用C逻辑运算符precedence [英] Precedence of Logical Operators in C

问题描述

可能重复：结果
  <一href=\"http://stackoverflow.com/questions/3700352/why-x-y-z-calculate-x-firstly-however-operator-is-higher\">why ＆ldquo; ++点¯x|| ++ Y'放大器;＆安培; ++ž＆rdquo;的计算＆ldquo; + X'rdquo;的首先 ？然而，运营商及ldquo;＆放大器;＆安培;＆rdquo;的比＆ldquo更高; ||＆rdquo;的

如果你看看C'S precedence表，你会看到和放大器;＆安培;具有较高的precedence比||。

If you look at C's precedence table, you'll see that && has higher precedence than ||.

不过看看下面的code：

But take a look at the following code:

a=b=c=1;

++a || ++b && ++c;

printf("%d %d %d\n",a,b,c);

据打印出2 1 1，这意味着++一个先评估，一旦程序看到一个真正有它就停在那里，因为什么是对的另一边||并不重要。

It prints out "2 1 1", meaning that the "++a" is evaluated first, and once the program sees a TRUE there it stops right there, because what is on the other side of the || is not important.

但是，由于＆功放;＆安培;具有较高的precedence比||，不应该++ B和;＆功放; + C先评估，然后将结果插回++一个||结果？ （在这种情况下，程序将打印1 2 2）。

But since && has higher precedence than ||, shouldn't "++b && ++c" be evaluated first, and then the result plugged back into "++a || result" ? (in this case the program would print "1 2 2").

推荐答案

刚刚尝试用括号想象它：

Just try to imagine it with parentheses:

++a || ++b && ++c;

等于

(++a) || (++b && ++c);

这是从左至右评价

which is evaluated from left to right.

如果＆功放;＆安培;和||将具有相同的precedence，它看起来像

if && and || would have the same precedence, it would look like

(++a || ++b) && (++c);

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