“（f（x））+ g（y）”能否确保在C ++中首先调用f（x）？

Question

And does f(x)+(g(y)) can make sure call g(y) first? I know the order in expression is undefined in many case, but in this case does parentheses work?

Answer 1

Parentheses exist to override precedence. They have no effect on the order of evaluation.

Answer 2

Look ma, two lines!

auto r = g(y);
f(x) + r;

This introduces the all-important sequence point between the two function calls. There may be other ways to do it, but this way seems straightforward and obvious. Note that your parentheses do not introduce a sequence point, so aren't a solution.

Answer 3

No. Unless the + operator is redefined, things like that are evaluated left to right. Even if you were able to influence the precedence in the operator, it wouldn't necessarily mean that f and g were evaluated in the same order. If you need f to be evaluated before g , you can always do:

auto resultOfF = f(x);
auto resultOfG = g(x);
resultOfF + resultOfG;