[推荐]“&”和 “+” 的区别

FENGJUN

The Difference Between & and + There are times when you may need to concatenate something to a string, but only if the string actually has a value. For example, you may want to include the Middle Initial in a person’s full name. If you write code like this strFullName = FirstName & " " & MiddleInitial & " " & LastName you will have a small problem. People with no middle name(it is null in the table) will have two spaces between their first and last names, like this: Tom Smith Fortunately, there is another concatenation operator: ”+”. The technical explanation of this operator is “concatenation with null propagation.” That’s a great phrase to impress your friends with at parties, butan easier explanation is that it concatenates two strings like the ”&” operator, but only if both strings have a value. If either one is Null, the result of the whole concatenation operation is Null. +连接两个非Null字符串时的作用与&相同，但只要其中的一个字串为Null值,则连接结果就会是Null Using our FullName example, the goal is to have only onespace separating First and Last names if there is no Middle Initial. Using +, we can tack on the extra space only if the Middle Name is not null: MiddleName + " " The whole thing looks like this: strFullName = FirstName & " " & (MiddleInitial + " ") & LastName 在MiddleInitial为Null值时，(MiddleInitial + " ")中的“+”避免了用“&”时在FirstName与LastName中出现两个空格的不合理结果。 Notice that you can use parentheses () to ensure that the operations happen in the correct order. In this case, the inner phrase (MiddleInitial + " ") will evaluate to the Middle Initial plus a space, or to null (if there is no middle initial). Then, the rest of the statement will be performed.

[此贴子已经被作者于2006-1-13 15:18:44编辑过]

plxmm

谢谢分享

Long_III

谢谢分享！很少用到“+”号

chenhuafu

能翻译出来吗？感觉很有必要了解他们的异同与功能，但是E文看的很难受啊！

以下是引用[I]FENGJUN[/I]在2006-1-13 15:17:44的发言：[BR]The Difference Between & and + There are times when you may need to concatenate something to a string, but only if the string actually has a value. For example, you may want to include the Middle Initial in a person’s full name. If you write code like this strFullName = FirstName & " " & MiddleInitial & " " & LastName you will have a small problem. People with no middle name(it is null in the table) will have two spaces between their first and last names, like this: Tom Smith Fortunately, there is another concatenation operator: ”+”. The technical explanation of this operator is “concatenation with null propagation.” That’s a great phrase to impress your friends with at parties, butan easier explanation is that it concatenates two strings like the ”&” operator, but only if both strings have a value. If either one is Null, the result of the whole concatenation operation is Null. +连接两个非Null字符串时的作用与&相同，但只要其中的一个字串为Null值,则连接结果就会是Null Using our FullName example, the goal is to have only onespace separating First and Last names if there is no Middle Initial. Using +, we can tack on the extra space only if the Middle Name is not null: MiddleName + " " The whole thing looks like this: strFullName = FirstName & " " & (MiddleInitial + " ") & LastName 在MiddleInitial为Null值时，(MiddleInitial + " ")中的“+”避免了用“&”时在FirstName与LastName中出现两个空格的不合理结果。 Notice that you can use parentheses () to ensure that the operations happen in the correct order. In this case, the inner phrase (MiddleInitial + " ") will evaluate to the Middle Initial plus a space, or to null (if there is no middle initial). Then, the rest of the statement will be performed.

huyingguan

又多学了一个！谢谢

gorden_d

学海无涯，谢谢。

601476

QUOTE:

以下是引用chenhuafu在2006-2-6 11:08:45的发言：
能翻译出来吗？感觉很有必要了解他们的异同与功能，但是E文看的很难受啊！

QUOTE:

以下是引用[I]FENGJUN[/I]在2006-1-13 15:17:44的发言：[BR]The Difference Between & and +
There are times when you may need to concatenate something to a string, but only if the string actually
has a value. For example, you may want to include the Middle Initial in a person’s full name. If you
write code like this
strFullName = FirstName & " " & MiddleInitial & " " & LastName
you will have a small problem. People with no middle name(it is null in the table) will have two spaces
between their first and last names, like this:
Tom  Smith
Fortunately, there is another concatenation operator: ”+”. The technical explanation of this operator is
“concatenation with null propagation.” That’s a great phrase to impress your friends with at parties, butan easier explanation is that it concatenates two strings like the ”&” operator, but only if both strings have a value. If either one is Null, the result of the whole concatenation operation is Null.
+连接两个非Null字符串时的作用与&相同，但只要其中的一个字串为Null值,则连接结果就会是Null
Using our FullName example, the goal is to have only onespace separating First and Last names if there
is no Middle Initial. Using +, we can tack on the extra space only if the Middle Name is not null:
MiddleName + " "
The whole thing looks like this:
strFullName = FirstName & " " & (MiddleInitial + " ") & LastName
在MiddleInitial为Null值时，(MiddleInitial + " ")中的“+”避免了用“&”时在FirstName与LastName中出现两个空格的不合理结果。
Notice that you can use parentheses () to ensure that the operations happen in the correct order. In this
case, the inner phrase (MiddleInitial + " ") will evaluate to the Middle Initial plus a space, or to null (if there is no middle initial). Then, the rest of the statement will be performed.

&和+之间分别,实际上只有string事件,在于您需要连接某事件string时,

寻找一个值。 如您在人的全名中寻找字节时。 代码如下,

strFullName = FirstName & ““& MiddleInitial &” “& LastName

您会发现一个小问题。 全名中间没有中间名(它在表里是空的)如Tom Smith的空间(space)

Tom Smith

幸好有另一置符： ”+”能弥补以上不足. 这置符解释是

“concatenation with null propagation.”最能在派对打动您们的朋友， "&"的作用更加容易解释是它连接两个string ， 但，只有当两个字串的值。 如果二者之一为空的， 整体运算结果是空的。

+连接两个非Null字符串时的作用与&相同，但只要其中的一个字串为Null值,则连接结果就会是Null

使用以上例子， 最初如果没有中间，目标仅是一个空间分隔

名字和姓。 使用+符， 若中间名字不为空，我们可以另加：

MiddleName + " "

整件事例如下,

strFullName = FirstName & " " & (MiddleInitial + " ") & LastName

在MiddleInitial为Null值时，(MiddleInitial + " ")中的“+”避免了用“&”时在FirstName与LastName中出现两个空格的不合理结果。

在这个事例注意您能使用括号()按条件确保正确的运算结果。

在(MiddleInitial +  " ")内,将判断中间字符加上了空间， 或零位(如没有中间)。 然后， 其余声明将会执行。

Robinhuang

翻译的不太顺啊。

看得别扭！

向您问好

thanks

slbjw

呵呵，那我来翻译一下吧。
总的来说是这样的，用+和&的效果一样，只不过当被符号连接的变量里有一个或多个变量是空值时，&后面的变量显示一个空格，+后面的变量干脆不显示。也就是用+可以避免有空变量时产生无用的空格。
翻译完毕。

[ 本帖最后由 slbjw 于 2010-1-11 19:52 编辑 ]