如果比较：价值第一 [英] if comparison: value first
问题描述
我在一些代码中看到，我现在不记得它是c＃还是c ++，
当他们执行比较时他们先使用该值然后再使用
变量，如：
if（null == variable）{}
有没有对此的解释或者是和往常一样
变量==价值？
-
Santi
www.syltek.com
I see in some code, I don′t remember now if it is c# or c++, that the
when they perform a comparison they use the value first and then the
variable, like:
if( null == variable ){}
Is there an explanation for this or is it the same as doing the usual
variable == value?
--
Santi
www.syltek.com
推荐答案
是否有解释或与通常的
变量==值相同？
Is there an explanation for this or is it the same as doing the usual
variable == value?
在C ++中人们使用它避免写错
如果（变量=值）
错误的话。这是完全有效的C ++代码（虽然现代编译器
生成警告），你可以在其中获得变量赋值而不是
a比较。
因为你不能在C＃中犯这个错误，所以你写的东西无关紧要。
Mattias
-
Mattias Sj？gren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
请回复到新闻组。
In C++ people use it to avoid writing
if ( variable = value )
by mistake. That''s perfectly valid C++ code (though modern compilers
generate a warning) where you get an assignment to variable instead of
a comparison.
Since you can''t make that mistake in C#, it doesn''t matter which order
you write things in.
Mattias
--
Mattias Sj?gren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.
嗨Santi，
它与做（变量==值）相同。我认为没有理由做其他事情比公司政策好。我当然发现阅读起来比常规变量==值更难，而且= / $
任何代码都很少找到值==变量。
-
快乐编码！
Morten Wennevik [C＃MVP]
Hi Santi,
It is the same as doing (variable == value). No reason for doing it other
than company policy I suppose. I certainly find it harder to read than
the regular variable == value, and value == variable is rarely found in
any code.
--
Happy Coding!
Morten Wennevik [C# MVP]
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我看到了一些代码，我现在不记得是否是c＃或c ++，当他们执行比较时，他们首先使用值然后使用
变量，如：
if（null == variable）{}
是否有解释或与通常的
变量==值相同？
I see in some code, I don′t remember now if it is c# or c++, that the
when they perform a comparison they use the value first and then the
variable, like:
if( null == variable ){}
Is there an explanation for this or is it the same as doing the usual
variable == value?
最终结果是一样的，但是有一个原因。
在C ++中，if语句对数字进行操作（0为假而非零）
是真的，大部分时间都是如此），因此有可能偶然发生
if（variable = 5）
{
}
并将if语句始终评估为true。执行5 =变量
会导致编译器抱怨您无法分配值，因此
捕获该错误并避免错误。
它在C＃中不太重要，因为你只能用boolean
类型本身导致这个错误。
The end result is the same, however there is a reason.
In C++, if statements operated on numbers(0 being false and not-zero being
true, most of the time), therefore it was possible to accidentally do
if (variable = 5)
{
}
and have that if statement to always evaluate to true. Doing 5 = variable
causes the compiler to complain that you cannot assign to a value, thus
catching that error and avoiding a bug.
Its less important in C#, as you can only cause this error with boolean
types themselves.
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