净相当于旧VB的左侧（字符串，长度）的功能？ [英] .Net equivalent of the old vb left(string, length) function?

问题描述

作为一个非.NET程序员，我正在寻找的.NET相当于旧的VB函数左（字符串，长度）。这是懒惰的，因为它的工作任何长度的字符串。正如预期的那样，左（FOOBAR，3）=富时，最有益，左（F，3）=F 。

As a non .net programmer I'm looking for the .net equivalent of the old vb function left(string, length). It was lazy in that it worked for any length string. As expected, left("foobar", 3) = "foo" while, most helpfully, left("f", 3) = "f".

在.NET string.Substring（索引，长度）引发的一切异常超出范围。在Java中，我总是有Apache的共享lang.StringUtils得心应手。在谷歌我没有得到很远的搜索字符串函数。

In .net string.Substring(index, length) throws exceptions for everything out of range. In Java I always had the Apache-Commons lang.StringUtils handy. In Google I don't get very far searching for string functions.

编辑：

@Noldorin - 哇，谢谢你的vb.net扩展！我第一次遇到，但我花了几秒钟的时间在C＃中做同样的：

@Noldorin - Wow, thank you for your vb.net extensions! My first encounter, although it took me several seconds to do the same in c#:

public static class Utils
{
    public static string Left(this string str, int length)
    {
        return str.Substring(0, Math.Min(length, str.Length));
    }
}

请注意静态的类和方法，以及在这关键字。是的，他们是简单调用为foobar的。左（3）。另请参见 C＃扩展MSDN上。

Note the static class and method as well as the this keyword. Yes, they are as simple to invoke as "foobar".Left(3). See also c# extensions on msdn.

推荐答案

下面是会做的工作的扩展方法。

Here's an extension method that will do the job.

<System.Runtime.CompilerServices.Extension()> _
Public Function Left(ByVal str As String, ByVal length As Integer) As String
    Return str.Substring(0, Math.Min(str.Length, length))
End Function

这意味着你可以使用它就像旧VB 左功能（即左（FOOBAR，3））或使用较新的VB.NET的语法，即

This means you can use it just like the old VB Left function (i.e. Left("foobar", 3) ) or using the newer VB.NET syntax, i.e.

Dim foo = "f".Left(3) ' foo = "f"
Dim bar = "bar123".Left(3) ' bar = "bar"

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