How to verify that a word exist on a .txt file using Visual Basic v6

Dim strBuffer As String
Open "c:\MyPath\Test.txt" For Input As #1
strBuffer = Input(LOF(1), 1)
If Instr(1, strBuffer, "example") Then
     MsgBox "It's there'
End If
Close #1

Here's better code with comments.


Dim strBuffer As String
' Define an Integer to hold the file number
Dim FF As Integer

' Find a file number that's not in use
FF = FreeFile

Open "c:\temp\Test.txt" For Input As #FF

' The format of 'Input' is Input(how-many-bytes, file-number) and
' LOF is Length Of File so how-many-bytes is set at length of the file
strBuffer = Input(LOF(FF), FF)
If InStr(1, strBuffer, "example") Then
     MsgBox "It's there'"
End If
Close #FF

Wouldn't doing InStr on a large file line by line be pretty slow.

As an alternative the file could be read in large chunks using Input.

But if you read it in chunks, a chunk might end in the middle of the text you are looking for.  By reading a line at a time, you are assured that each 'chunk' ends on a Carriage Return.

Besides, if your computer has good disk reading buffers, there should be a huge performance difference.

Either InStr searches something like 100 byte buffers 10,000 times, or it searches 10,000 byte buffers 100 times.  Either way InStr has to process 1,000,000 of memory.  Yes, there will be some performance boost because InStr is called fewer times with larger memory chunks (and the same can be said about disk reads).  But adding a few thousand function calls should affect over all speed greatly, so long as the disk reading logic has good buffering (because I/O is going to be your bottle neck, not multiple function calls).

But if you read it in chunks, a chunk might end in the middle of the text you are looking for.

Good point.