Question

我的所有数据（名称/ rollnumber / class）都是固定长度（14个字节），我希望程序继续从数组中取一个随机名称，然后制作一个随机的rollnumber并继续将其写入文件直到我按下＆＃34; A＆＃34;。

运行完程序后，前14个字节始终为空，然后我的数据在接下来的14个字节中。更不用说了。我不知道为什么它只写了一个数据记录。

这是我的代码：

    Dim randomvalue As Integer

    'Making this array so that each data entry has 14 bytes to it

    Dim array1(91) As Integer

    array1(1) = 14
    For x = 2 To 91
        array1(x) = array1(x) + 14
    Next

    Dim n1, n2, n3, n4 As Integer

    'Array with names of fixed lenght, I want to take a name from only these 9:

    Dim array2(9) As String
    array2(1) = "aleen"
    array2(2) = "talha"
    array2(3) = "waddi"
    array2(4) = "hasna"
    array2(5) = "hassa"
    array2(6) = "zainn"
    array2(7) = "faqeh"
    array2(8) = "furru"
    array2(9) = "ibrah"

  'There is a structure above submain with studentname/rollnumber/class all declared as string 

    Dim newstudent As student
    Dim studentstream As New FileStream("C:\Users\Students\Desktop\A2Filing.dat", FileMode.OpenOrCreate)
    Dim bw As New BinaryWriter(studentstream)

    While Console.ReadLine <> "A"
        Console.WriteLine("Press any key other than 'A' if you want to make another entry into the file")


        'CInt(Math.Floor((upperlimit - lowerlimit + 1) * Rnd())) + lowerlimit
        'Randomize a number b/w 1-9 to get a studentname from the array

        randomvalue = CInt(Math.Floor((9 - 1 + 1) * Rnd())) + 1
        newstudent.studentname = array2(randomvalue)

        n1 = Rnd() + (Rnd() * 50)
        n2 = Rnd() * 10
        n3 = Rnd() * 255
        n4 = Rnd() * Rnd()
        newstudent.rollnumber = Convert.ToString(Left(n1, 1) + Left(n2, 1) + Left(n3, 1) + Left(n4, 1))

        newstudent.studentclass = "A2"

        'Randomize a number between 91 and 1 to place the data in

        Dim randomvalue2 As Integer
        randomvalue2 = CInt(Math.Floor((91 - 1 + 1) * Rnd())) + 1
        studentstream.Position = array1(randomvalue2)


        bw.Write(newstudent.studentname)
        bw.Write(newstudent.rollnumber)
        bw.Write(newstudent.studentclass)
    End While

Answer 1

这里有一些注意事项：

{init}的<script> function scrollDown() { $('html, body').animate({scrollTop: $("footer").offset().top}, 200); } </script> <a href="javascript: void(0);" onclick="javascript:scrollDown();">Click</a>项都是14，你必须把它改成以下，但正如我后面说的那样，不需要定义这样的数组！
```
array1
```
在For x = 2 To 91 array1(x) = array1(x - 1) + 14 'modified to array1(x - 1) Next之前，您有：bw.Write将覆盖文件位置！ studentstream.Position = array1(randomvalue2)中的所有项目都等于14.这就是为什么你总是得到一个小文件大小（仅此而已）。你不需要这样设置位置。 只需从代码中删除该行即可逐个添加数据。
根据文档，如果您使用array1来编写字符串，它将以字符串长度为前缀！ see this question。
```
BinaryWriter
```
如果要编写不带长度前缀的字符串，可以使用Dim bw As New BinaryWriter(studentstream, System.Text.Encoding.ASCII) bw.Write("A") 'writes: 1 A => where 1 is length of string "A" bw.Write("BC") 'writes: 2 B => where 2 is length of string "BC" 'note that for Unicode Encoding, it will be 2 bytes per char Dim bw As New BinaryWriter(studentstream, System.Text.Encoding.Unicode) bw.Write("A") '2 A 0 where 2 is length of unicde string [A 0] bw.Write("BC") '4 B 0 C 0 where 4 is length of unicde string [B 0 C 0]将其转换为字节数组：
```
System.Text.Encoding.ASCII.GetBytes(str)
```
另一种选择也是使用bw.Write(System.Text.Encoding.ASCII.GetBytes(newstudent.studentname))代替StreamWriter，因为您似乎不需要它。 see this link
请注意，使用BinaryWriter块打开文件会更好。否则，完成后不要忘记调用Using方法（Close）。如果你不这样做，你可能会失去最后一块或整个数据！
```
studentstream.Close()
```
使用Using studentstream As New FileStream("C:\...\Desktop\A2Filing.dat", FileMode.Create)覆盖文件（如果文件已存在）

我无法在循环中将数据写入二进制文件

1 个答案: