conditional-operator

问题 So I ran into something interesting that I didn't realize about the ternary operator (at least in Visual C++ 98-2010). As pointed out in http://msdn.microsoft.com/en-us/library/e4213hs1(VS.71).aspx if both the expression and conditional-expression are l-values the result is an l-value. Of course normally in c/c++ you'd write something like: int value = (x == 1) ? 1 : 0; and never even care about the r-value/l-value involvment, and in this case neither 1 nor 0 are convertible to l-values.

问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: Python “is” operator behaves unexpectedly with integers Ran into something odd last night where doing if max_urls is 0: max_urls = 10 would always return false... even when max_urls was 0.... it was getting assigned from the database. When I did a print type(max_urls) would return <type 'long'> 0 which seemed right but it would always return false. If I changed it to if max_urls == 0: max_urls = 10 then finally

问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: Python “is” operator behaves unexpectedly with integers Ran into something odd last night where doing if max_urls is 0: max_urls = 10 would always return false... even when max_urls was 0.... it was getting assigned from the database. When I did a print type(max_urls) would return <type 'long'> 0 which seemed right but it would always return false. If I changed it to if max_urls == 0: max_urls = 10 then finally

问题 I'm maintaining some code and have found the following pattern a lot: var isMale = (row["Gender"].ToString() == "M") ? true : false; instead of this: var isMale = (row["Gender"].ToString() == "M"); Is there any reason why anyone would do this? Does anyone think the former is more readable or clearer? Is there some sort of old C "gotcha" that this is a hold-over from? 回答1: A valid reason? No. It's usually produced by people who don't really understand that a condition is also in itself an

问题 This is a retelling of my previous post, since I changed the question (so it probably didn't get flagged as a new question and was missed). I'll hopefully trim it down too. I had functions like: #include <cstddef> #include <type_traits> template < typename E, typename T > inline constexpr auto checked_slice( E &&, T &&t ) noexcept -> T && { return static_cast<T &&>(t); } template < typename E, typename T, std::size_t N, typename U, typename ...V > inline constexpr auto checked_slice( E &&e, T

问题 This question already has answers here : What does '?' do in C++? (7 answers) Closed 6 years ago . This may be a bonehead question, but I cannot figure out what the ? exp : other_exp sequence is called. Example: int result = (true) ? 1 : 0; I've tried using the Google machine, but it's hard to Googilize for something without knowing what it's called. Thanks! 回答1: It is called the the conditional operator or alternativly the ternary operator as it a ternary operator (an operator which takes 3

问题 I saw this question but it uses the ?? operator as a null check, I want to use it as a bool true/false test. I have this code in Python: if self.trait == self.spouse.trait: trait = self.trait else: trait = defualtTrait In C# I could write this as: trait = this.trait == this.spouse.trait ? this.trait : defualtTrait; Is there a similar way to do this in Python? 回答1: Yes, you can write: trait = self.trait if self.trait == self.spouse.trait else defaultTrait This is called a Conditional

问题 This question already has answers here : What is the Java ?: operator called and what does it do? (16 answers) Closed 6 years ago . I dont know what the question mark ( ? ) stand for in java, I was doing a small program, a Nim-game. were looking in a book, for help and saw this statement: int pinsToTake = (min >= 2) ? 2 : 1; I don't understand it, what will ? represent, can it be something to do with if-statement but you put it in a variable? and the : can be something "else"? (this things

问题 This question already has answers here : Cannot implicitly convert type 'int' to 'short' [duplicate] (9 answers) Closed 5 years ago . Following expression is ok short d = ("obj" == "obj" ) ? 1 : 2; But when you use it like below, syntax error occurs short d = (DateTime.Now == DateTime.Now) ? 1 : 2; Cannot implicitly convert type 'int' to 'short'. An explicit conversion exists (are you missing a cast?) Can anyone explain why this is so? Is there a difference between comparing string-to-string

问题 I have an unexpected issue when using a conditional operator in java. The code is supposed to check if the ArrayList contains a specific string, then it returns true or false. It is not the first time I do this, but for some reason there's something wrong. This is my code so far: public boolean isDone() { ArrayList<String> al = new ArrayList<String>(); //Defining ArrayList al.add(d1.getText()); // Adding the text from JLabels. al.add(d2.getText()); al.add(d3.getText()); al.add(d4.getText());