equality-operator

问题 According to cppreference, std::type_info::operator!= gets removed with C++20, however, std::type_info::operator== apparently remains. What's the reasoning behind? I might agree on comparing for inequality being meaningless, but then comparing for equality would be just as meaningless as well, wouldn't it? Similarly, operator!= of many other standard library types, including containers such as std::unordered_map::operator!= and std::unordered_set::operator!= will be removed in C++20 according

问题 According to cppreference, std::type_info::operator!= gets removed with C++20, however, std::type_info::operator== apparently remains. What's the reasoning behind? I might agree on comparing for inequality being meaningless, but then comparing for equality would be just as meaningless as well, wouldn't it? Similarly, operator!= of many other standard library types, including containers such as std::unordered_map::operator!= and std::unordered_set::operator!= will be removed in C++20 according

问题 According to cppreference, std::type_info::operator!= gets removed with C++20, however, std::type_info::operator== apparently remains. What's the reasoning behind? I might agree on comparing for inequality being meaningless, but then comparing for equality would be just as meaningless as well, wouldn't it? Similarly, operator!= of many other standard library types, including containers such as std::unordered_map::operator!= and std::unordered_set::operator!= will be removed in C++20 according

问题 I am developing an application in Android using Eclipse. I wrote the following code and in tests the first and third " if " block is not reachable. Why? When I add a leading zero to a number, the equal operator returns false. int var = 123; if (var == 0123) { //not reachable } if (var == 123) { //reachable } if (var == (int)0123) { //not reachable } if (var == (int)123) { //reachable } 回答1: 0123 is an octal number (leading 0), while 123 is a decimal number. so 0123 actually equals to 83. 回答2:

问题 Why does {} == false evaluate to false while [] == false evaluates to true in javascript? 回答1: This is the type conversion that takes place according to the Abstract Equality Comparison Algorithm: {} == false // step 7 {} == ToNumber(false) {} == 0 // step 9 ToPrimitve({}) == 0 "[object Object]" == 0 // step 5 ToNumber("[object Object]") == 0 NaN == 0 // step 1.c.i [] == false // step 7 [] == ToNumber(false) [] == 0 // step 9 ToPrimitve([]) == 0 "" == 0 // step 5 ToNumber("") == 0 0 == 0 //

问题 Why is === faster than == in PHP? 回答1: Because the equality operator == coerces, or converts, the data type temporarily to see if it’s equal to the other operand, whereas === (the identity operator) doesn’t need to do any converting whatsoever and thus less work is done, which makes it faster. 回答2: === does not perform typecasting, so 0 == '0' evaluates to true , but 0 === '0' - to false . 回答3: First, === checks to see if the two arguments are the same type - so the number 1 and the string '1

问题 A few weeks ago, I have read this thread Is < faster than <=? about comparison operators in C . It was said that there is no difference in the performance between < and <= as they are interpreted as same/similar machine commands. At the same time, in our company's "best practices", it was said that we should always use "===" to compare things instead of "==". So, I started to wonder if this is always appropriate as I am used to using the "==" and "typeof ... == " and do not want to change my

问题 Let's say I have a variable that will always be a string. Now take the code below: if($myVar === "teststring") Note: $myVar will always be a string, so my questions is Which is quicker/best, using === (indentity) or the == (equality)? 回答1: Testing for identity is always faster, because PHP does not have to Type Juggle to evaluate the comparison. However, I'd say the speed difference is in the realms of nanoseconds and totally neglectable. Related reading: PHP type comparison tables Type

问题 I want to know the difference between these: my $a = 1; and my $a == 1; and my $a eq 1; 回答1: == is used when comparing numeric values. eq is used in comparing string values. = is the assignment operator, not a comparison operator. 回答2: eq is for testing string equality, == is the same thing but for numerical equality. For More Click Here 回答3: The last two statements do nothing, it's a good practice to use the directives: use warnings; use strict; for example: #!/usr/bin/perl use warnings; use

问题 I'm working on a lecture about hard to understand JavaScript code and of course on of the weak point of JavaScript is knowing what == / === will return. I found this great answer in stack that covers this subject nicely - Which equals operator (== vs ===) should be used in JavaScript comparisons? one of the things that caught my eyes (probably because I wasn't aware of it until now) was that you can use String Objects instead of primitives and you will get different result in your conditions