ubound - Arrays - VB6Parse Library Reference

VB6 UBound Function

The UBound function returns a Long containing the largest available subscript for the indicated dimension of an array.

Syntax

UBound(arrayname[, dimension])

Parameters

arrayname: Required. Name of the array variable. Follows standard Visual Basic naming conventions.
dimension: Optional. Variant (Long). Specifies which dimension's upper bound is returned. Use 1 for the first dimension, 2 for the second, and so on. If dimension is omitted, 1 is assumed.

Returns

Returns a Long containing the largest available subscript for the specified dimension of the array.

Remarks

The UBound function is used to determine the upper limit of an array dimension:

Dimension parameter: If omitted, defaults to 1 (first dimension)
Multi-dimensional arrays: Use dimension parameter to specify which dimension
Zero-based arrays: UBound returns the upper index regardless of lower bound
Paired with LBound: Use LBound to get the lower bound
Array size calculation: Size = UBound - LBound + 1
Dynamic arrays: Returns current upper bound (changes with ReDim)
Fixed arrays: Returns the declared upper bound
Error on uninitialized: Error 9 (Subscript out of range) if array not initialized
ParamArray: Works with ParamArray arguments to find number of elements

Common Array Declarations

Dim arr(5)              ' LBound = 0, UBound = 5 (6 elements)
Dim arr(1 To 5)         ' LBound = 1, UBound = 5 (5 elements)
Dim arr(10 To 20)       ' LBound = 10, UBound = 20 (11 elements)
Dim arr(5, 3)           ' First: 0-5, Second: 0-3
Dim arr(1 To 5, 1 To 3) ' First: 1-5, Second: 1-3

Option Base Impact

The Option Base statement affects default lower bounds: - Option Base 0: Default lower bound is 0 (default) - Option Base 1: Default lower bound is 1 - Explicit bounds (e.g., 1 To 5) override Option Base

Dynamic Arrays

For dynamic arrays: - Before ReDim: Error 9 if accessed - After ReDim: Returns current upper bound - ReDim Preserve: Can change upper bound while preserving data - Erase: Makes array uninitialized again

Typical Uses

Loop Bounds: Iterate through all array elements
Array Size: Calculate the number of elements in an array
Validation: Check if an index is within valid range
Dynamic Resizing: Determine current size before ReDim
ParamArray: Count variable number of arguments
Array Copying: Determine target array size
Search Operations: Set loop limits for array searches
Multi-dimensional: Navigate complex array structures

Basic Examples

Example 1: Simple Array Iteration

Dim values(10) As Integer
Dim i As Integer

For i = LBound(values) To UBound(values)
values(i) = i * 2
Next i

Example 2: Calculate Array Size

Function GetArraySize(arr() As Variant) As Long
GetArraySize = UBound(arr) - LBound(arr) + 1
End Function

' Usage:
Dim myArray(5 To 15) As String
Debug.Print GetArraySize(myArray) ' Prints: 11

Example 3: Multi-Dimensional Array

Sub ProcessMatrix()
Dim matrix(1 To 3, 1 To 4) As Double
Dim row As Integer
Dim col As Integer

For row = LBound(matrix, 1) To UBound(matrix, 1)
For col = LBound(matrix, 2) To UBound(matrix, 2)
matrix(row, col) = row * col
Next col
Next row
End Sub

Example 4: `ParamArray` with `UBound`

Function Sum(ParamArray values() As Variant) As Double
Dim i As Integer
Dim total As Double

total = 0
For i = LBound(values) To UBound(values)
total = total + values(i)
Next i

Sum = total
End Function

' Usage: result = Sum(1, 2, 3, 4, 5)

Common Patterns

Pattern 1: Safe Array Iteration

Sub IterateArray(arr() As Variant)
Dim i As Long

For i = LBound(arr) To UBound(arr)
Debug.Print arr(i)
Next i
End Sub

Pattern 2: Check If Array Is Empty

Function IsArrayEmpty(arr() As Variant) As Boolean
On Error Resume Next
IsArrayEmpty = (UBound(arr) < LBound(arr))
If Err.Number <> 0 Then IsArrayEmpty = True
End Function

Pattern 3: Resize Array with Data Preservation

Sub AddArrayElement(arr() As Variant, newValue As Variant)
Dim newSize As Long

On Error Resume Next
newSize = UBound(arr) + 1
If Err.Number <> 0 Then
' Array not initialized
ReDim arr(0 To 0)
newSize = 0
Else
ReDim Preserve arr(LBound(arr) To newSize)
End If

arr(newSize) = newValue
End Sub

Pattern 4: Count Elements in `ParamArray`

Function CountArgs(ParamArray args() As Variant) As Long
On Error Resume Next
CountArgs = UBound(args) - LBound(args) + 1
If Err.Number <> 0 Then CountArgs = 0
End Function

Pattern 5: Validate Array Index

Function IsValidIndex(arr() As Variant, index As Long) As Boolean
On Error Resume Next
IsValidIndex = (index >= LBound(arr) And index <= UBound(arr))
If Err.Number <> 0 Then IsValidIndex = False
End Function

Pattern 6: Copy Array

Function CopyArray(source() As Variant) As Variant()
Dim dest() As Variant
Dim i As Long

ReDim dest(LBound(source) To UBound(source))

For i = LBound(source) To UBound(source)
dest(i) = source(i)
Next i

CopyArray = dest
End Function

Pattern 7: Reverse Array

Sub ReverseArray(arr() As Variant)
Dim i As Long
Dim j As Long
Dim temp As Variant

i = LBound(arr)
j = UBound(arr)

While i < j
temp = arr(i)
arr(i) = arr(j)
arr(j) = temp
i = i + 1
j = j - 1
Wend
End Sub

Pattern 8: Find Last Element

Function GetLastElement(arr() As Variant) As Variant
GetLastElement = arr(UBound(arr))
End Function

Pattern 9: Remove Last Element

Sub RemoveLastElement(arr() As Variant)
Dim newUpper As Long

newUpper = UBound(arr) - 1
If newUpper >= LBound(arr) Then
ReDim Preserve arr(LBound(arr) To newUpper)
End If
End Sub

Pattern 10: Multi-Dimensional Size

Function GetArrayDimensions(arr As Variant) As Integer
Dim dimension As Integer

On Error Resume Next
dimension = 1
Do While Err.Number = 0
Dim test As Long
test = UBound(arr, dimension)
dimension = dimension + 1
Loop

GetArrayDimensions = dimension - 1
End Function

Advanced Usage

Example 1: Dynamic Array Manager Class

' Class: DynamicArrayManager
' Manages a dynamic array with automatic resizing
Option Explicit

Private m_Data() As Variant
Private m_Initialized As Boolean

Public Sub Initialize(Optional initialSize As Long = 10)
ReDim m_Data(0 To initialSize - 1)
m_Initialized = True
End Sub

Public Sub Add(value As Variant)
Dim newIndex As Long

If Not m_Initialized Then
Initialize
newIndex = 0
Else
newIndex = UBound(m_Data) + 1
ReDim Preserve m_Data(0 To newIndex)
End If

m_Data(newIndex) = value
End Sub

Public Function GetItem(index As Long) As Variant
If index < LBound(m_Data) Or index > UBound(m_Data) Then
Err.Raise 9, , "Index out of range"
End If

If IsObject(m_Data(index)) Then
Set GetItem = m_Data(index)
Else
GetItem = m_Data(index)
End If
End Function

Public Sub SetItem(index As Long, value As Variant)
If index < LBound(m_Data) Or index > UBound(m_Data) Then
Err.Raise 9, , "Index out of range"
End If

m_Data(index) = value
End Sub

Public Function Count() As Long
If Not m_Initialized Then
Count = 0
Else
Count = UBound(m_Data) - LBound(m_Data) + 1
End If
End Function

Public Sub Clear()
If m_Initialized Then
Erase m_Data
m_Initialized = False
End If
End Sub

Public Function ToArray() As Variant()
ToArray = m_Data
End Function

Example 2: Array Utilities Module

' Module: ArrayUtilities
' Comprehensive array manipulation utilities
Option Explicit

Public Function ArraySize(arr As Variant) As Long
On Error Resume Next
ArraySize = UBound(arr) - LBound(arr) + 1
If Err.Number <> 0 Then ArraySize = 0
End Function

Public Function ArrayContains(arr() As Variant, value As Variant) As Boolean
Dim i As Long

ArrayContains = False
For i = LBound(arr) To UBound(arr)
If arr(i) = value Then
ArrayContains = True
Exit Function
End If
Next i
End Function

Public Function ArrayIndexOf(arr() As Variant, value As Variant) As Long
Dim i As Long

ArrayIndexOf = -1
For i = LBound(arr) To UBound(arr)
If arr(i) = value Then
ArrayIndexOf = i
Exit Function
End If
Next i
End Function

Public Sub ArraySort(arr() As Variant)
Dim i As Long
Dim j As Long
Dim temp As Variant

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

Public Function ArrayFilter(arr() As Variant, filterValue As Variant) As Variant()
Dim result() As Variant
Dim i As Long
Dim count As Long

count = 0
For i = LBound(arr) To UBound(arr)
If arr(i) <> filterValue Then
ReDim Preserve result(0 To count)
result(count) = arr(i)
count = count + 1
End If
Next i

ArrayFilter = result
End Function

Public Function ArraySlice(arr() As Variant, startIndex As Long, _
endIndex As Long) As Variant()
Dim result() As Variant
Dim i As Long
Dim idx As Long

ReDim result(0 To endIndex - startIndex)

idx = 0
For i = startIndex To endIndex
result(idx) = arr(i)
idx = idx + 1
Next i

ArraySlice = result
End Function

Example 3: Matrix Operations Class

' Class: MatrixOperations
' Performs operations on 2D arrays
Option Explicit

Public Function GetRowCount(matrix As Variant) As Long
On Error Resume Next
GetRowCount = UBound(matrix, 1) - LBound(matrix, 1) + 1
If Err.Number <> 0 Then GetRowCount = 0
End Function

Public Function GetColumnCount(matrix As Variant) As Long
On Error Resume Next
GetColumnCount = UBound(matrix, 2) - LBound(matrix, 2) + 1
If Err.Number <> 0 Then GetColumnCount = 0
End Function

Public Function GetRow(matrix As Variant, rowIndex As Long) As Variant()
Dim result() As Variant
Dim col As Long
Dim idx As Long

ReDim result(LBound(matrix, 2) To UBound(matrix, 2))

For col = LBound(matrix, 2) To UBound(matrix, 2)
result(col) = matrix(rowIndex, col)
Next col

GetRow = result
End Function

Public Function GetColumn(matrix As Variant, colIndex As Long) As Variant()
Dim result() As Variant
Dim row As Long

ReDim result(LBound(matrix, 1) To UBound(matrix, 1))

For row = LBound(matrix, 1) To UBound(matrix, 1)
result(row) = matrix(row, colIndex)
Next row

GetColumn = result
End Function

Public Function TransposeMatrix(matrix As Variant) As Variant
Dim result() As Variant
Dim row As Long
Dim col As Long

ReDim result(LBound(matrix, 2) To UBound(matrix, 2), _
LBound(matrix, 1) To UBound(matrix, 1))

For row = LBound(matrix, 1) To UBound(matrix, 1)
For col = LBound(matrix, 2) To UBound(matrix, 2)
result(col, row) = matrix(row, col)
Next col
Next row

TransposeMatrix = result
End Function

Example 4: Collection to Array Converter

' Module: CollectionConverter
' Converts between Collections and Arrays
Option Explicit

Public Function CollectionToArray(col As Collection) As Variant()
Dim result() As Variant
Dim i As Long

If col.Count = 0 Then
CollectionToArray = Array()
Exit Function
End If

ReDim result(1 To col.Count)

For i = 1 To col.Count
If IsObject(col(i)) Then
Set result(i) = col(i)
Else
result(i) = col(i)
End If
Next i

CollectionToArray = result
End Function

Public Function ArrayToCollection(arr() As Variant) As Collection
Dim result As New Collection
Dim i As Long

For i = LBound(arr) To UBound(arr)
result.Add arr(i)
Next i

Set ArrayToCollection = result
End Function

Public Function MergeArrays(ParamArray arrays() As Variant) As Variant()
Dim result() As Variant
Dim totalSize As Long
Dim currentIndex As Long
Dim i As Long
Dim j As Long
Dim arr As Variant

' Calculate total size
totalSize = 0
For i = LBound(arrays) To UBound(arrays)
arr = arrays(i)
totalSize = totalSize + (UBound(arr) - LBound(arr) + 1)
Next i

' Merge arrays
ReDim result(0 To totalSize - 1)
currentIndex = 0

For i = LBound(arrays) To UBound(arrays)
arr = arrays(i)
For j = LBound(arr) To UBound(arr)
result(currentIndex) = arr(j)
currentIndex = currentIndex + 1
Next j
Next i

MergeArrays = result
End Function

Error Handling

The UBound function can raise the following errors:

Error 9 (Subscript out of range): If the array has not been initialized (for dynamic arrays)
Error 9 (Subscript out of range): If dimension is less than 1 or greater than the array's number of dimensions
Error 13 (Type mismatch): If the variable is not an array
Error 5 (Invalid procedure call or argument): If dimension parameter is invalid

Performance Notes

Very fast O(1) operation - directly returns array metadata
No performance difference between dimensions
Safe to call repeatedly in loops
Consider caching value if used extensively in tight loops
No memory allocation or copying involved

Best Practices

Always use with LBound for complete array bounds information
Check for initialization with On Error Resume Next for dynamic arrays
Use in For loops instead of hardcoding array sizes
Specify dimension explicitly for multi-dimensional arrays
Cache in variables if used multiple times in tight loops
Validate dimension parameter when working with multi-dimensional arrays
Handle errors gracefully for potentially uninitialized arrays
Use for ParamArray to handle variable arguments
Document array bounds in function comments
Prefer explicit bounds in array declarations for clarity

Comparison Table

Function	Purpose	Returns	Notes
`UBound`	Upper bound	Long	Largest valid index
`LBound`	Lower bound	Long	Smallest valid index
`Array`	Create array	Variant	Returns zero-based array
`ReDim`	Resize array	N/A	Statement, not function

Platform Notes

Available in VB6, VBA, and VBScript
Behavior consistent across platforms
Returns Long (32-bit signed integer)
Maximum array size limited by available memory
Multi-dimensional arrays limited to 60 dimensions

Limitations

Cannot determine if array is initialized without error handling
Does not return array capacity (allocated size vs. used size)
No built-in way to get all dimensions at once
Dimension parameter must be compile-time constant in some contexts
Cannot be used on Collections or other non-array types
Does not work with jagged arrays (arrays of arrays) directly