如何在 VB.NET 中声明一个固定长度的字符串？
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How to declare a fixed-length string in VB.NET?
提问by Rachel
How do i Declare a string like this:
我如何声明这样的字符串：
Dim strBuff As String * 256
in VB.NET?
在 VB.NET 中？
回答by Spencer Ruport
回答by xpda
It depends on what you intend to use the string for. If you are using it for file input and output, you might want to use a byte array to avoid encoding problems. In vb.net, A 256-character string may be more than 256 bytes.
这取决于您打算将字符串用于什么目的。如果将其用于文件输入和输出，则可能需要使用字节数组来避免编码问题。在 vb.net 中，一个 256 个字符的字符串可能超过 256 个字节。
Dim strBuff(256) as byte
You can use encoding to transfer from bytes to a string
您可以使用编码从字节传输到字符串
Dim s As String
Dim b(256) As Byte
Dim enc As New System.Text.UTF8Encoding
...
s = enc.GetString(b)
You can assign 256 single-byte characters to a string if you need to use it to receive data, but the parameter passing may be different in vb.net than vb6.
如果你需要用它来接收数据，你可以为一个字符串分配 256 个单字节字符，但在 vb.net 中传递的参数可能与 vb6 不同。
s = New String(" ", 256)
Also, you can use vbFixedString. I'm not sure exactly what this does, however, because when you assign a string of different length to a variable declared this way, it becomes the new length.
此外，您可以使用 vbFixedString。但是，我不确定这到底是做什么的，因为当您将不同长度的字符串分配给以这种方式声明的变量时，它会成为新的长度。
<VBFixedString(6)> Public s As String
s = "1234567890" ' len(s) is now 10
回答by Dr.Optix
To write this VB 6 code:
要编写此 VB 6 代码：
Dim strBuff As String * 256
In VB.Net you can use something like:
在 VB.Net 中，您可以使用以下内容：
Dim strBuff(256) As Char
回答by Prince Waleed
Use stringbuilder
使用字符串生成器
'Declaration
Dim S As New System.Text.StringBuilder(256, 256)
'Adding text
S.append("abc")
'Reading text
S.tostring
回答by Gawie
Try this:
尝试这个：
Dim strbuf As New String("A", 80)
Creates a 80 character string filled with "AAA...."'s
创建一个 80 个字符的字符串，其中包含“AAA....”
Here I read a 80 character string from a binary file:
在这里，我从二进制文件中读取了 80 个字符的字符串：
FileGet(1,strbuf)
reads 80 characters into strbuf...
将 80 个字符读入 strbuf ...
回答by Mark Hurd
You can use Microsoft.VisualBasic.Compatibility:
您可以使用Microsoft.VisualBasic.Compatibility：
Imports Microsoft.VisualBasic.Compatibility
Dim strBuff As New VB6.FixedLengthString(256)
But it's marked as obsolete and specifically not supported for 64-bit processes, so write your own that replicates the functionality, which is to truncate on setting long values and padding right with spaces for short values. It also sets an "uninitialised" value, like above, to nulls.
但是它被标记为过时，并且特别不支持 64 位进程，因此编写自己的复制功能的方法，即在设置长值时截断并用空格填充短值。它还像上面一样将“未初始化”值设置为空值。
Sample code from LinqPad (which I can't get to allow Imports Microsoft.VisualBasic.CompatibilityI think because it is marked obsolete, but I have no proof of that):
来自 LinqPad 的示例代码（Imports Microsoft.VisualBasic.Compatibility我认为这是不允许的，因为它被标记为过时，但我没有证据证明）：
Imports Microsoft.VisualBasic.Compatibility
Dim U As New VB6.FixedLengthString(5)
Dim S As New VB6.FixedLengthString(5, "Test")
Dim L As New VB6.FixedLengthString(5, "Testing")
Dim p0 As Func(Of String, String) = Function(st) """" & st.Replace(ChrW(0), "Public Structure FixedLengthString
Dim mValue As String
Dim mSize As Short
Public Sub New(Size As Integer)
mSize = Size
mValue = New String(" ", mSize)
End Sub
Public Property Value As String
Get
Value = mValue
End Get
Set(value As String)
If value.Length < mSize Then
mValue = value & New String(" ", mSize - value.Length)
Else
mValue = value.Substring(0, mSize)
End If
End Set
End Property
End Structure
") & """"
p0(U.Value).Dump()
p0(S.Value).Dump()
p0(L.Value).Dump()
U.Value = "Test"
p0(U.Value).Dump()
U.Value = "Testing"
p0(U.Value).Dump()
which has this output:
有这个输出：
"\0\0\0\0\0"
"Test "
"Testi"
"Test "
"Testi"
"\0\0\0\0\0"
"测试"
"测试"
"测试"
"测试"
回答by Kanad Mehta
This object can be defined as a structure with one constructor and two properties.
该对象可以定义为具有一个构造函数和两个属性的结构。
Dim a as string
a = ...
If a.length > theLength then
a = Mid(a, 1, theLength)
End If
https://jdiazo.wordpress.com/2012/01/12/getting-rid-of-vb6-compatibility-references/
https://jdiazo.wordpress.com/2012/01/12/getting-rid-of-vb6-compatibility-references/
回答by ByongSub
''' <summary>
''' Represents a <see cref="String" /> with a minimum
''' and maximum length.
''' </summary>
Public Class BoundedString
Private mstrValue As String
''' <summary>
''' The contents of this <see cref="BoundedString" />
''' </summary>
Public Property Value() As String
Get
Return mstrValue
End Get
Set(value As String)
If value.Length < MinLength Then
Throw New ArgumentException(String.Format("Provided string {0} of length {1} contains less " &
"characters than the minimum allowed length {2}.",
value, value.Length, MinLength))
End If
If value.Length > MaxLength Then
Throw New ArgumentException(String.Format("Provided string {0} of length {1} contains more " &
"characters than the maximum allowed length {2}.",
value, value.Length, MaxLength))
End If
If Not AllowNull AndAlso value Is Nothing Then
Throw New ArgumentNullException(String.Format("Provided string {0} is null, and null values " &
"are not allowed.", value))
End If
mstrValue = value
End Set
End Property
Private mintMinLength As Integer
''' <summary>
''' The minimum number of characters in this <see cref="BoundedString" />.
''' </summary>
Public Property MinLength() As Integer
Get
Return mintMinLength
End Get
Private Set(value As Integer)
mintMinLength = value
End Set
End Property
Private mintMaxLength As Integer
''' <summary>
''' The maximum number of characters in this <see cref="BoundedString" />.
''' </summary>
Public Property MaxLength As Integer
Get
Return mintMaxLength
End Get
Private Set(value As Integer)
mintMaxLength = value
End Set
End Property
Private mblnAllowNull As Boolean
''' <summary>
''' Whether or not this <see cref="BoundedString" /> can represent a null value.
''' </summary>
Public Property AllowNull As Boolean
Get
Return mblnAllowNull
End Get
Private Set(value As Boolean)
mblnAllowNull = value
End Set
End Property
Public Sub New(ByVal strValue As String,
ByVal intMaxLength As Integer)
MinLength = 0
MaxLength = intMaxLength
AllowNull = False
Value = strValue
End Sub
Public Sub New(ByVal strValue As String,
ByVal intMinLength As Integer,
ByVal intMaxLength As Integer)
MinLength = intMinLength
MaxLength = intMaxLength
AllowNull = False
Value = strValue
End Sub
Public Sub New(ByVal strValue As String,
ByVal intMinLength As Integer,
ByVal intMaxLength As Integer,
ByVal blnAllowNull As Boolean)
MinLength = intMinLength
MaxLength = intMaxLength
AllowNull = blnAllowNull
Value = strValue
End Sub
End Class
回答by Daniel Neel
This hasn't been fully tested, but here's a class to solve this problem:
这还没有经过全面测试，但这里有一个类可以解决这个问题：
Dim strBuff as String
回答by Adriaan Stander
Have you tried
你有没有尝试过
##代码##Also see Working with Strings in .NET using VB.NET
This tutorial explains how to represent strings in .NET using VB.NET and how to work with them with the help of .NET class library classes.
本教程解释了如何使用 VB.NET 在 .NET 中表示字符串，以及如何在 .NET 类库类的帮助下使用它们。
