operators

问题 This question already has answers here : Difference between a+b and a.__add__(b) (1 answer) Python: __add__ and +, different behavior with float and integer (1 answer) Closed 16 days ago . I was expecting __add__ to work, but that's obviously not the case (in Python 3.8.0 at least): >>> 10 .__add__(5.5) NotImplemented >>> 10 .__radd__(5.5) NotImplemented The other way around works: >>> 5.5 .__add__(10) 15.5 >>> 5.5 .__radd__(10) 15.5 Why doesn't the first code work? Is there a good reason

问题 I have a struct that looks something like: struct foo_t { template <std::size_t x, std::size_t y> std::size_t operator()() const { return /*something dealing with x and y*/; } }; The definition seems to compile fine, but how do I call it? I can't seem to get anything past the compiler: foo_t foo; foo<3, 3>(); // ERROR: Compiler seems to think I'm asking for "foo < 3 ..." 回答1: It's ugly, but.., foo_t foo; foo.operator()<3, 3>(); Online demo. 来源： https://stackoverflow.com/questions/11105060/how

问题 Just switched to Java from php I encountered following issue I want to rewrite if(usrname.equals(username) && (passwd.equals(password))){ return true; } else{ return false; } as (usrname.equals(username) && passwd.equals(password) )? return true : return false; it is not working(syntax error) however, int a=1; int b=2; int minVal = a < b ? a : b; is working Why ternary operator are not behaving correctly while returning value depending on some condition EDIT return (usrname.equals(username) &

问题 Just switched to Java from php I encountered following issue I want to rewrite if(usrname.equals(username) && (passwd.equals(password))){ return true; } else{ return false; } as (usrname.equals(username) && passwd.equals(password) )? return true : return false; it is not working(syntax error) however, int a=1; int b=2; int minVal = a < b ? a : b; is working Why ternary operator are not behaving correctly while returning value depending on some condition EDIT return (usrname.equals(username) &

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: Why use pointers? I know what the C++ & does. but what can it be used for? 回答1: & is used to pass address of arguments (pointer) to function, when it's used at calling site. & is used to pass arguments by reference to function, when it's used in function parameter list. & is bitwise AND . e.g. (a & b) & is used in logical AND . In this case, two & make logical AND . e.g (a && b) . 回答2: For example to pass a

问题 Can you pass in an operation like "divide by 2" or "subtract 1" using just a partially applied operator, where "add 1" looks like this: List.map ((+) 1) [1..5];; //equals [2..6] // instead of having to write: List.map (fun x-> x+1) [1..5] What's happening is 1 is being applied to (+) as it's first argument, and the list item is being applied as the second argument. For addition and multiplication, this argument ordering doesn't matter. Suppose I want to subtract 1 from every element (this

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 null coalescing translates roughly to return x, unless it is null, in which case return y I often need return null if x is null, otherwise return x.y I can use return x == null ? null : x.y; Not bad, but that null in the middle always bothers me -- it seems superfluous. I'd prefer something like return x :: x.y; , where what follows the :: is evaluated only if what precedes it is not null . I see this as almost an opposite to null coalescence, kind of mixed in with a terse, inline null-check,

问题 null coalescing translates roughly to return x, unless it is null, in which case return y I often need return null if x is null, otherwise return x.y I can use return x == null ? null : x.y; Not bad, but that null in the middle always bothers me -- it seems superfluous. I'd prefer something like return x :: x.y; , where what follows the :: is evaluated only if what precedes it is not null . I see this as almost an opposite to null coalescence, kind of mixed in with a terse, inline null-check,

问题 I am curious how to correctly use %d in the C language. I am currently taking a course in C programming and we were given a small challenge to edit a code from the textbook (C Programming A Modern Approach, K. N. KING). The goal was to edit the code from three inputs of the bar code: the 1st digit, the 5th, and the 5th to last into one single input, or all 11 digits at once. In the way the text explains the operator, I believe that %1d allows the entered integers to be individually assigned