VB快速查找大型文件中包含的字符串
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关于查找大型文件中包含的字符串,一般都把文件内容读入到内存,然后在内存里进行比较,却不知这种办法有一个致命的弱点,那就是由于大量的内存申请和释放导致的内存颠簸,会使系统性能下降,严重影响了查找的速度。特别是在递归中对多个文件进行查找时,这个问题会更加突出,有时甚至会导致VB程序挂掉。为避免这种情况,同时加快大型文件中字符串的查找速度,俺基于内存影射文件和VB模拟指针技术,编写了一个通用字符串查找函数。
首先,先看一个普通的查找函数:
-
- Private Function FindText(ByVal strFileName As String, ByVal strText As String) As Long
- Dim fn As Integer
- Dim strFileText As String
-
- Dim MyString, MyNumber
- Dim S As String
-
- fn = FreeFile()
- Open strFileName For Binary As #fn
- strFileText = Input(LOF(fn), fn)
- Close #fn
- FindText = InStr(strFileText, strText)
- End Function
用一个400K的文本进行测试,测试次数为20次,测试代码如下:
- Sub Main()
- Dim lStartTime As Long
-
-
- lStartTime = GetTickCount
- Call FindText("G:/Inst/小说/沧海凤歌.txt", "打打秋风")
- Debug.Print GetTickCount - lStartTime
- End Sub
根据测试结果,最大耗时为2050ms,最小耗时为890ms,平均在950ms左右。
然后,我看再看一下基于内存影射和模拟指针的查找函数,代码如下:
- Option Explicit
-
- Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
- Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
- Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
- Private Declare Function GetFileSize Lib "kernel32" (ByVal hFile As Long, lpFileSizeHigh As Long) As Long
- Private Const GENERIC_READ = &H80000000
- Private Const GENERIC_WRITE = &H40000000
- Private Const OPEN_EXISTING = 3
- Private Const FILE_SHARE_READ = &H1
- Private Const FILE_SHARE_WRITE = &H2
- Private Const FILE_ATTRIBUTE_NORMAL = &H80
- Private Const FILE_ATTRIBUTE_ARCHIVE = &H20
- Private Const FILE_ATTRIBUTE_READONLY = &H1
- Private Const FILE_ATTRIBUTE_HIDDEN = &H2
- Private Const FILE_ATTRIBUTE_SYSTEM = &H4
-
- Private Declare Function CreateFileMapping Lib "kernel32" Alias "CreateFileMappingA" (ByVal hFile As Long, ByVal lpFileMappigAttributes As Long, ByVal flProtect As Long, ByVal dwMaximumSizeHigh As Long, ByVal dwMaximumSizeLow As Long, ByVal lpName As String) As Long
- Private Declare Function MapViewOfFile Lib "kernel32" (ByVal hFileMappingObject As Long, ByVal dwDesiredAccess As Long, ByVal dwFileOffsetHigh As Long, ByVal dwFileOffsetLow As Long, ByVal dwNumberOfBytesToMap As Long) As Long
- Private Declare Function UnmapViewOfFile Lib "kernel32" (lpBaseAddress As Any) As Long
- Private Const PAGE_READWRITE = &H4
- Private Const FILE_MAP_READ = &H4
-
- Private Declare Function VarPtrArray Lib "msvbvm60.dll" Alias "VarPtr" (Ptr() As Any) As Long
- Private Type SAFEARRAYBOUND
- cElements As Long
- lLbound As Long
- End Type
- Private Type SAFEARRAY1D
- cDims As Integer
- fFeatures As Integer
- cbElements As Long
- clocks As Long
- pvData As Long
- rgsabound(0) As SAFEARRAYBOUND
- End Type
-
-
- Function FindTextInFile(ByVal strFileName As String, ByVal strText As String) As Long
- Dim hFile As Long, hFileMap As Long
- Dim nFileSize As Long, lpszFileText As Long, pbFileText() As Byte
- Dim ppSA As Long, pSA As Long
- Dim tagNewSA As SAFEARRAY1D, tagOldSA As SAFEARRAY1D
-
- hFile = CreateFile(strFileName, _
- GENERIC_READ Or GENERIC_WRITE, _
- FILE_SHARE_READ Or FILE_SHARE_WRITE, _
- 0, _
- OPEN_EXISTING, _
- FILE_ATTRIBUTE_NORMAL Or FILE_ATTRIBUTE_ARCHIVE Or FILE_ATTRIBUTE_READONLY Or _
- FILE_ATTRIBUTE_HIDDEN Or FILE_ATTRIBUTE_SYSTEM, _
- 0)
- If hFile <> 0 Then
- nFileSize = GetFileSize(hFile, ByVal 0&)
- hFileMap = CreateFileMapping(hFile, 0, PAGE_READWRITE, 0, 0, vbNullString)
- lpszFileText = MapViewOfFile(hFileMap, FILE_MAP_READ, 0, 0, 0)
-
- ReDim pbFileText(0)
- ppSA = VarPtrArray(pbFileText)
- CopyMemory pSA, ByVal ppSA, 4
- CopyMemory tagOldSA, ByVal pSA, Len(tagOldSA)
- CopyMemory tagNewSA, tagOldSA, Len(tagNewSA)
- tagNewSA.rgsabound(0).cElements = nFileSize
- tagNewSA.pvData = lpszFileText
- CopyMemory ByVal pSA, tagNewSA, Len(tagNewSA)
-
- FindTextInFile = InStr(pbFileText, StrConv(strText, vbFromUnicode))
-
- CopyMemory ByVal pSA, tagOldSA, Len(tagOldSA)
- Erase pbFileText
-
- UnmapViewOfFile lpszFileText
- CloseHandle hFileMap
- End If
- CloseHandle hFile
- End Function
这个函数明显比上一个函数复杂得到,按理说,它运行速度肯定相应的要慢一些,咱们先不下定论,还是经过测试后再说吧,测试代码如下:
调用代码如下:
- Sub Main()
- lStartTime = GetTickCount
- Call FindTextInFile("G:/Inst/小说/沧海凤歌.txt", "打打秋风")
- Debug.Print GetTickCount - lStartTime
- End Sub
使用了同一个文本文件,同样测试了20次,嘿,第二个函数最大耗时为17ms,最小耗时为0ms,平均不超过1ms,这进一步验证了我的设计初衷。
如果你有更好的思路和建议,恳请告诉俺,俺在此表示感谢了!
原文链接 :http://blog.csdn.net/lyserver/article/details/4106290