operator-keyword | 易学教程

Operator Overloading in C++ as int + obj

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问题 I have following class:- class myclass { size_t st; myclass(size_t pst) { st=pst; } operator int() { return (int)st; } int operator+(int intojb) { return int(st) + intobj; } }; this works fine as long as I use it like this:- char* src=\"This is test string\"; int i= myclass(strlen(src)) + 100; but I am unable to do this:- int i= 100+ myclass(strlen(src)); Any idea, how can I achieve this?? 回答1: Implement the operator overloading outside of the class: class Num { public: Num(int i) { this->i =

Strange Java behaviour. Ternary operator

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问题 Why does this code work? Float testFloat = null; Float f = true ? null : 0f; And why does this throw an exception? Float testFloat = null; Float f = true ? testFloat : 0f; But the strangest thing is that this code also runs successfully without any exceptions: Float testFloat = null; Float f = testFloat; It seems that the ternary operator of Java changes the behaviour. Can anyone explain why this is, please? 回答1: The behaviour is specified in JLS - Conditional Operator: If one of the second

Trouble with inheritance of operator= in C++

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问题 I\'m having trouble with the inheritance of operator=. Why doesn\'t this code work, and what is the best way to fix it? #include <iostream> class A { public: A & operator=(const A & a) { x = a.x; return *this; } bool operator==(const A & a) { return x == a.x; } virtual int get() = 0; // Abstract protected: int x; }; class B : public A { public: B(int x) { this->x = x; } int get() { return x; } }; class C : public A { public: C(int x) { this->x = x; } int get() { return x; } }; int main() { B

How are Python in-place operator functions different than the standard operator functions?

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问题 Why isn\'t operator.iadd(x, y) equivalent to z = x; z += y ? And how does operator.iadd(x, y) differ from operator.add(x, y) ? From the docs: Many operations have an “in-place” version. The following functions provide a more primitive access to in-place operators than the usual syntax does; for example, the statement x += y is equivalent to x = operator.iadd(x, y). Another way to put it is to say that z = operator.iadd(x, y) is equivalent to the compound statement z = x; z += y. Related

How != and == operators work on Integers in Java? [duplicate]

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问题 This question already has answers here : Why is 128==128 false but 127==127 is true when comparing Integer wrappers in Java? (6 answers) Closed 3 years ago . The following code seemed really confusing to me since it provided two different outputs.The code was tested on jdk 1.7. public class NotEq { public static void main(String[] args) { ver1(); System.out.println(); ver2(); } public static void ver1() { Integer a = 128; Integer b = 128; if (a == b) { System.out.println(\"Equal Object\"); }

Python's Logical Operator AND

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问题 I\'m a little confused with the results I\'m getting with the logical operators in Python. I\'m a beginner and studying with the use of a few books, but they don\'t explain in as much detail as I\'d like. here is my own code: five = 5 two = 2 print five and two >> 2 It seems to be just outputting the two variable. five = 5 two = 2 zero = 0 print five and two and zero So, I added another variable integer. Then I printed and got the following output: >> 0 What is going on with Python in the

Using == operator in Java to compare wrapper objects

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问题 I\'m reading SCJP Java 6 by Kathy Sierra and Bert Bates and this book is confusing me so much. On page 245 they state that the following code below. Integer i1 = 1000; Integer i2 = 1000; if(i1 != i2) System.out.println(\"different objects\"); //Prints output different objects Then on the very next page they have the following code Integer i3 = 10; Integer i4 = 10; if(i3 == i4) System.out.println(\"same objects\"); //Prints output same objects I\'m so confused! When I try this out on my own it

Are Variable Operators Possible?

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问题 Is there a way to do something similar to either of the following: var1 = 10; var2 = 20; var operator = \"<\"; console.log(var1 operator var2); // returns true -- OR -- var1 = 10; var2 = 20; var operator = \"+\"; total = var1 operator var2; // total === 30 回答1: Not out of the box. However, it's easy to build by hand in many languages including JS. var operators = { '+': function(a, b) { return a + b }, '<': function(a, b) { return a < b }, // ... }; var op = '+'; alert(operators[op](10, 20));

Are Variable Operators Possible?

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Is there a way to do something similar to either of the following: var1 = 10; var2 = 20; var operator = "<"; console.log(var1 operator var2); // returns true -- OR -- var1 = 10; var2 = 20; var operator = "+"; total = var1 operator var2; // total === 30 Not out of the box. However, it's easy to build by hand in many languages including JS. var operators = { '+': function(a, b) { return a + b }, '<': function(a, b) { return a < b }, // ... }; var op = '+'; alert(operators[op](10, 20)); You can use ascii-based names like plus , to avoid going through strings if you don't need to. However, half of