operator-keyword

问题 If I've overloaded operator+ and operator= do I still need to overload operator+= for something like this to work: MyClass mc1, mc2; mc1 += mc2; 回答1: operator+= is not a composite of + and =, therefore you do need to overload it explicitly, since compiler do not know to build puzzles for you. but still you do able to benefit from already defined/overloaded operators, by using them inside operator+=. 回答2: Yes, you need to define that as well. A common trick however, is to define operator+= ,

问题 Will the differences below matter significantly in C#? int a, b; double result; result = (double)a / b; result = a / (double)b; result = (double)a / (double)b; Which one do you use? 回答1: The cast will occur before the division. In your examples, it doesn't matter which one you do as if one operand is a double, the runtime will cast/convert the other to a double as well. This looks like a micro-optimization - not something worth worrying about or dealing with unless measurements show it is

问题 In order to implement auto-vivification of Ruby hash, one can employ the following class class AutoHash < Hash def initialize(*args) super() @update, @update_index = args[0][:update], args[0][:update_key] unless args.empty? end def [](k) if self.has_key?k super(k) else AutoHash.new(:update => self, :update_key => k) end end def []=(k, v) @update[@update_index] = self if @update and @update_index super end def few(n=0) Array.new(n) { AutoHash.new } end end This class allows to do the following

问题 In order to implement auto-vivification of Ruby hash, one can employ the following class class AutoHash < Hash def initialize(*args) super() @update, @update_index = args[0][:update], args[0][:update_key] unless args.empty? end def [](k) if self.has_key?k super(k) else AutoHash.new(:update => self, :update_key => k) end end def []=(k, v) @update[@update_index] = self if @update and @update_index super end def few(n=0) Array.new(n) { AutoHash.new } end end This class allows to do the following

问题 Forgive me, for I am fairly new to C++, but I am having some trouble regarding operator ambiguity. I think it is compiler-specific, for the code compiled on my desktop. However, it fails to compile on my laptop. I think I know what's going wrong, but I don't see an elegant way around it. Please let me know if I am making an obvious mistake. Anyhow, here's what I'm trying to do: I have made my own vector class called Vector4 which looks something like this: class Vector4 { private: GLfloat

问题 Let's say we have this class A: class A { public: int a; A(int b) { a = b; } }; I would like to create a + overload such that I could use it like this A a(1),b(2),c(3),&d; d = a + b + c; without modifying the content of each object. The next logical thing would be allocating a new chunk of memory each time like this: A &operator+ (const A &b) { A *c = new A(a+b.a); return *c; } But this would create a new problem: intermediate results are lost, causing memory leaks. I could have easily solved

问题 This question already has answers here : What's the purpose of the + (pos) unary operator in Python? (6 answers) Closed 3 years ago . So I have a simple piece of code that prints out the integers 1-10: i = 0 while i < 10: i += 1 print(i) Then if you just change one operator around on line 3, it prints out an infinite amount of 1 integers(which i understand why it does that). Why isn't a syntax error occurring when running this second program? Wouldn't it call a syntax error in the event of an

问题 I'm trying to develop an Android App which shows the signal strength of various network operators on a map. The problem is that the only way to change the network operator is by doing it by hand. Any ideas on how I can get this information without changing it manually? I think that there are internal/private Android classes to do this. 回答1: You will need to use one or more of Google's internal APIs to do this. They are not, by default, available to Android applications for various (usually

问题 I have the following code: class A { public: operator int() const { return 5; } }; class B { public: operator int() const { return 6; } }; int main() { A a; B b; int myInt = true ? a : b; return 0; } Attempting to compile that code with Visual Studio 2017 RC results in the following error: error C2446 : : : no conversion from B to A note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called ...which is surprising because I would

问题 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? EDIT: The meaning of < can be assumed so as to guarantee uniqueness as long as any of the fields are unequal. EDIT 2: A simplistic implementation: bool Class1::operator<