在上一节的基础上,本节做一些扩展。
判断文件是什么类型,为了简化操作,仅仅只判断是否可执行文件、png文件、gif文件、jpeg文件。
上述文件对应的前面几个字节是:
可执行文件:4D 5A
PNG文件:89 50 4E 47
Jpeg文件:FF D8 FF E0 00 10 4A 46 49 46
gif89文件:47 49 46 38 39 61
需要说明的是,我没有真正去查找相关文件格式信息,这里只是为了说明二进制文件的读取,以上资料是用WinHex查看得来的,不一定就是真正的文件头,
相关代码如下:
Private Sub btnOpenFile_Click(sender As Object,e As EventArgs) Handles btnOpenFile.Click Dim filename As String If OpenFileDialog1.ShowDialog <> DialogResult.OK Then Exit Sub End If filename = OpenFileDialog1.FileName lblFilePath.Text = filename txtFileType.Text = checkFileType(filename) End Sub
具体实现代码:
Private Function checkFileType(ByVal filename As String) As String Try Dim fs As FileStream = New FileStream(filename,FileMode.Open) If fs.Length < 10 Then Return "未知文件" Dim br As BinaryReader = New BinaryReader(fs) Dim byteRead() As Byte Dim intReadLength As Integer = 10 ReDim byteRead(intReadLength - 1) byteRead = br.ReadBytes(intReadLength) br.Close() fs.Close() If byteRead(0) = Convert.ToInt32("4D",16) And byteRead(1) = Convert.ToInt32("5A",16) Then Return "可执行文件" If byteRead(0) = Convert.ToInt32("89",16) And byteRead(1) = Convert.ToInt32("50",16) And byteRead(2) = Convert.ToInt32("4E",16) _ And Convert.ToInt32("47",16) Then Return "PNG文件" If byteRead(0) = Convert.ToInt32("47",16) And byteRead(1) = Convert.ToInt32("49",16) And byteRead(2) = Convert.ToInt32("46",16) _ And byteRead(3) = Convert.ToInt32("38",16) And byteRead(4) = Convert.ToInt32("39",16) _ And byteRead(5) = Convert.ToInt32("61",16) Then Return "Gif文件" If byteRead(0) = Convert.ToInt32("FF",16) And byteRead(1) = Convert.ToInt32("D8",16) And byteRead(2) = Convert.ToInt32("FF",16) _ And byteRead(3) = Convert.ToInt32("E0",16) And byteRead(4) = Convert.ToInt32("00",16) _ And byteRead(5) = Convert.ToInt32("10",16) And byteRead(6) = Convert.ToInt32("4A",16) _ And byteRead(7) = Convert.ToInt32("46",16) And byteRead(8) = Convert.ToInt32("49",16) _ And byteRead(9) = Convert.ToInt32("46",16) Then Return "Jpeg文件" Return "" Catch ex As Exception Return "" End Try End Function
运行时如图:
由于二进制文件写入和读取比较类似,这里不再累述,
在下一节中,我们将学习做一个存档文件修改器,将会有二进制文件读写的详细代码。
由于.net平台下C#和vb.NET很相似,本文也可以为C#爱好者提供参考。
学习更多vb.net知识,请参看 vb.net 教程 目录