strreverse - String - VB6Parse Library Reference

VB6 StrReverse Function

The StrReverse function returns a string in which the character order of a specified string is reversed.

Syntax

StrReverse(expression)

Parameters

expression: Required. String expression whose characters are to be reversed. If expression is a zero-length string (""), a zero-length string is returned.

Returns

Returns a String with the characters in reverse order.

Remarks

The StrReverse function reverses the order of characters in a string:

Character-by-character reversal: Reverses individual characters, not words
Unicode support: Works correctly with Unicode characters
Empty string handling: Returns empty string if input is empty
Null handling: Returns Null if expression is Null
Preserves spaces: Spaces are treated like any other character and reversed
Case preserved: Original case of characters is maintained
Single pass: Efficient single-pass algorithm
VB6/VBA only: Available in VB6 and VBA, not in VBScript

Common Use Cases

Reversing strings for display or analysis
Palindrome checking (compare string with its reverse)
Text transformations and puzzles
Data obfuscation (simple, not secure)
Mirror text effects
String manipulation algorithms

Comparison with Manual Reversal

StrReverse is more efficient than manually reversing with loops:

' Using StrReverse (preferred)
reversed = StrReverse(original)

' Manual reversal (slower)
For i = Len(original) To 1 Step -1
reversed = reversed & Mid$(original, i, 1)
Next i

Typical Uses

Palindrome Detection: Check if a string reads the same forwards and backwards
Text Effects: Create mirror or reversed text displays
String Analysis: Analyze patterns in reversed strings
Data Transformation: Transform data for specific algorithms
Puzzles and Games: Implement word games and puzzles
File Processing: Process files that store data in reverse order
Encoding: Simple (non-cryptographic) string obfuscation
Testing: Generate test data with predictable patterns

Basic Examples

Example 1: Basic String Reversal

Dim original As String
Dim reversed As String

original = "Hello"
reversed = StrReverse(original)  ' "olleH"

original = "VB6"
reversed = StrReverse(original)  ' "6BV"

original = "12345"
reversed = StrReverse(original)  ' "54321"

Example 2: Palindrome Check

Function IsPalindrome(text As String) As Boolean
Dim normalized As String

' Remove spaces and convert to lowercase for comparison
normalized = Replace(LCase$(text), " ", "")

' Compare with reversed version
IsPalindrome = (normalized = StrReverse(normalized))
End Function

' Examples:
' IsPalindrome("racecar") = True
' IsPalindrome("A man a plan a canal Panama") = True (after normalization)
' IsPalindrome("hello") = False

Example 3: Reverse Words in Sentence

Function ReverseWords(sentence As String) As String
Dim words() As String
Dim i As Integer
Dim result As String

words = Split(sentence, " ")

result = ""
For i = UBound(words) To LBound(words) Step -1
If i < UBound(words) Then result = result & " "
result = result & words(i)
Next i

ReverseWords = result
End Function

' Example: "Hello World" becomes "World Hello"

Example 4: Simple Obfuscation

Function ObfuscateString(text As String) As String
' Simple, non-secure obfuscation
ObfuscateString = StrReverse(text)
End Function

Function DeobfuscateString(text As String) As String
' Reverse the obfuscation
DeobfuscateString = StrReverse(text)
End Function

Common Patterns

Pattern 1: Check Palindrome (Case-Insensitive)

Function IsPalindromeIgnoreCase(text As String) As Boolean
Dim lower As String
lower = LCase$(text)
IsPalindromeIgnoreCase = (lower = StrReverse(lower))
End Function

Pattern 2: Reverse Each Word

Function ReverseEachWord(sentence As String) As String
Dim words() As String
Dim i As Integer

words = Split(sentence, " ")
For i = LBound(words) To UBound(words)
words(i) = StrReverse(words(i))
Next i

ReverseEachWord = Join(words, " ")
End Function

Pattern 3: Get Last N Characters Efficiently

Function GetLastNChars(text As String, n As Integer) As String
Dim reversed As String
reversed = StrReverse(text)
GetLastNChars = StrReverse(Left$(reversed, n))
End Function

Pattern 4: Check If Strings Are Reverses

Function AreReverses(str1 As String, str2 As String) As Boolean
AreReverses = (str1 = StrReverse(str2))
End Function

Pattern 5: Reverse File Extension

Function ReverseExtension(filename As String) As String
Dim dotPos As Integer
Dim name As String
Dim ext As String

dotPos = InStrRev(filename, ".")
If dotPos > 0 Then
name = Left$(filename, dotPos - 1)
ext = Mid$(filename, dotPos + 1)
ReverseExtension = name & "." & StrReverse(ext)
Else
ReverseExtension = filename
End If
End Function

Pattern 6: Mirror Text Display

Function CreateMirrorText(text As String) As String
CreateMirrorText = text & " | " & StrReverse(text)
End Function

Pattern 7: Reverse and Uppercase

Function ReverseAndUpper(text As String) As String
ReverseAndUpper = UCase$(StrReverse(text))
End Function

Pattern 8: Find Reverse Match in Array

Function FindReverseMatch(arr() As String, searchValue As String) As Integer
Dim i As Integer
Dim reversed As String

reversed = StrReverse(searchValue)

For i = LBound(arr) To UBound(arr)
If arr(i) = reversed Then
FindReverseMatch = i
Exit Function
End If
Next i

FindReverseMatch = -1
End Function

Pattern 9: Reverse Between Delimiters

Function ReverseBetween(text As String, startDelim As String, endDelim As String) As String
Dim startPos As Integer
Dim endPos As Integer
Dim middle As String

startPos = InStr(text, startDelim)
endPos = InStr(startPos + Len(startDelim), text, endDelim)

If startPos > 0 And endPos > startPos Then
middle = Mid$(text, startPos + Len(startDelim), endPos - startPos - Len(startDelim))
ReverseBetween = Left$(text, startPos + Len(startDelim) - 1) & _
StrReverse(middle) & _
Mid$(text, endPos)
Else
ReverseBetween = text
End If
End Function

Pattern 10: Alternate Characters Reversed

Function AlternateReverse(text As String) As String
Dim i As Integer
Dim result As String
Dim reversed As String

reversed = StrReverse(text)
result = ""

For i = 1 To Len(text)
If i Mod 2 = 1 Then
result = result & Mid$(text, i, 1)
Else
result = result & Mid$(reversed, i, 1)
End If
Next i

AlternateReverse = result
End Function

Advanced Usage

Example 1: Palindrome Checker Class

' Class: PalindromeChecker
' Checks various types of palindromes
Option Explicit

Private m_IgnoreCase As Boolean
Private m_IgnoreSpaces As Boolean
Private m_IgnorePunctuation As Boolean

Public Sub Initialize(Optional ignoreCase As Boolean = True, _
Optional ignoreSpaces As Boolean = True, _
Optional ignorePunctuation As Boolean = False)
m_IgnoreCase = ignoreCase
m_IgnoreSpaces = ignoreSpaces
m_IgnorePunctuation = ignorePunctuation
End Sub

Public Function IsPalindrome(text As String) As Boolean
Dim normalized As String
normalized = NormalizeText(text)
IsPalindrome = (normalized = StrReverse(normalized))
End Function

Public Function GetLongestPalindromeSubstring(text As String) As String
Dim i As Integer
Dim j As Integer
Dim substring As String
Dim longest As String

longest = ""

For i = 1 To Len(text)
For j = i To Len(text)
substring = Mid$(text, i, j - i + 1)
If IsPalindrome(substring) And Len(substring) > Len(longest) Then
longest = substring
End If
Next j
Next i

GetLongestPalindromeSubstring = longest
End Function

Private Function NormalizeText(text As String) As String
Dim result As String
result = text

If m_IgnoreCase Then
result = LCase$(result)
End If

If m_IgnoreSpaces Then
result = Replace(result, " ", "")
End If

If m_IgnorePunctuation Then
result = RemovePunctuation(result)
End If

NormalizeText = result
End Function

Private Function RemovePunctuation(text As String) As String
Dim i As Integer
Dim char As String
Dim result As String

result = ""
For i = 1 To Len(text)
char = Mid$(text, i, 1)
If (char >= "A" And char <= "Z") Or (char >= "a" And char <= "z") Or _
(char >= "0" And char <= "9") Then
result = result & char
End If
Next i

RemovePunctuation = result
End Function

Example 2: String Reversal Utilities

' Module: StringReversalUtils
' Utilities for reversing strings in various ways
Option Explicit

Public Function ReverseString(text As String) As String
ReverseString = StrReverse(text)
End Function

Public Function ReverseWords(sentence As String) As String
Dim words() As String
Dim i As Integer
Dim result As String

words = Split(sentence, " ")
result = ""

For i = UBound(words) To LBound(words) Step -1
If Len(result) > 0 Then result = result & " "
result = result & words(i)
Next i

ReverseWords = result
End Function

Public Function ReverseEachWord(sentence As String) As String
Dim words() As String
Dim i As Integer

words = Split(sentence, " ")
For i = LBound(words) To UBound(words)
words(i) = StrReverse(words(i))
Next i

ReverseEachWord = Join(words, " ")
End Function

Public Function ReverseLines(text As String) As String
Dim lines() As String
Dim i As Integer
Dim result As String

lines = Split(text, vbCrLf)
result = ""

For i = UBound(lines) To LBound(lines) Step -1
If Len(result) > 0 Then result = result & vbCrLf
result = result & lines(i)
Next i

ReverseLines = result
End Function

Public Function ReverseArray(arr() As String) As String()
Dim result() As String
Dim i As Integer
Dim j As Integer

ReDim result(LBound(arr) To UBound(arr))
j = LBound(arr)

For i = UBound(arr) To LBound(arr) Step -1
result(j) = arr(i)
j = j + 1
Next i

ReverseArray = result
End Function

Example 3: Text Transformer Class

' Class: TextTransformer
' Performs various text transformations including reversal
Option Explicit

Public Function Transform(text As String, transformType As String) As String
Select Case UCase$(transformType)
Case "REVERSE"
Transform = StrReverse(text)
Case "REVERSE_WORDS"
Transform = ReverseWords(text)
Case "REVERSE_EACH_WORD"
Transform = ReverseEachWord(text)
Case "MIRROR"
Transform = text & " " & StrReverse(text)
Case "PALINDROME"
Transform = text & StrReverse(text)
Case Else
Transform = text
End Select
End Function

Private Function ReverseWords(sentence As String) As String
Dim words() As String
Dim i As Integer
Dim result As String

words = Split(sentence, " ")
result = ""

For i = UBound(words) To LBound(words) Step -1
If Len(result) > 0 Then result = result & " "
result = result & words(i)
Next i

ReverseWords = result
End Function

Private Function ReverseEachWord(sentence As String) As String
Dim words() As String
Dim i As Integer

words = Split(sentence, " ")
For i = LBound(words) To UBound(words)
words(i) = StrReverse(words(i))
Next i

ReverseEachWord = Join(words, " ")
End Function

Public Function CreatePalindrome(text As String) As String
CreatePalindrome = text & StrReverse(text)
End Function

Public Function IsPalindrome(text As String) As Boolean
IsPalindrome = (text = StrReverse(text))
End Function

Example 4: String Analyzer Module

' Module: StringAnalyzer
' Analyzes strings using reversal techniques
Option Explicit

Public Function ContainsPalindrome(text As String, minLength As Integer) As Boolean
Dim i As Integer
Dim j As Integer
Dim substring As String

For i = 1 To Len(text) - minLength + 1
For j = minLength To Len(text) - i + 1
substring = Mid$(text, i, j)
If substring = StrReverse(substring) Then
ContainsPalindrome = True
Exit Function
End If
Next j
Next i

ContainsPalindrome = False
End Function

Public Function FindAllPalindromes(text As String, minLength As Integer) As Collection
Dim palindromes As New Collection
Dim i As Integer
Dim j As Integer
Dim substring As String

For i = 1 To Len(text)
For j = minLength To Len(text) - i + 1
substring = Mid$(text, i, j)
If substring = StrReverse(substring) Then
On Error Resume Next
palindromes.Add substring, substring
On Error GoTo 0
End If
Next j
Next i

Set FindAllPalindromes = palindromes
End Function

Public Function GetSymmetryScore(text As String) As Double
' Calculate how symmetric a string is (0-100%)
Dim matches As Integer
Dim i As Integer
Dim len As Integer

len = Len(text)
If len = 0 Then
GetSymmetryScore = 0
Exit Function
End If

matches = 0
For i = 1 To len \ 2
If Mid$(text, i, 1) = Mid$(text, len - i + 1, 1) Then
matches = matches + 1
End If
Next i

GetSymmetryScore = (matches / (len \ 2)) * 100
End Function

Public Function IsAnagram(str1 As String, str2 As String) As Boolean
' Not directly using StrReverse, but useful utility
Dim sorted1 As String
Dim sorted2 As String

sorted1 = SortString(LCase$(str1))
sorted2 = SortString(LCase$(str2))

IsAnagram = (sorted1 = sorted2)
End Function

Private Function SortString(text As String) As String
' Simple bubble sort for demonstration
Dim chars() As String
Dim i As Integer
Dim j As Integer
Dim temp As String

ReDim chars(1 To Len(text))
For i = 1 To Len(text)
chars(i) = Mid$(text, i, 1)
Next i

For i = 1 To UBound(chars) - 1
For j = i + 1 To UBound(chars)
If chars(i) > chars(j) Then
temp = chars(i)
chars(i) = chars(j)
chars(j) = temp
End If
Next j
Next i

SortString = Join(chars, "")
End Function

Error Handling

The StrReverse function typically does not raise errors under normal circumstances:

Returns empty string if input is empty string
Returns Null if input is Null (not an error)
Error 13 (Type mismatch): If expression cannot be converted to a string

Performance Notes

Very fast and efficient (optimized native function)
Much faster than manual character-by-character reversal in VB6
Performance is O(n) where n is string length
No significant overhead for typical string lengths
For very large strings (megabytes), consider memory constraints

Best Practices

Use StrReverse instead of manual loops for reversing strings (faster and cleaner)
Handle Null values explicitly when working with Variant types
Normalize before palindrome checks (remove spaces, convert case)
Don't use for security - StrReverse is not encryption, only obfuscation
Cache reversed strings if used multiple times in comparisons
Combine with other functions like LCase$, Trim$ for text processing
Test edge cases like empty strings and single-character strings
Document intent when using StrReverse in non-obvious ways
Consider alternatives for word-level reversal (Split/Join approach)
Use for validation like palindrome checking or symmetry analysis

Comparison Table

Approach	Code	Speed	Clarity
`StrReverse`	`StrReverse(s)`	Fast	Excellent
Manual loop	`For i = Len(s) To 1 Step -1...`	Slow	Poor
Recursion	`ReverseRecursive(s)`	Very slow	Poor

Platform Notes

Available in VB6 and VBA
Not available in VBScript (must implement manually)
Works correctly with Unicode characters
Behavior consistent across VB6 and VBA
No locale-specific behavior

Limitations

Cannot reverse only part of a string (use Mid$ to extract first)
Cannot reverse words rather than characters (use Split/Join)
Not available in VBScript
Returns Null for Null input (may be unexpected)
No option to reverse specific character ranges
Cannot specify custom reversal rules