因为任何非零都表示为真，但是 > , < , ==等运营商返回 1事实上，我很好奇是否有任何著名的 C 编译器，其中这些运算符可以产生大于 1 的值.
换句话说，有没有编译器在哪里 int i = (a==b) ;如果我打算使用 i 会导致未定义的行为不是 bool 值，而是整数，并假设它是 0或 1 ？
最佳答案
不，即使有，它们也不是 C 编译器:-) 标准要求关系运算符和相等运算符返回 1 表示真，0 表示假。
C 将整数值解释 为 bool 值的规则指出 0为假，任何其他值为真。请参阅处理 if/while/do/for 的 C11 部分，它们都包含类似 "while the expression compares unequal to zero" 的语言.具体来说:
6.8.4.1/2: In both forms [of the if statement, one with and one without an else clause], the first substatement is executed if the expression compares unequal to 0. In the else form, the second substatement is executed if the expression compares equal to 0.
6.8.5/4: An iteration statement [while, do and for] causes a statement called the loop body to be executed repeatedly until the controlling expression compares equal to 0.
但是，对于比较类型的表达式，您将得到什么结果是非常明确的，您要么得到 0或 1 .这些 C11 标准的相关位都在 6.5 Expressions 下:
6.5.8/6: Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is false.
6.5.9/3: The == (equal to) and != (not equal to) operators are analogous to the relational operators except for their lower precedence. Each of the operators yields 1 if the specified relation is true and 0 if it is false.
6.5.13/3: The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it yields 0.
6.5.14/3: The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it yields 0.
6.5.3.3/5: The result of the logical negation operator ! is 0 if the value of its operand compares unequal to 0, 1 if the value of its operand compares equal to 0.
而且这种行为方式可以追溯到 C99 和 C89(ANSI 时代)。处理关系运算符和相等运算符的 C99 部分还声明返回值为 0 或 1。
而且，虽然 C89 草案没有明确规定相等运算符的返回值，但它确实说:
The == (equal to) and the != (not equal to) operators are analogous to the relational operators except for their lower precedence.
关系运算符部分确实声明:
Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is false.
引用:http://flash-gordon.me.uk/ansi.c.txt因为我周围没有任何 C89 标准的副本。我确实有第二版 K&R(1988 年的 ANSI 版本)，在引用手册附录 A 的 A7.9 和 A7.10 节中基本上说了同样的事情。如果您想从第一版中得到明确的答案，那必须来自妻子不太愿意扔旧垃圾的人。
附录:
根据 Michael Burr 的说法，在保留旧书方面，他要么未婚，要么有一个比我更乐于助人的妻子 :-)
K&R 1st Edition (1978) also says the same in 7.6 and 7.7: "The [relational operators] all yield 0 if the specified relation is false and 1 if it is true." ... "The [equality operators] are exactly analogous to the relational operators except for their lower precedence."
关于c - "=="的计算结果大于 1 的任何 C 编译器？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10632237/