SQL Server对图像数据存储机制介绍(3)

Public Function ReadbolbToFile
(blobColumn As ADODB.Field, ByVal FileName) As Boolean
Dim FileNumber     As Integer     '文件号
Dim DataLen               As Long            '文件长度
Dim Chunks               As Long            '数据块数
Dim ChunkAry()     As Byte     '数据块数组
Dim ChunkSize      As Long            '数据块大小
Dim Fragment       As Long            '零碎数据大小
Dim lngI                   As Long  '计数器
    
           On Error GoTo ErrorHandle
           ReadbolbToFile= False
           ChunkSize = 2048                        '定义块大小为 2K
           If IsNull(blobColumn) Then Exit Function
    
           DataLen = blobColumn.ActualSize           '获得图像大小
           If DataLen < 8 Then  Exit Function    '图像大小小于8字节时认为不是图像信息
               FileNumber = FreeFile                      '产生随机的文件号
           Open FileName For Binary Access Write As FileNumber  '打开存放图像数据文件
           Chunks = DataLen \ ChunkSize         '数据块数
           Fragment = DataLen Mod ChunkSize   '零碎数据
           If Fragment > 0 Then                  '有零碎数据，则先读该数据
                      ReDim ChunkAry(Fragment - 1)
                      ChunkAry = blobColumn.GetChunk(Fragment)
                      Put FileNumber, , ChunkAry       '写入文件
           End If
    
           ReDim ChunkAry(ChunkSize - 1)             '为数据块重新开辟空间
           For lngI = 1 To Chunks                               '&shy;循环读出所有块
           ChunkAry = blobColumn.GetChunk(ChunkSize)   '在数据库中连续读数据块
                      Put FileNumber, , ChunkAry()     '将数据块写入文件中
           Next lngI
           Close FileNumber                 '关闭文件
           ReadbolbToFile= True
           Exit Function
ErrorHandle:
           ReadbolbToFile= False
           MsgBox Err.Description, vbCritical, "读图像数据出错!"
End Function