man 真好用

最新推荐文章于 2024-10-09 22:05:08 发布

CaspianSea

最新推荐文章于 2024-10-09 22:05:08 发布

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本文链接：https://blog.youkuaiyun.com/CaspianSea/article/details/11911689

今天写一个程序，因为没有加括号，导致实际的运算优先级和认为的不一样，花了不少冤枉时间。

问题是这样的，

A & B == B

我想要的evaluation 顺序是 (A & B ) == B，而且认为 &优先级高于 ==.

实际上并非如此。所以，实际的顺序是 A & (B == B).

这个优先级可以从man 里面查到。方法是 man operator

OPERATOR(7)                                   Linux Programmer's Manual                                  OPERATOR(7)

NAME
       operator - C operator precedence and order of evaluation

DESCRIPTION
       This manual page lists C operators and their precedence in evaluation.

       Operator                             Associativity
       () [] -> .                           left to right
       ! ~ ++ -- + - (type) * & sizeof      right to left
       * / %                                left to right
       + -                                  left to right
       << >>                                left to right
       < <= > >=                            left to right
       == !=                                left to right
       &                                    left to right
       ^                                    left to right
       |                                    left to right
       &&                                   left to right
       ||                                   left to right
       ?:                                   right to left
       = += -= *= /= %= <<= >>= &= ^= |=    right to left
       ,                                    left to right

如果不知道有 operator也没关系，可以通过关键字查询：

man -k precedence
operator (7)         - C operator precedence and order of evaluation