short-circuiting

问题 Say I have this code: unsigned int func1(); unsigned int func2(); unsigned int func3(); unsigned int x = func1() | func2() | func3(); Does C++ guarantee that func1() will be called first, then func2(), and then func3()? Or is the compiler allowed to call the functions in any order it feels like? Also, is the compiler allowed to implement a short-circuit optimization here if it wants to? (e.g. if func1() returned ~0, could the compiler decide not to bother calling func2() or func3(), because

问题 I'm new to Haskell, and I'm trying a bit: isPrime :: Integer->Bool isPrime x = ([] == [y | y<-[2..floor (sqrt x)], mod x y == 0]) I have a few questions. Why when I try to load the .hs, WinHugs say: Instances of (Floating Integer, RealFrac Integer) required for definition of isPrime ? When the interpreter finds one element in the right set, it immediately stops or it computes all the set? I think you know what I mean. Sorry about my english. 回答1: 1) The problem is that sqrt has the type

问题 In the code below: #include <stdio.h> int main() { int a = 1; int b = 1; int c = a || --b; int d = a-- && --b; printf("a = %d, b = %d, c = %d, d = %d", a, b, c, d); return 0; } i was expecting the output to be: a=0,b=1,c=1,d=0 because due to short circuiting in the line below, ie a-- returns 0 so the other part wont get executed right? int d = a-- && --b; The output is: a = 0, b = 0, c = 1, d = 0 can anyone please explain? 回答1: int c = a || --b; In this line, the C standard requires the C

问题 Do we have any operator in C# by which I can avoid short circuit evaluation and traverse to all the conditions. say if(txtName.Text.xyz() || txtLastName.Text.xyz()) { } public static bool xyz(this TextBox txt) { //do some work. return false; } It should evaluate all conditions irrespective of output obtained. And after evaluating last condition continues according to result obtained. ? 回答1: Just use a single bar, this will evaluated both arguments regardless of the outcome of the first result

问题 While performing a check if there's a camera present and enabled on my windows mobile unit I encountered something I don't understand. The code looks like this: public static bool CameraP(){ return Microsoft.WindowsMobile.Status.SystemState.CameraPresent; } public static bool CameraE() { return Microsoft.WindowsMobile.Status.SystemState.CameraEnabled; } public static bool CameraPresent1() { return Microsoft.WindowsMobile.Status.SystemState.CameraPresent && Microsoft.WindowsMobile.Status

问题 This question already has answers here : Is the shortcircuit behaviour of Python's any/all explicit? (4 answers) Closed 2 years ago . I wish to use the Python all() function to help me compute something, but this something could take substantially longer if the all() does not evaluate as soon as it hits a False . I'm thinking it probably is short-circuit evaluated, but I just wanted to make sure. Also, is there a way to tell in Python how the function gets evaluated? 回答1: Yes, it short

问题 I tried something along the lines of: if(myString != nil && myString.length) { ... } And got: -[NSNull length]: unrecognized selector sent to instance Does Objective-C not short-circuit after the first condition fails? 回答1: Objective-C does support short-circuit evaluation, just like C. It seems that in your example myString is NSNull and not nil , therefore myString != nil is true. NSNull is a singleton and is used to represent nil where only objects are allowed, for example in an NSArray.

问题 Assume myObj is null. Is it safe to write this? if(myObj != null && myObj.SomeString != null) I know some languages won't execute the second expression because the && evaluates to false before the second part is executed. 回答1: Yes. In C# && and || are short-circuiting and thus evaluates the right side only if the left side doesn't already determine the result. The operators & and | on the other hand don't short-circuit and always evaluate both sides. The spec says: The && and || operators are

问题 So for binary operators on booleans, Java has & , | , ^ , && and || . Let's summarize what they do briefly here: JLS 15.22.2 Boolean Logical Operators &, ^, and | JLS 15.23 Conditional-And Operator && JLS 15.24 Conditional-Or Operator || For & , the result value is true if both operand values are true ; otherwise, the result is false . For | , the result value is false if both operand values are false ; otherwise, the result is true . For ^ , the result value is true if the operand values are

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Does java evaluate remaining conditions after boolean result is known Why do we usually use || not |, what is the difference? I missed my class lecture the other day and I was wondering if anyone could give an explanation what short circuiting is and maybe an example of it being used in a simple Java program. Thanks for your help! 回答1: Short-circuiting is where an expression is stopped being evaluated as soon as