operator-precedence

问题 According to the table of precedence of operators in C/C++ language (see Wikipedia), the increment operator (++) takes precedence with respect to the assignment operator (=). Can someone explain why the compiler first assign the value (1 in bill[x]) and then increases the index value (i++) in this simple program. I think it should be the opposite (first increase and then assign): #include <iostream> using namespace std; int bill[] = {16, 17, 18, 19, 20}; int main () { int i = 3; bill[(i++)] =

问题 I'm trying to figure out some default operator precedences in Haskell, but I was unable to find some good documentation on -> , = and (as in f x ). So I tried :i (->) and :i (=) in GHCI to get some info, but it gives me a syntax error. Apparently these "tokens" are just a built-in part of the syntax, so no wonder, that :i doesn't work. I'm new to Haskell, so I wasn't aware of the fact, that = doesn't return any value, I just mistakingly assumed, that it behaves as its equivalents in

问题 Since version 1.80, Cppcheck tells me that Expression 'msg[ipos++]=checksum(&msg[1],ipos-1)' depends on order of evaluation of side effects in this code sequence (simplified, data is a variable) BYTE msg[MAX_MSG_SIZE]; // msg can be smaller, depending on data encoded int ipos = 0; msg[ipos++] = MSG_START; ipos += encode(&msg[ipos], data); msg[ipos++] = checksum(&msg[1], ipos-1); // <---- Undefined Behaviour? msg[ipos++] = MSG_END; // increment ipos to the actual size of msg and treats this as

问题 Say I have an expression as follows (where ⨁ and ⨂ are binary operators which have the same precedence level but not the same associativity): x ⨁ y ⨂ z Would y belong to ⨁ or ⨂ , and based on what criteria? 回答1: According to the Edsgar Dijkstra's Shunting-yard algorithm if neighboring two operators in an expressions have the same precedence level then the expression is disambiguated based on the associativity of the second operator. If the second operator is left associative then the operand

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . A quick search for C++ precedence yields many attempts. The disconcerting part is that they are all different. Most are assuredly wrong, albeit in minor details. I will include three. The first, from cppreference.com claims there are 16 levels of precedence. Learn.cpp has 18. A simpler table at university of

问题 Background I am learning the sicp according to an online course and got confused by its lecture notes. In the lecture notes, the applicative order seems to equal cbv and normal order to cbn. Confusion But the wiki points out that, beside evaluation orders(left to right, right to left, or simultaneous), there is a difference between the applicative order and cbv: Unlike call-by-value, applicative order evaluation reduces terms within a function body as much as possible before the function is

问题 #include <iostream> int foo() { std::cout<<"foo() is called\n"; return 9; } int bar() { std::cout<<"bar() is called\n"; return 18; } int main() { std::cout<<foo()<<' '<<bar()<<' '<<'\n'; } // Above program's behaviour is unspecified // clang++ evaluates function arguments from left to right: http://melpon.org/wandbox/permlink/STnvMm1YVrrSRSsB // g++ & MSVC++ evaluates function arguments from right to left // so either foo() or bar() can be called first depending upon compiler. Output of above

问题 The C++11 standard (5.17, expr.ass) states that In all cases, the assignment is sequenced after the value computation of the right and left operands, and before the value computation of the assignment expression. With respect to an indeterminately-sequenced function call, the operation of a compound assignment is a single evaluation As I understand it, all expressions which are a part of the given assignment will be evaluated before the assignment itself. This rule should work even if I

问题 In Python3, a = b = 3 a is None == b is None returns False, but (a is None) == (b is None) returns True. So I would assume based on this example alone, == has precedence over is . However, a = b = None a is None == b is None returns True. And (a is None) == (b is None) returns True. But a is (None == b) is None returns False. In this case, it would seem as if is has precedence over ==. To give another example, and this expression isn't meant to do anything, but bear with me please. If I say

问题 In JavaScript and Java, the equals operator ( == or === ) has a higher precedence than the OR operator ( || ). Yet both languages (JS, Java) support short-circuiting in if statements: When we have if(true || anything()) , anything() isn't evaluated. You can also have the following expression: true || foo == getValue()) - for example in an output statement such as console.log(...); , or in an assignment. Now, according to operator precedence, short-circuiting shouldn't happen, as === = == > ||