执行顺序为，如果有多个条件语句 [英] Order of execution for an if with multiple conditionals

问题描述

在具有多个条件语句if语句，是如果第一结果是明确的执行的第二条件

In an if statement with multiple conditionals, is the second conditional executed if the outcome of the first is clear?

例如：

if(i>0 && array[i]==0){
}

如果我换了我的负值可能会出现段错误的条件语句，但这种方式没有发生段错误。我可以肯定地说这始终工作或确实有需要使用嵌套的if语句？

If I swap the conditionals a segfault may occur for negative values of i, but this way no segfault occurs. Can I be sure that this always works or do have have to use nested if statements?

推荐答案

这类型的评价被称为短路。
一旦结果是100％的清楚，它不会继续评估。

This type of evaluation is called short-circuiting. Once the result is 100% clear, it does not continue evaluating.

这实际上是一个常见的​​编程技术。
例如，在C ++中，你经常会看到类似这样的：

This is actually a common programming technique. For example, in C++ you will often see something like:

if (pX!=null && pX->predicate()) { bla bla bla }

如果您更改条件的顺序，你可以调用一个空指针的方法和崩溃。当你有一个指向该结构在C A类似的例子将使用结构的领域。

If you changed the order of the conditions, you could be invoking a method on a null pointer and crashing. A similar example in C would use the field of a struct when you have a pointer to that struct.

您可以做类似的东西带或：

You could do something similar with or:

if(px==null || pX->isEmpty()} { bla bla bla }

这也是原因之一，这通常是一个好主意，以避免在if条件的副作用。

This is also one of the reasons that it is generally a good idea to avoid side effects in an if condition.

例如，假设你有：

if(x==4 && (++y>7) && z==9)

如果x为4，那么y将无论递增Z或y的值的，但是，如果它不是4，它不会在所有递增

If x is 4, then y will be incremented regardless of the value of z or y, but if it is not 4, it will not be incremented at all.

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