operator-precedence

问题 So, the C++ standard requires that class members be initialized in the order in which they are declared in the class, rather than the order that they're mentioned in any constructor's initializer list. However, this doesn't imply anything about the order in which the arguments to those initializations are evaluated. I'm working with a system that frequently passes references to serialization objects around, and wondering if I can ensure that bits are read from it in the right order,

问题 I have a question about operator precedence and associativity in Bison. In every example I see the productions are like expr 'op' expr , for example :http://dinosaur.compilertools.net/bison/bison_8.html But if I would use bison %left and others associativity tools, and I would use grammar like: expr| expr binop expr | expr relop expr | expr logical_op expr and binop: '+' | '-' | '*' | '/' ; relop: EE | NE | LE | '<' | GE | '>' ; logical_op: AND | OR ; would associativity and precedence rules

问题 This question already has answers here : Why does “++x || ++y && ++z” calculate “++x” first, even though operator “&&” has higher precedence than “||” (11 answers) Closed last year . The O/p comes out to be x=2,y=1,z=1 which doesnt agree with the operator precedence. I was running this on Turbo c++ compiler: void main() { int x,y,z,q; x=y=z=1; q=++x || ++y && ++z; printf("x=%d y=%d z=%d",x,y,z); } 回答1: Operator precedence does not in any way determine the order in which the operators are

问题 I was wondering about the order that a foreach loop in C# loops through a System.Collections.Generic.List<T> object. I found another question about the same topic, but I do not feel that it answers my question to my satisfaction. Someone states that no order is defined. But as someone else states, the order it traverses an array is fixed (from 0 to Length-1). 8.8.4 The foreach statement It was also said that the same holds for any standard classes with an order (e.g. List<T> ). I can not find

问题 In this pgexercises about joining 3 different tables, the answer is given as following: select mems.firstname || ' ' || mems.surname as member, facs.name as facility, case when mems.memid = 0 then bks.slots*facs.guestcost else bks.slots*facs.membercost end as cost from cd.members mems inner join cd.bookings bks on mems.memid = bks.memid inner join cd.facilities facs on bks.facid = facs.facid where bks.starttime >= '2012-09-14' and bks.starttime < '2012-09-15' and ( (mems.memid = 0 and bks

问题 If I try this: $a = 0; echo $a + ++$a, PHP_EOL; echo $a; I get this output: 2 1 Demo: http://codepad.org/ncVuJtJu Why is that? I expect to get this as an output: 1 1 My understanding: $a = 0; // a === 0 echo $a + ++$a, PHP_EOL; // (0) + (0+1) === 1 echo $a; // a === 1 But why isn't that the output? 回答1: All the answers explaining why you get 2 and not 1 are actually wrong. According to the PHP documentation, mixing + and ++ in this manner is undefined behavior, so you could get either 1 or 2.

问题 Is order of execution in constructor initialization list determinable? I know that members order in a class is the order in which those members will be initialized but if I have scenario like this: class X() { X_Implementation* impl_; }; and then providing that allocator is available: X::X():impl_(Allocate(sizeof(X_Implementation)))//HERE I'M ALLOCATING <--1 ,impl_(Construct<X_Implementation>(impl_))//AND HERE I'M CONSTRUCTING <--2 { } but in order for this to be dependable this order MUST be

问题 If I want to select a subset of data in R, I can use the subset function. I wanted to base an analysis on data that that was matching one of a few criteria, e.g. that a certain variable was either 1, 2 or 3. I tried myNewDataFrame <- subset(bigfive, subset = (bigfive$bf11==(1||2||3))) It did always just select values that matched the first of the criteria, here 1. My assumption was that it would start with 1 and if it does evaluate to "false" it would go on to 2 and than to 3, and if none

问题 In Bjarne Stroustrup's The C++ Programming Language 4th edition section 36.3.6 STL-like Operations the following code is used as an example of chaining: void f2() { std::string s = "but I have heard it works even if you don't believe in it" ; s.replace(0, 4, "" ).replace( s.find( "even" ), 4, "only" ) .replace( s.find( " don't" ), 6, "" ); assert( s == "I have heard it works only if you believe in it" ) ; } The assert fails in gcc ( see it live ) and Visual Studio ( see it live ), but it does

问题 What is the predefined order in which the clauses are executed in MySQL? Is some of it decided at run time, and is this order correct? FROM clause WHERE clause GROUP BY clause HAVING clause SELECT clause ORDER BY clause 回答1: The actual execution of MySQL statements is a bit tricky. However, the standard does specify the order of interpretation of elements in the query. This is basically in the order that you specify, although I think HAVING and GROUP BY could come after SELECT : FROM clause