<分区>
我最近纠正了一个 C 程序中的错误:
if (foobar != FOO | BAR | BAZ)
正确的代码是
if (foobar != (FOO | BAR | BAZ))
根据C operator precedence显然 != 优先于 |。
我的问题是为什么是这样而不是相反？根据我的经验，我会经常使用 a == b || a == c 或 d == (a | b | c)，但绝不是 a == b | c == d。
这个选择背后的逻辑是什么？
最佳答案
这是有历史原因的，引用 Dennis Ritchie 的话:
“Early C had no separate operators for & and && or | and ||. Instead it used the notion (inherited from B and BCPL) of ‘truth-value context': where a Boolean value was expected, after ‘if‘ and ‘while‘ and so forth; the & and | operators were interpreted as && and || are now; in ordinary expressions, the bit-wise interpretations were used. It worked out pretty well, but was hard to explain. (There was the notion of ‘top-level operators’ in a truth-value context.) “The precedence of & and | were as they are now.
Primarily at the urging of Alan Snyder, the && and || operators were added. This successfully separated the concepts of bit-wise operations and short-circuit Boolean evaluation. However, I had cold feet about the precedence problems. For example, there were lots of programs with things like: if (a==b & c==d) …
“In retrospect it would have been better to go ahead and change the precedence of & to higher than ==, but it seemed safer just to split & and && without moving & past an existing operator.”
关于c - C 中的运算符优先级(!= 和 |)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37682090/