`AscB` Function

Returns an Integer representing the byte value (ANSI code) of the first byte in a string. The "B" suffix indicates this is the byte (ANSI) version of the Asc function.

Syntax

AscB(string)

Parameters

string: Required. Any valid string expression. If the string contains no characters, a runtime error occurs (Error 5: Invalid procedure call or argument).

Returns

Returns an Integer (0-255) representing the byte value of the first byte in the string.

Remarks

AscB returns the ANSI byte value of the first byte in a string, not the character code.
The B suffix stands for "Byte", distinguishing it from the Unicode AscW function.
For single-byte character sets (ANSI), AscB and Asc return the same value.
For multi-byte character sets (like DBCS), AscB returns only the first byte of a multi-byte character.
The return value is always in the range 0-255.
If the string is empty (""), a runtime error occurs (Error 5).
AscB is useful for low-level byte operations and working with binary data.
The inverse function is ChrB, which converts a byte value back to a character.
For Unicode code points, use AscW instead of AscB.

Typical Uses

Byte-level text analysis - Examine individual bytes in ANSI strings
Binary data processing - Extract byte values from binary strings
File format parsing - Read byte values from file headers or data structures
Legacy protocol support - Work with protocols that use ANSI byte values
Character encoding detection - Analyze byte patterns in text
Checksum calculations - Use byte values for checksums or hash calculations
Low-level string comparison - Compare strings at the byte level

Basic Examples

' Example 1: Simple byte value
Dim byteVal As Integer
byteVal = AscB("A")  ' Returns 65

' Example 2: Extended ANSI character
Dim code As Integer
code = AscB("é")  ' Returns 233 (in Windows-1252 code page)

' Example 3: First byte of multi-byte character
' In DBCS (Double Byte Character Set) systems
Dim firstByte As Integer
firstByte = AscB("中")  ' Returns first byte only (varies by encoding)

' Example 4: Control character
Dim tabByte As Integer
tabByte = AscB(vbTab)  ' Returns 9

Common Patterns

Validate ASCII Range

Function IsASCII(char As String) As Boolean
If Len(char) = 0 Then Exit Function
IsASCII = (AscB(char) < 128)
End Function

Check for Control Characters

Function IsControlChar(char As String) As Boolean
If Len(char) = 0 Then Exit Function
Dim byteVal As Integer
byteVal = AscB(char)
IsControlChar = (byteVal < 32 Or byteVal = 127)
End Function

Compare Byte Values

Function CompareBytes(str1 As String, str2 As String) As Integer
If Len(str1) = 0 Or Len(str2) = 0 Then Exit Function
CompareBytes = AscB(str1) - AscB(str2)
End Function

Extract Byte Array

Function GetByteArray(text As String) As Variant
Dim bytes() As Integer
Dim i As Long

If Len(text) = 0 Then Exit Function

ReDim bytes(1 To Len(text))
For i = 1 To Len(text)
bytes(i) = AscB(Mid(text, i, 1))
Next i

GetByteArray = bytes
End Function

Calculate Simple Checksum

Function SimpleChecksum(text As String) As Long
Dim i As Long
Dim checksum As Long

For i = 1 To Len(text)
checksum = checksum + AscB(Mid(text, i, 1))
Next i

SimpleChecksum = checksum Mod 256
End Function

Detect Line Endings

Function DetectLineEnding(text As String) As String
Dim i As Long
Dim byteVal As Integer

For i = 1 To Len(text)
byteVal = AscB(Mid(text, i, 1))
If byteVal = 13 Then  ' CR
If i < Len(text) And AscB(Mid(text, i + 1, 1)) = 10 Then
DetectLineEnding = "CRLF"
Else
DetectLineEnding = "CR"
End If
Exit Function
ElseIf byteVal = 10 Then  ' LF
DetectLineEnding = "LF"
Exit Function
End If
Next i
End Function

Hex Dump Generator

Function ByteToHex(char As String) As String
If Len(char) = 0 Then Exit Function
Dim byteVal As Integer
byteVal = AscB(char)
ByteToHex = Right("0" & Hex(byteVal), 2)
End Function

Case-Insensitive Byte Compare

Function ByteEqualsIgnoreCase(char1 As String, char2 As String) As Boolean
If Len(char1) = 0 Or Len(char2) = 0 Then Exit Function

Dim byte1 As Integer, byte2 As Integer
byte1 = AscB(char1)
byte2 = AscB(char2)

' Convert uppercase to lowercase (65-90 to 97-122)
If byte1 >= 65 And byte1 <= 90 Then byte1 = byte1 + 32
If byte2 >= 65 And byte2 <= 90 Then byte2 = byte2 + 32

ByteEqualsIgnoreCase = (byte1 = byte2)
End Function

Filter Printable Characters

Function FilterPrintable(text As String) As String
Dim result As String
Dim i As Long
Dim byteVal As Integer

For i = 1 To Len(text)
byteVal = AscB(Mid(text, i, 1))
If byteVal >= 32 And byteVal <= 126 Then
result = result & Mid(text, i, 1)
End If
Next i

FilterPrintable = result
End Function

Encode for URL

Function NeedsURLEncoding(char As String) As Boolean
If Len(char) = 0 Then Exit Function

Dim byteVal As Integer
byteVal = AscB(char)

' Check if character needs encoding
If (byteVal >= 48 And byteVal <= 57) Or _
(byteVal >= 65 And byteVal <= 90) Or _
(byteVal >= 97 And byteVal <= 122) Then
NeedsURLEncoding = False
Else
NeedsURLEncoding = True
End If
End Function

Advanced Examples

Binary Data Parser

Function ParseBinaryHeader(data As String) As Variant
' Parse a binary file header (example: BMP format)
Dim header As Variant
ReDim header(1 To 4)

If Len(data) < 4 Then Exit Function

' Read signature bytes
header(1) = AscB(Mid(data, 1, 1))  ' 'B' = 66
header(2) = AscB(Mid(data, 2, 1))  ' 'M' = 77

' Read size bytes (little-endian)
header(3) = AscB(Mid(data, 3, 1))
header(4) = AscB(Mid(data, 4, 1))

ParseBinaryHeader = header
End Function

XOR Encryption/Decryption

Function XOREncrypt(text As String, key As String) As String
Dim result As String
Dim i As Long, keyPos As Long
Dim textByte As Integer, keyByte As Integer

If Len(text) = 0 Or Len(key) = 0 Then Exit Function

keyPos = 1
For i = 1 To Len(text)
textByte = AscB(Mid(text, i, 1))
keyByte = AscB(Mid(key, keyPos, 1))

result = result & ChrB(textByte Xor keyByte)

keyPos = keyPos + 1
If keyPos > Len(key) Then keyPos = 1
Next i

XOREncrypt = result
End Function

CSV Field Parser with Byte Analysis

Function ParseCSVField(field As String) As String
Dim result As String
Dim i As Long
Dim byteVal As Integer
Dim inQuotes As Boolean

For i = 1 To Len(field)
byteVal = AscB(Mid(field, i, 1))

Select Case byteVal
Case 34  ' Double quote
inQuotes = Not inQuotes
Case 44  ' Comma
If Not inQuotes Then Exit Function
result = result & Chr(byteVal)
Case Else
result = result & Chr(byteVal)
End Select
Next i

ParseCSVField = result
End Function

Character Set Validator

Function ValidateCharacterSet(text As String, validSet As String) As Boolean
Dim i As Long, j As Long
Dim textByte As Integer
Dim found As Boolean

For i = 1 To Len(text)
textByte = AscB(Mid(text, i, 1))
found = False

For j = 1 To Len(validSet)
If textByte = AscB(Mid(validSet, j, 1)) Then
found = True
Exit For
End If
Next j

If Not found Then
ValidateCharacterSet = False
Exit Function
End If
Next i

ValidateCharacterSet = True
End Function

Error Handling

Function SafeAscB(text As String) As Integer
On Error GoTo ErrorHandler

If Len(text) = 0 Then
SafeAscB = -1  ' Error indicator
Exit Function
End If

SafeAscB = AscB(text)
Exit Function

ErrorHandler:
SafeAscB = -1
End Function

Performance Notes

AscB is a very fast operation with minimal overhead
When processing long strings byte-by-byte, consider using Mid function efficiently
For repeated byte extraction, the performance is generally good
Avoid calling AscB in tight loops if the value can be cached
AscB is faster than string comparison for byte-level operations

Best Practices

Validate input - Always check for empty strings before calling AscB
Use for byte operations - Prefer AscB over Asc when working with binary data
Handle errors - Wrap AscB calls in error handlers when processing untrusted input
Document byte values - Use constants or comments to explain non-obvious byte values
Consider encoding - Be aware of system code page when working with extended ANSI
Use with ChrB - Pair with ChrB for byte-to-character conversions
Test edge cases - Verify behavior with empty strings, control characters, and extended ANSI

Function	Returns	Character Set	Use Case
`Asc`	Integer (0-255 or Unicode)	System default	General character codes
`AscB`	Integer (0-255)	ANSI byte value	Byte-level operations
`AscW`	Integer (0-65535)	Unicode code point	International text
`ChrB`	String (ANSI)	ANSI (inverse)	Convert byte to character

Common Byte Values Reference

Some commonly used byte values with AscB:

0: Null character (NUL)
9: Tab (HT)
10: Line feed (LF)
13: Carriage return (CR)
32: Space
48-57: Digits '0'-'9'
65-90: Uppercase letters 'A'-'Z'
97-122: Lowercase letters 'a'-'z'
127: Delete (DEL)
128-255: Extended ANSI (varies by code page)

Platform Notes

On Windows systems, AscB uses the system's ANSI code page (e.g., Windows-1252)
Different code pages may interpret bytes 128-255 differently
For portable code, stick to ASCII range (0-127) when possible
On older systems (Windows 95/98/ME), ANSI encoding is the native string format
On modern Windows (NT-based), strings are Unicode internally but AscB still returns ANSI bytes

Limitations

Returns only the first byte, not the full character in multi-byte encodings
Cannot handle Unicode characters outside the ANSI range (0-255) properly
Runtime error occurs with empty strings
Code page dependent for extended ANSI characters (128-255)
Not suitable for Unicode text processing (use AscW instead)

AscB Function