文件的读取VB6 方法二

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参考博客  https://blog.csdn.net/lyserver/article/details/4106290   lyserver的专栏

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




'使用内存映射方式查找大型文件中包含的字符串
'Function FindTextInFile(ByVal strFileName As String, ByVal strText As String) As String
Function getFilestring(ByVal strFileName As String) As String
    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) '打开文件
    If hFile <> 0 Then
        nFileSize = GetFileSize(hFile, ByVal 0&) '获得文件大小
        hFileMap = CreateFileMapping(hFile, 0, PAGE_READWRITE, 0, 0, vbNullString) '创建文件映射对象
        lpszFileText = MapViewOfFile(hFileMap, FILE_MAP_READ, 0, 0, 0) '将映射对象映射到进程内部的地址空间
       
        ReDim pbFileText(0) '初始化数组
        ppSA = VarPtrArray(pbFileText) '获得指向SAFEARRAY的指针的指针
        CopyMemory pSA, ByVal ppSA, 4 '获得指向SAFEARRAY的指针
        CopyMemory tagOldSA, ByVal pSA, Len(tagOldSA) '保存原来的SAFEARRAY成员信息
        CopyMemory tagNewSA, tagOldSA, Len(tagNewSA) '复制SAFEARRAY成员信息
        tagNewSA.rgsabound(0).cElements = nFileSize '修改数组元素个数
        tagNewSA.pvData = lpszFileText '修改数组数据地址
        CopyMemory ByVal pSA, tagNewSA, Len(tagNewSA) '将映射后的数据地址绑定至数组
       
       ' FindTextInFile = InStr(pbFileText, StrConv(strText, vbFromUnicode)) '查找子字符串位置
        getFilestring = StrConv(pbFileText, vbUnicode)
        CopyMemory ByVal pSA, tagOldSA, Len(tagOldSA) '恢复数组的SAFEARRAY结构成员信息
        Erase pbFileText '删除数组
       
        UnmapViewOfFile lpszFileText '取消地址映射
        CloseHandle hFileMap '关闭文件映射对象的句柄
    End If
    CloseHandle hFile '关闭文件
End Function