as managed code. No problem. C++ can be built that way. I did it this trivial example std::list example. I created a C++ CLR project. I pasted this code in and compiled. I can step through the code as it runs. It works. #include "stdafx.h" #include <list> using namespace System; int main(array<System::String ^> ^args

问题 Is it possible to add elements to stdclasses like we do for arrays? Array ( [0] => item 1 [1] => item 2 ) Stdclass ( [0] => item 1 [1] => item 2 ) Is it generally harder to manipulate objects as compared to arrays? Since we have lots of array functions to make use of etc. 回答1: Sure, you can add new elements... $Object = new StdClass(); $Object->item1 = 1; $Object->item2 = 2; If you want to iterate object as array you should use PHP SPL ArrayIterator or RecursiveArrayIterator. Also you can use

问题 I'm trying to apply file's extension filters to the file's selection dialog. This way works: ofn.lpstrFilter = "(*.exe) Windows Executable\0*.exe\0" "(*.ini) Windows Initialization file \0*.ini\0" "(*.dll) Dynamic Link Library \0*.dll\0" "(*.lib) Windows Library file \0*.lib\0" "(*.conf) Windows Configuration file \0*.conf\0"; But when I'm assigning extension filters dynamically, via parameters, it fails, filters don't appear in the combo box: LPCSTR filter = (LPCSTR)extFilter; //Contains

问题 I'm wondering why the following piece of code doesn't work, looks pretty straight-forward, am I making a mistake? The result of this is: file created but empty, if I manually add lines those lines are showed with this code, but nothing else happens. #include <fstream> #include <iostream> #include <string> using namespace std; int main(){ fstream mfile("text.txt", ios_base::in | ios_base::out | ios_base::app); mfile.seekg(ios_base::beg); string line; while( getline(mfile,line) ){ std::cout <<

问题 I need to parse a txt file, from disk. So i have firstly made an example, to test regex. This is my example code: std::string txt("paragraph:\r\nthis is the text file\r\ni need only this data\r\nnotthis"); std::smatch m; std::regex rt("paragraph:([\\S\\s](?=notthis))"); std::regex_search(txt, m, rt); std::cout << m.str(1) << std::endl; So i'm trying to parse until notthis , but returned match m is a failed match. If i do the regex like this: std::regex rt("paragraph:([\\S\\s]+)"); it works

问题 I created a read only iterator which allows me to use it in a for loop more conveniently then with the std iterators, similar to what boost does with the FOREACH (not as good but good enough :)) Now it looks like this: for(ReadOnylIterator<MyClass *> class = parent.getIterator(); class.end(); ++class) class->function(); The problem that I have now is, that I must implement a function on the parent which returns the iterator. Since the std containers have all the same syntax, I was wondering