为什么在C / C ++中没有^^运算符？ [英] Why is there no ^^ operator in C/C++?
问题描述
& 有&& 。 | 有 || 。为什么 ^ 有 ^^ ？
& has &&. | has ||. Why doesn't ^ have ^^?
我理解它不会是短路的，但它会有不同的语义。在C中， true 实际上是任何非零值。位异或不总是与逻辑XOR相同的：
I understand that it wouldn't be short-circuiting, but it would have different semantics. In C, true is really any non-zero value. Bitwise XOR is not always the same thing as logical XOR:
int a=strcmp(str1,str2);// evaluates to 1, which is "true"
int b=strcmp(str1,str3);// evaluates to 2, which is also "true"
int c=a ^^ b; // this would be false, since true ^ true = false
int d=a ^ b; //oops, this is true again, it is 3 (^ is bitwise)
t总是依赖于 1 或 -1 的真值，不会是 ^ ^ 操作符是非常有帮助？我经常要做这样奇怪的事情：
Since you can't always rely on a true value being 1 or -1, wouldn't a ^^ operator be very helpful? I often have to do strange things like this:
if(!!a ^ !!b) // looks strange
推荐答案
有历史和实际的原因，为什么没有
^^运算符。
实用的是：操作员没有太多的用处。 && 和 || 的要点是利用它们的短路评估，
[...]
相反， ^^ 操作符总是强制评估表达式的两个臂，因此没有效率增益。此外， ^^ 真正被调用的情况是非常罕见的，虽然可以创建示例。当你堆栈运算符时，这些情况变得稀少和陌生。
The practical is: there's not much use for the operator. The main point of && and || is to take advantage of their short-circuit evaluation not only for efficiency reasons, but more often for expressiveness and correctness.
[...]
By contrast, an ^^ operator would always force evaluation of both arms of the expression, so there's no efficiency gain. Furthermore, situations in which ^^ is really called for are pretty rare, though examples can be created. These situations get rarer and stranger as you stack up the operator--
if (cond1() ^^ cond2() ^^ cond3() ^^ ...) ...
condx（） s为真。相比之下，&& 和 || 类似物仍然相当合理和有用。
does the consequent exactly when an odd number of the condx()s are true. By contrast, the && and || analogs remain fairly plausible and useful.
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