为什么如果（恒定的==变量）是pferred，而不是如$ P $（可变==常数） [英] Why if( constant == variable ) is preferred instead of if ( variable == constant )
问题描述
可能重复：结果
如何检查等号？ （0 == i）或（ⅰ== 0）的结果
<一href=\"http://stackoverflow.com/questions/271561/why-does-one-often-see-null-variable-instead-of-variable-null-in-c\">Why做一件经常看到＆ldquo;！=空可变的rdquo;的而不是＆ldquo;！变量=空＆rdquo;的在C＃中？结果
<一href=\"http://stackoverflow.com/questions/3309089/why-do-some-experienced-programmers-write-ex$p$pssions-this-way\">Why做一些有经验的程序员编写的前pressions这样？结果
NULL是什么意思！=在C ++中的价值？
Possible Duplicate:
How to check for equals? (0 == i) or (i == 0)
Why does one often see “null != variable” instead of “variable != null” in C#?
Why do some experienced programmers write expressions this way?
What is the meaning of NULL != value in C++?
例如，
int k =5;
if( 5 == k )
{
}
是preferred过
is preferred over
if (k == 5)
{
}
时只考虑格式化的目的还是有它背后的原因吗？
Is it considered only for formatting purpose or is there any reason behind it?
推荐答案
由于这种形式使得它更难被遗忘的等号一一介绍的错误。试想一下，如果你这样做：
Because that form makes it harder to introduce a bug by forgetting one of the equals signs. Imagine if you did this:
if (k = 5)
这是打算作为比较，但它现在是一个任务！更糟的是，它的法律的，它会弄乱你的多种方式的程序（的 K 被改变，和条件始终评估值到真正）。
This was intended as a comparison, but it's now an assignment! What's worse, it is legal, and it will mess up your program in multiple ways (the value of k is changed, and the conditional always evaluates to true).
与
if (5 = k)
这是不合法的（你不能分配到一个文本），所以编译器会立即将其标记为错误。
This is not legal (you cannot assign to a literal) so the compiler will immediately flag it as an error.
这是说，写作code的这种风格（条件语句内分配）并不像prevalent今天因为它曾经是。大多数现代编译器会将此作为一个警告，所以它不可能不被发现。我个人不喜欢第二形式，因为编译器有帮助，我不使用它。
That said, this style of writing code (assignments within conditionals) is not as prevalent today as it once was. Most modern compilers will flag this as a warning, so it's unlikely to go undetected. Personally I don't like the second form and since the compiler is there to help I don't use it.
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