要解压缩ZIP文件，所以肯定需要读写文件的功能，为了方便，把VBA中对文件的读写功能进行一个简单的封装，方便使用。
ZIP文件压缩后，保存数据使用的最小单位是bit，注意不是Byte，计算机的1Byte=8bit，正常在VBA中操作的最小单位是Byte，为了方便读取bit位的数据，写几个简单的函数。
01
CFile文件读写
主要是使用类模块对文件操作Open、Put、Get等关键字的简单封装，这样使用起来就更加的方便。
代码语言：javascript复制Public Enum OpenAccess
O_RDONLY
O_WRONLY
O_RDWR
End Enum
Public Enum SeekPos
OriginF
CurrentF
EndF
End Enum
'注意大文件long类型会溢出
Private lFileLen As Long
Private num_file As Integer
'写入文件
Function WriteFile(b() As Byte) As Long
Put #num_file, , b
End Function
'读取len(b)个byte
Function Read(b() As Byte) As Long
Dim ilen As Long
ilen = UBound(b) - LBound(b) 1
Dim iseek As Long
iseek = VBA.Seek(num_file)
If iseek ilen > lFileLen Then
ilen = lFileLen - iseek 1
End If
Get #num_file, , b
Read = ilen
End Function
'读取一个2Byte的整数
Function ReadInteger() As Integer
Dim i As Integer
Get #num_file, , i
ReadInteger = i
End Function
'读取1个4Byte的整数
Function ReadLong() As Long
Dim i As Long
Get #num_file, , i
ReadLong = i
End Function
'在offset处开始读取
Function ReadAt(b() As Byte, offset As Long) As Long
SeekFile offset, 0
ReadAt = Read(b)
End Function
'设置读取的位置
Function SeekFile(offset As Long, whence As SeekPos) As Long
Dim iseek As Long
iseek = VBA.Seek(num_file)
'vba Seek是下标1开始
If whence = SeekPos.OriginF Then
iseek = 1 offset
ElseIf whence = SeekPos.CurrentF Then
iseek = iseek offset
Else
iseek = 1 lFileLen - offset
End If
Seek #num_file, iseek
SeekFile = iseek
End Function
'以字节方式读取文本
Function OpenFile(Filename As String, Optional m As OpenAccess = OpenAccess.O_RDWR) As Long
'避免多次调用OpenFile的时候，前面的文件未关闭
If num_file Then Close #num_file
num_file = VBA.FreeFile
Select Case m
Case OpenAccess.O_RDONLY
Open Filename For Binary Access Read As #num_file
Case OpenAccess.O_WRONLY
Open Filename For Binary Access Write As #num_file
Case OpenAccess.O_RDWR
Open Filename For Binary Access Read Write As #num_file
Case Else
End Select
lFileLen = VBA.FileLen(Filename)
End Function
Function CloseFile()
Close #num_file
End Function
Private Sub Class_Terminate()
CloseFile
End Sub02
bit位操作
计算机中1Byte=8bit，bit的排列顺序和数学中的个位、十位、百位……是一样的：
解压ZIP的过程中，需要不停的从压缩数据的Byte数组中读取需要的bit，实现几个简单的函数：
代码语言：javascript复制'取某一位的Bit
Function GetBitFromByte(b As Byte, ZeroBaseIndex As Long) As Long
GetBitFromByte = VBA.CLng(b) And (2 ^ ZeroBaseIndex)
If GetBitFromByte > 0 Then
GetBitFromByte = 1
Else
GetBitFromByte = 0
End If
End Function'从Byte数组中取某一位的Bit
Function GetBit(b() As Byte, ZeroBaseIndex As Long) As Long
'数组b中，开始的下标
Dim bindex As Long
bindex = ZeroBaseIndex 8
GetBit = VBA.CLng(b(bindex)) And (2 ^ (ZeroBaseIndex Mod 8))
If GetBit > 0 Then
GetBit = 1
Else
GetBit = 0
End If
End Function'从Byte数组中取多位bit
' 0000 0000 0000 0000
' 7654 3210 fedc ba98
Function GetBits(b() As Byte, IndexFromZeroBase As Long, iBits As Long) As Long
Dim i As Long
Dim tmp As Long
For i = 0 To iBits - 1
tmp = GetBit(b, IndexFromZeroBase i)
tmp = BitMoveLeft(tmp, i)
GetBits = GetBits Or tmp
Next
End Function
'左移
Function BitMoveLeft(ByRef l As Long, num As Long) As Long
Dim i As Long
For i = 1 To num
'会溢出 0x7FFF FFFF
'判断第31位是否=1
'不管等不等于1都把第31为置换为0，负数待处理
l = l And &H3FFFFFFF
l = l * 2
Next
BitMoveLeft = l
End Function
'右移
Function BitMoveRight(ByRef l As Long, num As Long) As Long
Dim i As Long
For i = 1 To num
l = l 2
Next
BitMoveRight = l
End Function'从Byte数组中取多位bit
'取出后的bit存储顺序倒置
Function GetBitsRev(b() As Byte, IndexFromZeroBase As Long, iBits As Long) As Long
Dim i As Long
Dim tmp As Long
For i = 0 To iBits - 1
tmp = GetBit(b, IndexFromZeroBase i)
tmp = BitMoveLeft(tmp, iBits - i - 1)
GetBitsRev = GetBitsRev Or tmp
Next
End Function
