Searchi an array

[torg]

I`ve been sitting here for a while now, but can`t figure out what I`m doing wrong. I`m hoping that someone out here can help me to solve my problem. I receive the message. that there are noe object reference set to this instance of object. Can anybody tell meg Why?

Ive got:

Structure individual
       Dim name1 As String
       Dim dato As String
       Dim address As String
       Dim Phonenumber As String
   End Structure

   Dim Person(100) As individual
  Dim numPosts as integer

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    
            Dim sr As StreamReader = File.OpenText("Personalia.txt")
       Do While (sr.Peek <> -1) And (numPosts< Person.GetUpperBound(0))

           numPosts += 1
           Person(numPosts ).name1 = sr.ReadLine
           Person(numPosts ).dato = sr.ReadLine
           Person(numPosts ).address = sr.ReadLine
           Person(numPosts ).Phonenumber = sr.ReadLine
       Loop
....
end sub

Function FindName(ByVal name1) As String
       Dim sr As StreamReader = File.OpenText("Personalia.txt")
       Dim First, Mid, Last As Integer

       Dim foundFlag As Boolean
       First= 1
       Last= numPosts
       Do While (first<= last) And (Not foundFlag)
           Mid= CInt((first+ last) / 2)
           Select Case Person(Mid).name1.ToUpper
               Case name
                   foundFlag = True 
               Case Is > name1
                   last= first- 1
               Case Is < name1
                   last= first+ 1
           End Select
          Loop

       If foundFlag Then
           ListBox1.Items.Add(Person(mid).name1)
       Else
           MessageBox.Show("nothing")
       End If
   End Function

[PlausiblyDamp]

I notice you are incrementing a variable called antPoster in the While loop but it doesn't appear to be declared anywhere, on a related note you are not incrementing the numPosts variable within the loop and as such you are just going to keep overwriting the first element in the array.

[torg]

Sorry, that was just a write fault. antPosts is numPosts..As it is in my original code. (had to do some amendments before copying the code to this board) So problem is stilll here...

[PlausiblyDamp]

What is the problem exactly?

[nibsy]

Try

 

Dim sr AS StreamReader 

sr = New StreamReader(New FileStream("Personalia.txt"), FileMode.Open))

 

I hope this helps

 

:)

[torg]

I receive the following message when trying your proposal. overload resolution failed because no accessible 'New' accepts the number of arguments.

I`ve used

Dim sr As StreamReader = File.OpenText("Personalia.txt")

other places in my code, and have not had any problems with that. so I doubt that`s my problem. If it is there must be another answer to it.

[nibsy]

Sorry, I lead you astray:

 

Can you try?

 

Dim sr As StreamReader 
Dim fs As FileStream

fs = New New FileStream(("Personalia.txt"),  FileMode.Open)
sr = New StreamReader(fs)

[torg]

Doesn`t help either.

i`m using

Option Explicit On 
Imports System.IO
Public Class Form4

in the top of my programming code, så I don`t see that what you suggest would help very much.

 

My problem is.: I`ve got at file "txtPersonalia.txt" where you can get certain information. this informatiin are to be placed into an array on form load where it will be sorted in an ascending order .When I type a text in a textbox, the file will be searched to find a match, and write all information that is relevant for that reslut

 

  Structure individual
       Dim name As String
       Dim dato As String
       Dim address As String
       Dim Phonnumber As String
   End Structure

   Dim Person(100) As individual

 

when trying to run I receive the following message

Additional information: Object reference not set to an instance of an object. Which drives me crazy

[mutant]

What line do you get the error on?

[torg]

at this line:

Select Case Person(Mid).name1.ToUpper

[PlausiblyDamp]

What is the value of mid at the time of the error?

Also when you get the error what is the value of Person(mid)?

[torg]

50 on both of them

[PlausiblyDamp]

is Person(50).name1 a valid string?

[torg]

I`m not sure I understand what you`re asking about.

The array reads data from a file , as long as ithere are "Data" to read. If there are only 49 posts in the file, then the arrayindex 50 would be empty.As is the case in my example. I`ve only registered 6 Posts/persons in the file.

[PlausiblyDamp]

the problem is probably the fact that the line

Mid= CInt((first+ last) / 2)

 

will always equal 50 on the first run through regardless of how many items you've read from the file. You would probably need to have a seperate variable to keep track of the number of valid records read rather than just basing it on the size of the array.

If you still have a problem reply and I'll try to knock a sample together.

[torg]

I would appreciate an example :)

[PlausiblyDamp]

Just a few other things.

I notice you are opening a StreamReader in the first line of the FindName function - did you mean to?

 

Also within the select case statement you have a lne that reads

Case Name

 

should that be

Case Name1

instead?

 

also you appear to be doing a binary search of the data - am I correct?

If so is the data sorted? If so are the blank entries being moved to the start of the array rather than the end?

 

finally are you modifying the numPosts variable anywhere else in the Form_Load?

[torg]

Yes, that should be Case Name1. Yes, it`s supposted to be a binarysearch of the data And no, the streamreader was not supposted to be in the function.

 

I`ve never taken into concern to move blank fields to the end or start. How do I do that?

 

The posts in the file are already sorted alphabeticalla by name

But that`s just while trying to get the code to work. I`m going to use the sort algorithm downbelow

 

As you`ll see downbelow, It`s only in the sort algorithm where I use the variable except from in the FindName function. But it`s not modified there.

 

Sub sort()
        Dim gap As Integer, doneFlag As Boolean
       Dim index As Integer, temp As String
       gap = CInt(numPosts/ 2)

       Do While gap >= 1
           Do
               doneFlag = True
               For index = 1 To numPosts- gap
                   If person(index).name1> person(index + gap).name1 Then
                       temp = person(index).name1
                       person(index).name1= person(index + gap).name1
                       person(index + gap).name1 = temp
                       doneFlag = False
                   End If
               Next
           Loop Until doneFlag = True
           gap = CInt(gap / 2)
       Loop
   End Sub

 

There may be some write faults in the code that may have occured during translation of code. Ignore them. Or assume the syntax is correct.

[ccc]

I may be stating the obvious, but make sure your string, is actually filled with something before you try calling ToUpper.

 

Dim testStr As String
MsgBox(testStr.ToUpper)'Would error

Dim testStr As String = ""
MsgBox(testStr.ToUpper)'Would not error

Dim testStr As String
MsgBox(UCase(testStr))'Would not error

 

 

I stay away from using ToUpper, ToLower, Trim, Length of the string object because of this, and I use functions themselves. :eek:

[torg]

I`ve used

If IsNothing(individ(i).navn) Then individ(i).navn = ""

in the form_load procedure.

Still there is something wrong. It seems as if there are not performed any search at all, atleast no result are shown

 

the search algorithm now looks like this:

Function findName(ByVal name2 As String) As Integer
       Dim first, middle, last As Integer
       first = 0
       last = numOfRecords
       Do While (first <= last)
           middle = CInt((first + last) / 2)
           Select Case UCase(Person(middle).name1) 
               Case name2
                   Return middle
               Case Is > name2
                   last = middle - 1
               Case Is < name2
                   first = middle + 1
           End Select
       Loop
       Return 0
   End Function

[PlausiblyDamp]

I just tried a simple test app using your code and I changed the line

Case name2

to

Case name2.ToUpper

and things worked.