operators

问题 I am trying to add 2 complex numbers together, but i am getting the errors: no operator "+" matches these operands no operator "<<" matches these operands #include <iostream> using namespace std; class complex { public: double get_r() { return r; } void set_r(double newr) { r=newr; } double set_i() { return i; } void set_i(double newi) { i = newi; } private: double r, i; }; int main() { complex A, B; A.set_r(1.0); A.set_i(2.0); B.set_r(3.0); B.set_i(2.0); complex sum = A+B; cout << "summen er

问题 I have a key type: struct KeyT { uint32_t timestamp; // example! uint32_t a; uint32_t b; uint32_t c; uint32_t d; uint32_t e; // ... bool operator== (const KeyT& key) const { if(timestamp == key.timestamp && a == key.a && b == key.b && d == key.d && c == key.c && e == key.e) return true; return false; } bool operator< (const KeyT& key) const { if(timestamp < key.timestamp) return true; else if(timestamp == key.timestamp && a < key.a && b < key.b && c < key.c && d < key.d && e < key.e) return

问题 Consider the following statements: int? v1 = null; int? v2 = 5 * v1; What is the value of v2 ? ( null or empty string?) How can I prevent the compiler to mark it as invalid operation? Do I need to follow custom exception handling? 回答1: It's null . C# Language Specification 3.0 (Section §7.2.7: Lifted operators) For the binary operators + - * / % & | ^ << >> : a lifted form of an operator exists if the operand and result types are all non-nullable value types. The lifted form is constructed by

问题 Consider the following statements: int? v1 = null; int? v2 = 5 * v1; What is the value of v2 ? ( null or empty string?) How can I prevent the compiler to mark it as invalid operation? Do I need to follow custom exception handling? 回答1: It's null . C# Language Specification 3.0 (Section §7.2.7: Lifted operators) For the binary operators + - * / % & | ^ << >> : a lifted form of an operator exists if the operand and result types are all non-nullable value types. The lifted form is constructed by

问题 I'm new to PHP and I'm confused seeing some examples calling a function with a @ prefix like @mysql_ping(). What is it for? Googling / searching is not much of a help since @ gets discarded and 'alias' is not good enough keyword. 回答1: @ suppresses errors, warnings and notices. You can use it for good purpose if you complement it with a custom error handler or with due check of $php_errormsg variable so you can handle errors properly. In my experience, this proper usage is not seen very much

问题 Just gonna warn you, I'm brand new to swift and I'm still getting used to how this works. I've been trying to work on this Calculator project for class. The problem is, I need practice simplifying code. Right now, when a number button is pressed, I have it saved in an array like this. @IBAction func buttonPressed(_ sender: UIButton) { if numBtnPressed == true { numArray.append(sender.title(for: .normal)!) } } so if the button labeled 1 is pressed, it stores ["1"] as a string in the empty

问题 Why does (Not 1) evaluate as -2? I would expect it to evaluate as 0. 回答1: VBA/VBScript does not have real logical operators (AND, OR, NOT). The logical operators you see are actually bitwise operators, and that's all you get. VBA plays some games with the True and False values so this works most of the time, but occasionally you'll find a "gotcha". In this case, instead of If Not InStr() Then you have to write If InStr() <= 0 Then . Instead of If InStr() Then you have to write If InStr() > 0

问题 While reading Discovering modern C++ by Peter Gottschling I found out that there is a new operator in c++11 named sizeof... . What's the usage of it? I could find only one reference about it over internet in cppreference. Edit: This is sizeof... operator not sizeof . Added this as a question here, as it was very difficult to get info about this operator during search. And hoping users will get the answer easier with this. 来源： https://stackoverflow.com/questions/59693407/whats-the-use-of

问题 I want to use reflection and do either an implicit or explicit coversion using reflection. Given I have defined Foo this way public class Foo { public static explicit operator decimal(Foo foo) { return foo.Value; } public static explicit operator Foo(decimal number) { return new Foo(number); } public Foo() { } public Foo(decimal number) { Value = number; } public decimal Value { get; set; } public override string ToString() { return Value.ToString(); } } When I run this code decimal

问题 Consider the following MCVE, where I have two value arrays where w is two times v (try it out here): #include <valarray> using namespace std; int main() { valarray<int> v { 1, 2, 3 }; for ([[maybe_unused]] auto x : v) {} // Ok auto w = v * 2; // Leads to failure in loop below //valarray<int> w = v * 2; // Works //auto w = v*=2; // Works //auto w = v; w *= 2; // Works for ([[maybe_unused]] auto x : w) {} // Failure here } This example fails to compile with clang and gcc at the last loop with