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<h1 id="eof-function">EOF Function</h1>
<p>Returns a Boolean value indicating whether the end of a file opened for Random or sequential
Input has been reached.</p>
<h2 id="syntax">Syntax</h2>
<pre><code class="language-vbnet">EOF(filenumber)</code></pre>
<h2 id="parameters">Parameters</h2>
<ul>
<li><strong>filenumber</strong>: Required. An Integer containing a valid file number.</li>
</ul>
<h2 id="return-value">Return Value</h2>
<p>Returns a Boolean value. Returns True when the end of a file opened for Random or Input
access has been reached; otherwise, returns False.</p>
<h2 id="remarks">Remarks</h2>
<p>The <code>EOF</code> function is used to detect when the end of a file has been reached during
sequential or random file reading operations. It's essential for controlling loops that
read through files.
<strong>Important Characteristics:</strong>
- Returns True when end of file is reached
- Returns False when more data is available
- Works with files opened for Input or Random access
- Does not work with files opened for Output or Append
- Does not work with binary mode files (use LOF instead)
- File must be open before calling EOF
- Error if file number is invalid or file is closed
- Position-dependent (affected by Get, Input, Line Input)
- Can be used to prevent "Input past end of file" error</p>
<h2 id="file-access-modes">File Access Modes</h2>
<ul>
<li><strong>Input</strong>: Sequential text file reading - EOF returns True after last character</li>
<li><strong>Random</strong>: Random access files - EOF returns True after last record</li>
<li><strong>Binary</strong>: Not supported (use LOF and Seek instead)</li>
<li><strong>Output/Append</strong>: Not applicable (write modes)</li>
</ul>
<h2 id="examples">Examples</h2>
<h3 id="basic-usage">Basic Usage</h3>
<pre><code class="language-vbnet">' Read text file line by line
Dim fileNum As Integer
Dim line As String
fileNum = FreeFile
Open "C:\data.txt" For Input As #fileNum
Do Until EOF(fileNum)
Line Input #fileNum, line
Debug.Print line
Loop
Close #fileNum</code></pre>
<h3 id="read-all-lines-into-array">Read All Lines into Array</h3>
<pre><code class="language-vbnet">Function ReadAllLines(filePath As String) As Variant
Dim fileNum As Integer
Dim lines() As String
Dim line As String
Dim count As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
count = 0
ReDim lines(0 To 100)
Do Until EOF(fileNum)
Line Input #fileNum, line
lines(count) = line
count = count + 1
If count > UBound(lines) Then
ReDim Preserve lines(0 To UBound(lines) + 100)
End If
Loop
Close #fileNum
If count > 0 Then
ReDim Preserve lines(0 To count - 1)
ReadAllLines = lines
Else
ReadAllLines = Array()
End If
End Function</code></pre>
<h3 id="random-access-file">Random Access File</h3>
<pre><code class="language-vbnet">Type CustomerRecord
ID As Long
Name As String * 50
Balance As Double
End Type
Sub ReadAllCustomers()
Dim fileNum As Integer
Dim customer As CustomerRecord
fileNum = FreeFile
Open "customers.dat" For Random As #fileNum Len = Len(customer)
Do Until EOF(fileNum)
Get #fileNum, , customer
Debug.Print customer.ID, customer.Name, customer.Balance
Loop
Close #fileNum
End Sub</code></pre>
<h2 id="common-patterns">Common Patterns</h2>
<h3 id="count-lines-in-file">Count Lines in File</h3>
<pre><code class="language-vbnet">Function CountLines(filePath As String) As Long
Dim fileNum As Integer
Dim line As String
Dim count As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
count = 0
Do Until EOF(fileNum)
Line Input #fileNum, line
count = count + 1
Loop
Close #fileNum
CountLines = count
End Function</code></pre>
<h3 id="search-file-for-text">Search File for Text</h3>
<pre><code class="language-vbnet">Function FindInFile(filePath As String, searchText As String) As Boolean
Dim fileNum As Integer
Dim line As String
fileNum = FreeFile
Open filePath For Input As #fileNum
FindInFile = False
Do Until EOF(fileNum)
Line Input #fileNum, line
If InStr(1, line, searchText, vbTextCompare) > 0 Then
FindInFile = True
Exit Do
End If
Loop
Close #fileNum
End Function</code></pre>
<h3 id="read-csv-file">Read CSV File</h3>
<pre><code class="language-vbnet">Function ReadCSV(filePath As String) As Variant
Dim fileNum As Integer
Dim line As String
Dim rows() As Variant
Dim rowCount As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
rowCount = 0
ReDim rows(0 To 100)
Do Until EOF(fileNum)
Line Input #fileNum, line
rows(rowCount) = Split(line, ",")
rowCount = rowCount + 1
If rowCount > UBound(rows) Then
ReDim Preserve rows(0 To UBound(rows) + 100)
End If
Loop
Close #fileNum
If rowCount > 0 Then
ReDim Preserve rows(0 To rowCount - 1)
ReadCSV = rows
Else
ReadCSV = Array()
End If
End Function</code></pre>
<h3 id="process-file-with-progress">Process File with Progress</h3>
<pre><code class="language-vbnet">Sub ProcessFileWithProgress(filePath As String)
Dim fileNum As Integer
Dim line As String
Dim lineCount As Long
Dim processedCount As Long
' Count total lines first
lineCount = CountLines(filePath)
fileNum = FreeFile
Open filePath For Input As #fileNum
processedCount = 0
Do Until EOF(fileNum)
Line Input #fileNum, line
ProcessLine line
processedCount = processedCount + 1
' Update progress
If processedCount Mod 100 = 0 Then
lblProgress.Caption = processedCount & " of " & lineCount
DoEvents
End If
Loop
Close #fileNum
End Sub</code></pre>
<h3 id="read-until-marker">Read Until Marker</h3>
<pre><code class="language-vbnet">Function ReadUntilMarker(fileNum As Integer, marker As String) As String
Dim line As String
Dim content As String
content = ""
Do Until EOF(fileNum)
Line Input #fileNum, line
If line = marker Then
Exit Do
End If
content = content & line & vbCrLf
Loop
ReadUntilMarker = content
End Function</code></pre>
<h3 id="skip-header-lines">Skip Header Lines</h3>
<pre><code class="language-vbnet">Sub ProcessDataFile(filePath As String, headerLines As Integer)
Dim fileNum As Integer
Dim line As String
Dim i As Integer
fileNum = FreeFile
Open filePath For Input As #fileNum
' Skip header lines
For i = 1 To headerLines
If Not EOF(fileNum) Then
Line Input #fileNum, line
End If
Next i
' Process remaining data
Do Until EOF(fileNum)
Line Input #fileNum, line
ProcessDataLine line
Loop
Close #fileNum
End Sub</code></pre>
<h3 id="read-fixed-number-of-lines">Read Fixed Number of Lines</h3>
<pre><code class="language-vbnet">Function ReadLines(filePath As String, maxLines As Long) As Variant
Dim fileNum As Integer
Dim lines() As String
Dim line As String
Dim count As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
ReDim lines(0 To maxLines - 1)
count = 0
Do Until EOF(fileNum) Or count >= maxLines
Line Input #fileNum, line
lines(count) = line
count = count + 1
Loop
Close #fileNum
If count > 0 Then
ReDim Preserve lines(0 To count - 1)
ReadLines = lines
Else
ReadLines = Array()
End If
End Function</code></pre>
<h3 id="merge-multiple-files">Merge Multiple Files</h3>
<pre><code class="language-vbnet">Sub MergeFiles(inputFiles As Variant, outputFile As String)
Dim outNum As Integer
Dim inNum As Integer
Dim i As Integer
Dim line As String
outNum = FreeFile
Open outputFile For Output As #outNum
For i = LBound(inputFiles) To UBound(inputFiles)
inNum = FreeFile
Open inputFiles(i) For Input As #inNum
Do Until EOF(inNum)
Line Input #inNum, line
Print #outNum, line
Loop
Close #inNum
Next i
Close #outNum
End Sub</code></pre>
<h3 id="filter-file-contents">Filter File Contents</h3>
<pre><code class="language-vbnet">Sub FilterFile(inputFile As String, outputFile As String, filterText As String)
Dim inNum As Integer
Dim outNum As Integer
Dim line As String
inNum = FreeFile
Open inputFile For Input As #inNum
outNum = FreeFile
Open outputFile For Output As #outNum
Do Until EOF(inNum)
Line Input #inNum, line
If InStr(1, line, filterText, vbTextCompare) > 0 Then
Print #outNum, line
End If
Loop
Close #inNum
Close #outNum
End Sub</code></pre>
<h2 id="advanced-usage">Advanced Usage</h2>
<h3 id="parse-configuration-file">Parse Configuration File</h3>
<pre><code class="language-vbnet">Function ParseConfigFile(filePath As String) As Collection
Dim fileNum As Integer
Dim line As String
Dim config As New Collection
Dim equalPos As Integer
Dim key As String
Dim value As String
fileNum = FreeFile
Open filePath For Input As #fileNum
Do Until EOF(fileNum)
Line Input #fileNum, line
line = Trim(line)
' Skip empty lines and comments
If Len(line) > 0 And Left(line, 1) <> "#" Then
equalPos = InStr(line, "=")
If equalPos > 0 Then
key = Trim(Left(line, equalPos - 1))
value = Trim(Mid(line, equalPos + 1))
On Error Resume Next
config.Add value, key
On Error GoTo 0
End If
End If
Loop
Close #fileNum
Set ParseConfigFile = config
End Function</code></pre>
<h3 id="read-log-file-with-timestamp-filter">Read Log File with Timestamp Filter</h3>
<pre><code class="language-vbnet">Function ReadLogsSince(logFile As String, sinceDate As Date) As Variant
Dim fileNum As Integer
Dim line As String
Dim logs() As String
Dim count As Long
Dim lineDate As Date
fileNum = FreeFile
Open logFile For Input As #fileNum
count = 0
ReDim logs(0 To 100)
Do Until EOF(fileNum)
Line Input #fileNum, line
' Assuming timestamp is first 19 chars: "2025-11-21 10:30:45"
If Len(line) >= 19 Then
On Error Resume Next
lineDate = CDate(Left(line, 19))
If Err.Number = 0 And lineDate >= sinceDate Then
logs(count) = line
count = count + 1
If count > UBound(logs) Then
ReDim Preserve logs(0 To UBound(logs) + 100)
End If
End If
On Error GoTo 0
End If
Loop
Close #fileNum
If count > 0 Then
ReDim Preserve logs(0 To count - 1)
ReadLogsSince = logs
Else
ReadLogsSince = Array()
End If
End Function</code></pre>
<h3 id="batch-process-multiple-files">Batch Process Multiple Files</h3>
<pre><code class="language-vbnet">Sub BatchProcessFiles(filePattern As String)
Dim fileName As String
Dim fileNum As Integer
Dim line As String
Dim processedCount As Long
fileName = Dir(filePattern)
Do While fileName <> ""
fileNum = FreeFile
Open fileName For Input As #fileNum
Do Until EOF(fileNum)
Line Input #fileNum, line
ProcessLine line
Loop
Close #fileNum
processedCount = processedCount + 1
fileName = Dir
Loop
MsgBox processedCount & " files processed"
End Sub</code></pre>
<h3 id="read-file-in-chunks">Read File in Chunks</h3>
<pre><code class="language-vbnet">Function ReadFileChunk(fileNum As Integer, chunkSize As Long) As Variant
Dim lines() As String
Dim line As String
Dim count As Long
ReDim lines(0 To chunkSize - 1)
count = 0
Do Until EOF(fileNum) Or count >= chunkSize
Line Input #fileNum, line
lines(count) = line
count = count + 1
Loop
If count > 0 Then
ReDim Preserve lines(0 To count - 1)
ReadFileChunk = lines
Else
ReadFileChunk = Array()
End If
End Function
' Usage with pagination
Sub ProcessLargeFile(filePath As String)
Dim fileNum As Integer
Dim chunk As Variant
Dim pageNum As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
pageNum = 1
Do Until EOF(fileNum)
chunk = ReadFileChunk(fileNum, 1000)
ProcessChunk chunk, pageNum
pageNum = pageNum + 1
Loop
Close #fileNum
End Sub</code></pre>
<h3 id="database-import-from-text-file">Database Import from Text File</h3>
<pre><code class="language-vbnet">Sub ImportDataFromFile(filePath As String, tableName As String)
Dim fileNum As Integer
Dim line As String
Dim fields() As String
Dim sql As String
Dim recordCount As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
' Skip header
If Not EOF(fileNum) Then
Line Input #fileNum, line
End If
recordCount = 0
Do Until EOF(fileNum)
Line Input #fileNum, line
fields = Split(line, vbTab)
sql = "INSERT INTO " & tableName & " VALUES ('" & _
Join(fields, "','") & "')"
' Execute SQL (pseudo-code)
ExecuteSQL sql
recordCount = recordCount + 1
Loop
Close #fileNum
MsgBox recordCount & " records imported"
End Sub</code></pre>
<h3 id="create-file-index">Create File Index</h3>
<pre><code class="language-vbnet">Type FileIndex
LineNumber As Long
FilePosition As Long
Content As String
End Type
Function BuildFileIndex(filePath As String) As Variant
Dim fileNum As Integer
Dim index() As FileIndex
Dim line As String
Dim count As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
count = 0
ReDim index(0 To 100)
Do Until EOF(fileNum)
index(count).LineNumber = count + 1
index(count).FilePosition = Seek(fileNum)
Line Input #fileNum, line
index(count).Content = Left(line, 100) ' Store first 100 chars
count = count + 1
If count > UBound(index) Then
ReDim Preserve index(0 To UBound(index) + 100)
End If
Loop
Close #fileNum
If count > 0 Then
ReDim Preserve index(0 To count - 1)
BuildFileIndex = index
Else
BuildFileIndex = Array()
End If
End Function</code></pre>
<h2 id="error-handling">Error Handling</h2>
<pre><code class="language-vbnet">Function SafeReadFile(filePath As String) As Variant
On Error GoTo ErrorHandler
Dim fileNum As Integer
Dim lines() As String
Dim line As String
Dim count As Long
fileNum = FreeFile
Open filePath For Input As #fileNum
count = 0
ReDim lines(0 To 100)
Do Until EOF(fileNum)
Line Input #fileNum, line
lines(count) = line
count = count + 1
If count > UBound(lines) Then
ReDim Preserve lines(0 To UBound(lines) + 100)
End If
Loop
Close #fileNum
If count > 0 Then
ReDim Preserve lines(0 To count - 1)
SafeReadFile = lines
Else
SafeReadFile = Array()
End If
Exit Function
ErrorHandler:
If fileNum > 0 Then Close #fileNum
SafeReadFile = Null
End Function</code></pre>
<h3 id="common-errors">Common Errors</h3>
<ul>
<li><strong>Error 52</strong> (Bad file name or number): File number is invalid or file is closed</li>
<li><strong>Error 62</strong> (Input past end of file): Attempted to read beyond EOF without checking</li>
<li><strong>Error 54</strong> (Bad file mode): File not opened for Input or Random access</li>
</ul>
<h2 id="performance-considerations">Performance Considerations</h2>
<ul>
<li><code>EOF</code> is very fast (single status check)</li>
<li>No performance penalty for frequent calls</li>
<li>Use <code>Do Until EOF</code> rather than counting lines beforehand</li>
<li>For large files, consider buffered reading</li>
<li>Random access files: EOF checks record position</li>
<li>Sequential files: EOF checks character position</li>
</ul>
<h2 id="best-practices">Best Practices</h2>
<h3 id="always-use-eof-to-control-file-reading">Always Use EOF to Control File Reading</h3>
<pre><code class="language-vbnet">' Good - Use EOF to detect end
Do Until EOF(fileNum)
Line Input #fileNum, line
ProcessLine line
Loop
' Bad - May cause "Input past end of file" error
Do While True
Line Input #fileNum, line ' Error if EOF reached
ProcessLine line
Loop</code></pre>
<h3 id="always-close-files">Always Close Files</h3>
<pre><code class="language-vbnet">' Good - Always close, even on error
On Error GoTo ErrorHandler
Open filePath For Input As #fileNum
Do Until EOF(fileNum)
' Process
Loop
Close #fileNum
Exit Sub
ErrorHandler:
If fileNum > 0 Then Close #fileNum</code></pre>
<h3 id="check-eof-before-reading">Check EOF Before Reading</h3>
<pre><code class="language-vbnet">' Good - Check before reading
If Not EOF(fileNum) Then
Line Input #fileNum, line
End If
' Or use in loop condition
Do Until EOF(fileNum)
Line Input #fileNum, line
Loop</code></pre>
<h2 id="comparison-with-other-methods">Comparison with Other Methods</h2>
<h3 id="eof-vs-lof">EOF vs LOF</h3>
<pre><code class="language-vbnet">' EOF - Detects end of file for Input/Random
Do Until EOF(fileNum)
Line Input #fileNum, line
Loop
' LOF - Gets file length (useful for Binary mode)
Open file For Binary As #fileNum
fileSize = LOF(fileNum)</code></pre>
<h3 id="eof-vs-seek">EOF vs Seek</h3>
<pre><code class="language-vbnet">' EOF - Boolean end-of-file check
isAtEnd = EOF(fileNum)
' Seek - Get/set current position
currentPos = Seek(fileNum)</code></pre>
<h2 id="limitations">Limitations</h2>
<ul>
<li>Only works with Input and Random access modes</li>
<li>Not applicable to Binary mode (use LOF and Seek)</li>
<li>Not applicable to Output or Append modes</li>
<li>Does not indicate how much data remains</li>
<li>File must be open</li>
<li>Cannot detect EOF before opening file</li>
</ul>
<h2 id="related-functions">Related Functions</h2>
<ul>
<li><code>LOF</code>: Returns length of file in bytes</li>
<li><code>Seek</code>: Returns or sets current position in file</li>
<li><code>Open</code>: Opens file for reading/writing</li>
<li><code>Close</code>: Closes open file</li>
<li><code>Line Input</code>: Reads line from file</li>
<li><code>Input</code>: Reads data from file</li>
<li><code>Get</code>: Reads data from random/binary file</li>
<li><code>FreeFile</code>: Returns next available file number</li>
</ul>
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