short-circuiting | 易学教程

Is short-circuiting logical operators mandated? And evaluation order?

阅读更多关于 Is short-circuiting logical operators mandated? And evaluation order?

问题 Does the ANSI standard mandate the logical operators to be short-circuited, in either C or C++? I\'m confused for I recall the K&R book saying your code shouldn\'t depend on these operations being short circuited, for they may not. Could someone please point out where in the standard it\'s said logic ops are always short-circuited? I\'m mostly interested on C++, an answer also for C would be great. I also remember reading (can\'t remember where) that evaluation order isn\'t strictly defined,

Is the SQL WHERE clause short-circuit evaluated?

阅读更多关于 Is the SQL WHERE clause short-circuit evaluated?

问题 Are boolean expressions in SQL WHERE clauses short-circuit evaluated ? For example: SELECT * FROM Table t WHERE @key IS NULL OR (@key IS NOT NULL AND @key = t.Key) If @key IS NULL evaluates to true, is @key IS NOT NULL AND @key = t.Key evaluated? If No, why not? If Yes, is it guaranteed? Is it part of ANSI SQL or is it database specific? If database specific, SqlServer? Oracle? MySQL? 回答1: ANSI SQL Draft 2003 5WD-01-Framework-2003-09.pdf 6.3.3.3 Rule evaluation order [...] Where the

What is the difference between And and AndAlso in VB.NET?

阅读更多关于 What is the difference between And and AndAlso in VB.NET?

In VB.NET, what is the difference between And and AndAlso ? Which should I use? Nico The And operator evaluates both sides, where AndAlso evaluates the right side if and only if the left side is true. An example: If mystring IsNot Nothing And mystring.Contains("Foo") Then ' bla bla End If The above throws an exception if mystring = Nothing If mystring IsNot Nothing AndAlso mystring.Contains("Foo") Then ' bla bla End If This one does not throw an exception. So if you come from the C# world, you should use AndAlso like you would use && . More info here: http://www.panopticoncentral.net/2003/08