Implementing String.Format() in VB6

Question

Can String.Format() be implemented in VB6, at least a close-enough version of it that could be useful when programming in good ol' VB6?

Good resource on the matter of VB6 string manipulation performance: http://www.aivosto.com/vbtips/stringopt2.html

On a related not, I also came up with a couple string comparison functions, find them here on CodeReview.SE

These functions are tremendously useful for improving VB6 readability, especially if you've been spoiled with .net code lately and suddenly are required to dive into a VB6 code base... Enjoy!

Answer 1

I couldn't find one anywhere, so I made my own:

Public PADDING_CHAR As String  Public Function StringFormat(format_string As String, ParamArray values()) As String 'VB6 implementation of .net String.Format(), slightly customized. 'Tested with Office 2010 VBA (x64)          Dim return_value As String         Dim values_count As Integer          'some error-handling constants:         Const ERR_FORMAT_EXCEPTION As Long = vbObjectError Or 9001         Const ERR_ARGUMENT_NULL_EXCEPTION As Long = vbObjectError Or 9002         Const ERR_SOURCE As String = "StringFormat"         Const ERR_MSG_INVALID_FORMAT_STRING As String = "Invalid format string."         Const ERR_MSG_FORMAT_EXCEPTION As String = "The number indicating an argument to format is less than zero, or greater than or equal to the length of the args array."          'use SPACE as default padding character         If PADDING_CHAR = vbNullString Then PADDING_CHAR = Chr$(32)          'figure out number of passed values:         values_count = UBound(values) + 1          Dim regex As RegExp         Dim matches As MatchCollection         Dim thisMatch As Match         Dim thisString As String         Dim thisFormat As String          'when format_string starts with "@", escapes are not replaced          '(string is treated as a literal string with placeholders)                 Dim useLiteral As Boolean          Dim escapeHex As Boolean 'indicates whether HEX specifier "0x" is to be escaped or not         'validate string_format:         Set regex = New RegExp         regex.Pattern = "{({{)*(\w+)(,-?\d+)?(:[^}]+)?}(}})*"         regex.IgnoreCase = True         regex.Global = True         Set matches = regex.Execute(format_string)          'determine if values_count matches number of unique regex matches:         Dim uniqueCount As Integer         Dim tmpCSV As String         For Each thisMatch In matches             If Not StringContains(tmpCSV, thisMatch.SubMatches(1)) Then                 uniqueCount = uniqueCount + 1                 tmpCSV = tmpCSV & thisMatch.SubMatches(1) & ","             End If         Next          'unique indices count must match values_count:         If matches.Count > 0 And uniqueCount <> values_count Then _             Err.Raise ERR_FORMAT_EXCEPTION, _             ERR_SOURCE, ERR_MSG_FORMAT_EXCEPTION          useLiteral = StringStartsWith("@", format_string)          'remove the "@" literal specifier         If useLiteral Then format_string = Right(format_string, Len(format_string) - 1)          If Not useLiteral And StringContains(format_string, "\\") Then _             format_string = Replace(format_string, "\\", Chr$(27))          If StringContains(format_string, "\\") Then _             format_string = Replace(format_string, "\\", Chr$(27))          If matches.Count = 0 And format_string <> vbNullString And UBound(values) = -1 Then         'only format_string was specified: skip to checking escape sequences:             return_value = format_string             GoTo checkEscapes         ElseIf UBound(values) = -1 And matches.Count > 0 Then             Err.Raise ERR_ARGUMENT_NULL_EXCEPTION, _                 ERR_SOURCE, ERR_MSG_FORMAT_EXCEPTION         End If          return_value = format_string          'dissect format_string:          Dim i As Integer, v As String, p As String 'i: iterator; v: value; p: placeholder         Dim alignmentGroup As String, alignmentSpecifier As String         Dim formattedValue As String, alignmentPadding As Integer          'iterate regex matches (each match is a placeholder):         For i = 0 To matches.Count - 1              'get the placeholder specified index:             Set thisMatch = matches(i)             p = thisMatch.SubMatches(1)              'if specified index (0-based) > uniqueCount (1-based), something's wrong:             If p > uniqueCount - 1 Then _                 Err.Raise ERR_FORMAT_EXCEPTION, _                 ERR_SOURCE, ERR_MSG_FORMAT_EXCEPTION             v = values(p)              'get the alignment specifier if it is specified:             alignmentGroup = thisMatch.SubMatches(2)             If alignmentGroup <> vbNullString Then _                 alignmentSpecifier = Right$(alignmentGroup, LenB(alignmentGroup) / 2 - 1)               'get the format specifier if it is specified:             thisString = thisMatch.Value             If StringContains(thisString, ":") Then                  Dim formatGroup As String, precisionSpecifier As Integer                 Dim formatSpecifier As String, precisionString As String                  'get the string between ":" and "}":                 formatGroup = Mid$(thisString, InStr(1, thisString, ":") + 1, (LenB(thisString) / 2) - 2)                 formatGroup = Left$(formatGroup, LenB(formatGroup) / 2 - 1)                  precisionString = Right$(formatGroup, LenB(formatGroup) / 2 - 1)                 formatSpecifier = Mid$(thisString, InStr(1, thisString, ":") + 1, 1)                  'applicable formatting depends on the type of the value (yes, GOTO!!):                 If TypeName(values(p)) = "Date" Then GoTo DateTimeFormatSpecifiers                 If v = vbNullString Then GoTo ApplyStringFormat  NumberFormatSpecifiers:                 If precisionString <> vbNullString And Not IsNumeric(precisionString) Then _                     Err.Raise ERR_FORMAT_EXCEPTION, _                         ERR_SOURCE, ERR_MSG_INVALID_FORMAT_STRING                  If precisionString = vbNullString Then precisionString = 0                  Select Case formatSpecifier                      Case "C", "c" 'CURRENCY format, formats string as currency.                     'Precision specifier determines number of decimal digits.                     'This implementation ignores regional settings                     '(hard-coded group separator, decimal separator and currency sign).                      precisionSpecifier = CInt(precisionString)                     thisFormat = "#,##0.$"                      If LenB(formatGroup) > 2 And precisionSpecifier > 0 Then                          'if a non-zero precision is specified...                         thisFormat = _                         Replace$(thisFormat, ".", "." & String$(precisionString, Chr$(48)))                     End If                       Case "D", "d" 'DECIMAL format, formats string as integer number.                     'Precision specifier determines number of digits in returned string.                       precisionSpecifier = CInt(precisionString)                     thisFormat = "0"                     thisFormat = Right$(String$(precisionSpecifier, "0") & thisFormat, _                         IIf(precisionSpecifier = 0, Len(thisFormat), precisionSpecifier))                       Case "E", "e" 'EXPONENTIAL NOTATION format (aka "Scientific Notation")                     'Precision specifier determines number of decimals in returned string.                     'This implementation ignores regional settings'                     '(hard-coded decimal separator).                       precisionSpecifier = CInt(precisionString)                     thisFormat = "0.00000#" & formatSpecifier & "-#" 'defaults to 6 decimals                      If LenB(formatGroup) > 2 And precisionSpecifier > 0 Then                         'if a non-zero precision is specified...                         thisFormat = "0." & String$(precisionSpecifier - 1, Chr$(48)) & "#" & formatSpecifier & "-#"                      ElseIf LenB(formatGroup) > 2 And precisionSpecifier = 0 Then                         Err.Raise ERR_FORMAT_EXCEPTION, _                             ERR_SOURCE, ERR_MSG_INVALID_FORMAT_STRING                     End If                       Case "F", "f" 'FIXED-POINT format                     'Precision specifier determines number of decimals in returned string.                     'This implementation ignores regional settings'                     '(hard-coded decimal separator).                      precisionSpecifier = CInt(precisionString)                     thisFormat = "0"                     If LenB(formatGroup) > 2 And precisionSpecifier > 0 Then                         'if a non-zero precision is specified...                         thisFormat = (thisFormat & ".") & String$(precisionSpecifier, Chr$(48))                     Else                         'no precision specified - default to 2 decimals:                         thisFormat = "0.00"                     End If                       Case "G", "g" 'GENERAL format (recursive)                     'returns the shortest of either FIXED-POINT or SCIENTIFIC formats in case of a Double.                     'returns DECIMAL format in case of a Integer or Long.                      Dim eNotation As String, ePower As Integer, specifier As String                     precisionSpecifier = IIf(CInt(precisionString) > 0, CInt(precisionString), _                         IIf(StringContains(v, "."), Len(v) - InStr(1, v, "."), 0))                      'track character case of formatSpecifier:                     specifier = IIf(formatSpecifier = "G", "D", "d")                      If TypeName(values(p)) = "Integer" Or TypeName(values(p)) = "Long" Then                         'Integer types: use {0:D} (recursive call):                         formattedValue = StringFormat("{0:" & specifier & "}", values(p))                      ElseIf TypeName(values(p)) = "Double" Then                         'Non-integer types: use {0:E}                         specifier = IIf(formatSpecifier = "G", "E", "e")                          'evaluate the exponential notation value (recursive call):                         eNotation = StringFormat("{0:" & specifier & "}", v)                          'get the power of eNotation:                         ePower = Mid$(eNotation, InStr(1, UCase$(eNotation), "E-") + 1, Len(eNotation) - InStr(1, UCase$(eNotation), "E-"))                          If ePower > -5 And Abs(ePower) < precisionSpecifier Then                             'use {0:F} when ePower > -5 and abs(ePower) < precisionSpecifier:                             'evaluate the floating-point value (recursive call):                              specifier = IIf(formatSpecifier = "G", "F", "f")                              formattedValue = StringFormat("{0:" & formatSpecifier & _                                  IIf(precisionSpecifier <> 0, precisionString, vbNullString) & "}", values(p))                         Else                             'fallback to {0:E} if previous rule didn't apply:                             formattedValue = eNotation                         End If                      End If                      GoTo AlignFormattedValue 'Skip the "ApplyStringFormat" step, it's applied already.                       Case "N", "n" 'NUMERIC format, formats string as an integer or decimal number.                     'Precision specifier determines number of decimal digits.                     'This implementation ignores regional settings'                     '(hard-coded group and decimal separators).                      precisionSpecifier = CInt(precisionString)                     If LenB(formatGroup) > 2 And precisionSpecifier > 0 Then                         'if a non-zero precision is specified...                         thisFormat = "#,##0"                         thisFormat = (thisFormat & ".") & String$(precisionSpecifier, Chr$(48))                      Else 'only the "D" is specified                         thisFormat = "#,##0"                     End If                       Case "P", "p" 'PERCENT format. Formats string as a percentage.                     'Value is multiplied by 100 and displayed with a percent symbol.                     'Precision specifier determines number of decimal digits.                      thisFormat = "#,##0%"                     precisionSpecifier = CInt(precisionString)                     If LenB(formatGroup) > 2 And precisionSpecifier > 0 Then                         'if a non-zero precision is specified...                         thisFormat = "#,##0"                         thisFormat = (thisFormat & ".") & String$(precisionSpecifier, Chr$(48))                      Else 'only the "P" is specified                         thisFormat = "#,##0"                     End If                      'Append the percentage sign to the format string:                     thisFormat = thisFormat & "%"                       Case "R", "r" 'ROUND-TRIP format (a string that can round-trip to an identical number)                     'example: ?StringFormat("{0:R}", 0.0000000001141596325677345362656)                     '         ...returns "0.000000000114159632567735"                      'convert value to a Double (chop off overflow digits):                     v = CDbl(v)                       Case "X", "x" 'HEX format. Formats a string as a Hexadecimal value.                     'Precision specifier determines number of total digits.                     'Returned string is prefixed with "&H" to specify Hex.                      v = Hex(v)                     precisionSpecifier = CInt(precisionString)                      If LenB(precisionString) > 0 Then 'precision here stands for left padding                         v = Right$(String$(precisionSpecifier, "0") & v, IIf(precisionSpecifier = 0, Len(v), precisionSpecifier))                     End If                      'add C# hex specifier, apply specified casing:                     '(VB6 hex specifier would cause Format() to reverse the formatting):                     v = "0x" & IIf(formatSpecifier = "X", UCase$(v), LCase$(v))                       Case Else                          If IsNumeric(formatSpecifier) And val(formatGroup) = 0 Then                             formatSpecifier = formatGroup                             v = Format(v, formatGroup)                         Else                             Err.Raise ERR_FORMAT_EXCEPTION, _                                 ERR_SOURCE, ERR_MSG_INVALID_FORMAT_STRING                         End If                 End Select                  GoTo ApplyStringFormat   DateTimeFormatSpecifiers:                 Select Case formatSpecifier                      Case "c", "C" 'CUSTOM date/time format                     'let VB Format() parse precision specifier as is:                         thisFormat = precisionString                      Case "d" 'SHORT DATE format                         thisFormat = "ddddd"                       Case "D" 'LONG DATE format                         thisFormat = "dddddd"                      Case "f" 'FULL DATE format (short)                         thisFormat = "dddddd h:mm AM/PM"                      Case "F" 'FULL DATE format (long)                         thisFormat = "dddddd ttttt"                      Case "g"                         thisFormat = "ddddd hh:mm AM/PM"                      Case "G"                         thisFormat = "ddddd ttttt"                      Case "s" 'SORTABLE DATETIME format                         thisFormat = "yyyy-mm-ddThh:mm:ss"                      Case "t" 'SHORT TIME format                         thisFormat = "hh:mm AM/PM"                      Case "T" 'LONG TIME format                         thisFormat = "ttttt"                      Case Else                         Err.Raise ERR_FORMAT_EXCEPTION, _                             ERR_SOURCE, ERR_MSG_INVALID_FORMAT_STRING                 End Select                 GoTo ApplyStringFormat              End If   ApplyStringFormat:             'apply computed format string:             formattedValue = Format(v, thisFormat)   AlignFormattedValue:             'apply specified alignment specifier:             If alignmentSpecifier <> vbNullString Then                  alignmentPadding = Abs(CInt(alignmentSpecifier))                 If CInt(alignmentSpecifier) < 0 Then                     'negative: left-justified alignment                     If alignmentPadding - Len(formattedValue) > 0 Then _                         formattedValue = formattedValue & _                             String$(alignmentPadding - Len(formattedValue), PADDING_CHAR)                 Else                     'positive: right-justified alignment                     If alignmentPadding - Len(formattedValue) > 0 Then _                         formattedValue = String$(alignmentPadding - Len(formattedValue), PADDING_CHAR) & formattedValue                 End If             End If              'Replace C# hex specifier with VB6 hex specifier,              'only if hex specifier was introduced in this function:             If (Not useLiteral And escapeHex) And _                 StringContains(formattedValue, "0x") Then _             formattedValue = Replace$(formattedValue, "0x", "&H")              'replace all occurrences of placeholder {i} with their formatted values:             return_value = Replace(return_value, thisString, formattedValue, Count:=1)              'reset before reiterating:             thisFormat = vbNullString         Next   checkEscapes:         'if there's no more backslashes, don't bother checking for the rest:         If useLiteral Or Not StringContains(return_value, "\") Then GoTo normalExit          Dim escape As New EscapeSequence         Dim escapes As New Collection         escapes.Add escape.Create("\n", vbNewLine), "0"         escapes.Add escape.Create("\q", Chr$(34)), "1"         escapes.Add escape.Create("\t", vbTab), "2"         escapes.Add escape.Create("\a", Chr$(7)), "3"         escapes.Add escape.Create("\b", Chr$(8)), "4"         escapes.Add escape.Create("\v", Chr$(13)), "5"         escapes.Add escape.Create("\f", Chr$(14)), "6"         escapes.Add escape.Create("\r", Chr$(15)), "7"          For i = 0 To escapes.Count - 1             Set escape = escapes(CStr(i))             If StringContains(return_value, escape.EscapeString) Then _                 return_value = Replace(return_value, escape.EscapeString, escape.ReplacementString)              If Not StringContains(return_value, "\") Then _                 GoTo normalExit         Next          'replace "ASCII (oct)" escape sequence         Set regex = New RegExp         regex.Pattern = "\\(\d{3})"         regex.IgnoreCase = True         regex.Global = True         Set matches = regex.Execute(format_string)          Dim char As Long         If matches.Count <> 0 Then             For Each thisMatch In matches                 p = thisMatch.SubMatches(0)                 '"p" contains the octal number representing the ASCII code we're after:                 p = "&O" & p 'prepend octal prefix                 char = CLng(p)                 return_value = Replace(return_value, thisMatch.Value, Chr$(char))             Next         End If          'if there's no more backslashes, don't bother checking for the rest:         If Not StringContains("\", return_value) Then GoTo normalExit          'replace "ASCII (hex)" escape sequence         Set regex = New RegExp         regex.Pattern = "\\x(\w{2})"         regex.IgnoreCase = True         regex.Global = True         Set matches = regex.Execute(format_string)          If matches.Count <> 0 Then             For Each thisMatch In matches                 p = thisMatch.SubMatches(0)                 '"p" contains the hex value representing the ASCII code we're after:                 p = "&H" & p 'prepend hex prefix                 char = CLng(p)                 return_value = Replace(return_value, thisMatch.Value, Chr$(char))             Next         End If  normalExit:         Set escapes = Nothing         Set escape = Nothing         If Not useLiteral And StringContains(return_value, Chr$(27)) Then _             return_value = Replace(return_value, Chr$(27), "\")         StringFormat = return_value End Function 

Notice the ParamArray in the method signature (thanks @wqw): doing so spares the usage of multiple optional parameters (and from usage bugs with being able to assign value2 without assigning value1 when naming the parameters in the calling statement). Because it's a ParamArray, the individual values are Variant which means every parameter could be of a different type, VB is doing the string conversion behind the scenes.

The function can then be consumed like this:

?StringFormat("(C) Currency: . . . . . . . . {0:C}\n" & _     "(D) Decimal:. . . . . . . . . {0:D}\n" & _     "(E) Scientific: . . . . . . . {1:E}\n" & _     "(F) Fixed point:. . . . . . . {1:F}\n" & _     "(N) Number: . . . . . . . . . {0:N}\n" & _     "(P) Percent:. . . . . . . . . {1:P}\n" & _     "(R) Round-trip: . . . . . . . {1:R}\n" & _     "(X) Hexadecimal:. . . . . . . {0:X}\n",-123, -123.45) 

Output:

(C) Currency: . . . . . . . . -123.00$ (D) Decimal:. . . . . . . . . -123 (E) Scientific: . . . . . . . -1.23450E2 (F) Fixed point:. . . . . . . -123 (N) Number: . . . . . . . . . -123 (P) Percent:. . . . . . . . . -12,345% (R) Round-trip: . . . . . . . -123.45 (X) Hexadecimal:. . . . . . . &HFFFFFF85 

And also like this:

?StringFormat("(c) Custom format: . . . . . .{0:cYYYY-MM-DD (MMMM)}\n" & _     "(d) Short date: . . . . . . . {0:d}\n" & _     "(D) Long date:. . . . . . . . {0:D}\n" & _     "(T) Long time:. . . . . . . . {0:T}\n" & _     "(f) Full date/short time: . . {0:f}\n" & _     "(F) Full date/long time:. . . {0:F}\n" & _     "(s) Sortable: . . . . . . . . {0:s}\n", Now()) 

Output:

(c) Custom format: . . . . . .2013-01-26 (January) (d) Short date: . . . . . . . 1/26/2013 (D) Long date:. . . . . . . . Saturday, January 26, 2013 (T) Long time:. . . . . . . . 8:28:11 PM (f) Full date/short time: . . 1/26/2013 8:28:11 PM (F) Full date/long time:. . . Saturday, January 26, 2013 8:28:11 PM (s) Sortable: . . . . . . . . 2013-01-26T20:28:11 

Also possible to specify alignment (/padding) and to use escape sequences:

?StringFormat ("\q{0}, {1}!\x20\n'{2,10:C2}'\n'{2,-10:C2}'", "hello", "world", 100)  "hello, world!" '   100.00$' '100.00$   ' 

Looking at samples from http://msdn.microsoft.com/fr-fr/library/b1csw23d(v=vs.80).aspx, only a few format specifiers are not implemented, mostly date/time specifiers... but I would think the "c" custom date/time format specifier makes it up.

The function uses a straightforward implementation of String.Contains():

Public Function StringContains(string_source As String, find_text As String, _     Optional ByVal caseSensitive As Boolean = True) As Boolean     StringContains = StringContainsAny(string_source, caseSensitive, find_text) End Function 

EDIT: This code now properly handles "\\" escapes, as mentioned in the comments. Also, while StringContains is certainly practical and gives a more comfortable reading than an InStr() call, the below StringContainsAny function is even better:

Public Function StringContainsAny(string_source As String, ByVal caseSensitive As Boolean, _     ParamArray find_values()) As Boolean      Dim i As Integer, found As Boolean     If caseSensitive Then         For i = LBound(find_values) To UBound(find_values)             found = (InStr(1, string_source, _                 find_values(i), vbBinaryCompare) <> 0)             If found Then Exit For         Next     Else         For i = LBound(find_values) To UBound(find_values)             StringContainsAny = (InStr(1, LCase$(string_source), _                  LCase$(find_values(i)),   vbBinaryCompare) <> 0)             If found Then Exit For         Next     End If     StringContainsAny = found End Function 

Consider the following:

foo = Instr(1, source, "value1") > 0 Or Instr(1, source, "value2") > 0 _    Or Instr(1, source, "value3") > 0 Or Instr(1, source, "value4") > 0 _    Or Instr(1, source, "value5") > 0 Or Instr(1, source, "value6") > 0 _ 

Before VB can determine if foo is TRUE or FALSE, every single InStr() call is made. However with StringContainsAny(), the condition is satisfied with the first value that gets found, which makes it a faster statement.

EDIT: Previous edit pretty much wiped out escape sequences; reinstated them, using a small class "EscapeSequence" exposing two properties and a factory method - doing this allows keeping the for-each loop and handling all simple escapes without duplicating much code.

This code also uses a StringStartsWith function, implemented like this:

Public Function StringStartsWith(ByVal find_text As String, ByVal string_source As String, Optional ByVal caseSensitive As Boolean = True) As Boolean      If caseSensitive Then         StringStartsWith = (Left$(string_source, LenB(find_text) / 2) = find_text)     Else         StringStartsWith = (Left$(LCase(string_source), LenB(find_text) / 2) = LCase$(find_text))     End If  End Function