首先在"if"语句中添加常量的背后原因是什么? [英] What's the reasoning behind putting constants in 'if' statements first?

问题描述

我正在查看一些我正在使用的硬件接口的示例C ++代码，并注意到以下几行语句:

I was looking at some example C++ code for a hardware interface I'm working with and noticed a lot of statements along the following lines:

if ( NULL == pMsg ) return rv;

我敢肯定我听过人们说把常量放在第一位是一个好主意，但是为什么呢?仅仅是这样，如果您有一个大的陈述，就可以快速看到要与之比较的内容，或者还有更多内容?

I'm sure I've heard people say that putting the constant first is a good idea, but why is that? Is it just so that if you have a large statement you can quickly see what you're comparing against or is there more to it?

推荐答案

这样就不会将比较(==)与分配(=)混用.

So that you don't mix comparison (==) with assignment (=).

如您所知，您不能分配给常量.如果尝试这样做，编译器会给您一个错误.

As you know, you can't assign to a constant. If you try, the compiler will give you an error.

基本上，它是防御性编程技术之一.为了保护自己免受伤害.

Basically, it's one of defensive programming techniques. To protect yourself from yourself.

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