AND / OR（安培;&安培; / ||）逻辑多个条件语句 [英] AND/OR (&&/||) logic for multiple condition statements

问题描述

如果你有在C＃中的if语句来检查多个条件：

If you have an if-statement in C# that checks multiple conditions:

if (a == 5 && b == 9) { ... }

确实乙== 9 仍然可以检查是否 == 5 的条件是假的，或者可以自动进行退出，因为没有办法，这可能传递了？

Does b == 9 still get checked if a == 5 condition is false, or does it automatically exit since there's no way this could pass anymore?

同样，对于一个OR if语句：

Similarly, for an OR if-statement:

if (a == 5 || b == 9) { ... }

威尔的乙== 9 仍然可以检查是否 == 5 是真的

Will b == 9 still get checked if a == 5 is true?

推荐答案

两个&放大器;？&安培; 和 || 是短路的运营商，这意味着，如果答案是从左边的操作数已知的，正确的操作数不计算。

Both && and || is "short-circuiting" operators, which means that if the answer is known from the left operand, the right operand is not evaluated.

这意味着：

a && b

B 不会，如果<评估。code> A 是假的，因为最后的答案是已知

b will not be evaluated if a is false, since the final answer is already known.

同样的：

a || b

B 不会，如果<评估code> A 是真实的，因为最后的答案是已知的。

b will not be evaluated if a is true, since the final answer is already known.

如果您的希望的两个操作数进行评估，使用&放大器; 和 | 运营商，而不是

If you want both operands to be evaluated, use the & and | operators instead.

这样做的好处是，你可以写，如果所有的操作数进行评估，将失败的表现​​。下面是一个典型的if语句：！

The bonus of this is that you can write expressions that would fail if all operands was evaluated. Here's a typical if-statement:

if (a != null && a.SomeProperty != null && a.SomeProperty.Inner != null)
    ... use a.SomeProperty.Inner

如果一个为null，表达式会继续评估 a.SomeProperty ，它会抛出一个的NullReferenceException ，但由于&放大器;&安培; 短路，如果 A 是空，表达不会评价休息，因此不会抛出异常。

If a was null, and the expression would go on to evaluate a.SomeProperty, it would throw a NullReferenceException, but since && short-circuits, if a is null, the expression will not evaluate the rest and thus not throw the exception.

显然，如果你替换&放大器;&安培; 与&安培; ，它会抛出该异常如果 A 或 a.SomeProperty 是空。

Obviously, if you replace && with &, it will throw that exception if either a or a.SomeProperty is null.

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