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Untabify and Tabify

, 16 Jan 2009
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Untabify and Tabify Extension Methods for intending code.

Background

In the never-ending debate over whether to use SPACEs or TABs for indenting code, I prefer SPACEs. Having mentioned that I had written an Untabify utility, I was asked for an article. I have now rewritten the code in C#, and added a companion Tabify utility for readers who are in that camp. I implemented the methods as Extension Methods. I'm not a fan of Extension Methods, but this seemed like a reasonable use for them.

Another implementation choice was to keep the general layout of the two methods similar. At first, I wrote Untabify with a switch, but the switch was problematic in Tabify, so I changed both to use nested ifs.

Both methods use a StringBuilder, and stop processing the string as soon as a non-whitespace character or the end of the line is reached.

Untabify method

The Untabify method iterates the string, appending any SPACEs it encounters, and replacing any TAB characters with an appropriate number of SPACEs to reach the next tab stop. If the caller specifies four SPACEs per indent and a string begins with [ SPACE SPACE TAB ], then the TAB will be replaced by two SPACEs.

The caller may also specify zero SPACEs per indent to simply remove TABs from the leading whitespace.

public static string
Untabify
(
    this string String
,
    byte        SpacesPerIndent
)
{
    /* Let it throw the Exception */
    System.Text.StringBuilder result = 
       new System.Text.StringBuilder ( String.Length ) ;
 
    int offset = 0 ;
 
    while ( offset < String.Length )
    {
        if ( String [ offset ] == ' ' )
        {
            result.Append ( ' ' ) ;
 
            offset++ ;
        }
        else
        {
            if ( String [ offset ] == '\t' )
            {
                if ( SpacesPerIndent > 0 )
                {
                    for ( int i = result.Length % SpacesPerIndent ; 
                          i < SpacesPerIndent ; i++ )
                    {
                        result.Append ( ' ' ) ;
                    }
                }
 
                offset++ ;
            }
            else
            {
                break ;
            }
        }
    }
 
    result.Append ( String.Substring ( offset ) ) ;
 
    return ( result.ToString() ) ;
}

Tabify method

The Tabify method iterates the string, appending any TABs it encounters and removing any SPACE characters. If the caller specifies four SPACEs per indent and a string begins with [ SPACE SPACE TAB ], then the two SPACEs will be removed.

A contiguous sequence of SPACEs of length equal to SpacesPerIndent will cause a TAB to be appended. If the caller specifies four SPACEs per indent and a string begins with [ SPACE SPACE SPACE SPACE ], then the four SPACEs will be replaced by a TAB.

The caller may also specify zero SPACEs per indent to simply remove SPACEs from the leading whitespace.

(See below for information on TabifyMode.)

public static string
Tabify
(
    this string String
,
    byte        SpacesPerIndent
,
    TabifyMode  Mode
)
{
    /* Let it throw the Exception */
    System.Text.StringBuilder result = 
       new System.Text.StringBuilder ( String.Length ) ;
 
    int offset = 0 ;
    int spaces = 0 ;
 
    while ( offset < String.Length )
    {
        if ( String [ offset ] == ' ' )
        {
            if ( ++spaces == SpacesPerIndent )
            {
                result.Append ( '\t' ) ;
 
                spaces = 0 ;
            }
 
            offset++ ;
        }
        else
        {
            if ( String [ offset ] == '\t' )
            {
                result.Append ( '\t' ) ;
 
                spaces = 0 ;
 
                offset++ ;
            }
            else
            {
                break ;
            }
        }
    }
 
    switch ( Mode )
    {
        case TabifyMode.Retain :
        {
            while ( spaces-- > 0 )
            {
                result.Append ( ' ' ) ;
            }
 
            break ;
        }
 
        case TabifyMode.Extend :
        {
            result.Append ( '\t' ) ;
 
            break ;
        }
    }
 
    result.Append ( String.Substring ( offset ) ) ;
 
    return ( result.ToString() ) ;
}

TabifyMode enumeration

The TabifyMode enumeration controls what Untabify does with "extra" SPACEs.

If the caller specifies four SPACEs per indent and a string begins with [ SPACE SPACE SPACE SPACE SPACE SPACE NON-WHITESPACE ], the first four SPACEs cause one TAB to be appended, but what does the caller want to do with the other two?

Visual Studio's tabify feature will leave the two SPACEs in place, so that's the default behavior (Retain). The caller may specify Truncate to remove them, or Extend to append a TAB in their place.

public enum TabifyMode
{
    Retain
,
    Truncate
,
    Extend
}

Using the code

Using these methods is quite simple; they're Extension Methods, so add an appropriate using directive and use them as if they belong to the string class. I prefer to put each Extension Method (or group of overloaded ones) I write in its own namespace, so my using directives specify exactly which methods I'm importing.

using PIEBALD.Lib.LibExt.Untabify ;
using PIEBALD.Lib.LibExt.Tabify ;
 
string s = "  \t" ;
 
s.Untabify ( 4 ) ; // yields "    "
s.Tabify ( 4 ) ;   // yields "\t"

Untabify utility

This is a very simple console application that reads the lines in a file, right-trims and untabifies each, then writes each out to another file.

It can be built with csc Untabify.cs LibExt.Untabify.cs.

namespace Untabify
{
    using PIEBALD.Lib.LibExt.Untabify ;
 
    public static class Untabify
    {
        [System.STAThreadAttribute()]
        public static int
        Main
        (
            string[] args
        )
        {
            int result = 0 ;
 
            try
            {
                if ( args.Length == 3 )
                {
                    using ( System.IO.TextReader tr = 
                              new System.IO.StreamReader ( args [ 0 ] ) )
                    {
                        using ( System.IO.TextWriter tw = 
                                   new System.IO.StreamWriter ( args [ 1 ] ) )
                        {
                            byte spt = byte.Parse ( args [ 2 ] ) ;
 
                            string line ;
 
                            while ( ( line = tr.ReadLine() ) != null )
                            {
                                tw.WriteLine ( line.TrimEnd().Untabify ( spt ) ) ;
                            }
                        }
                    }
                }
                else
                {
                    System.Console.WriteLine ( "Syntax: Untabify" + 
                                   " infile outfile spacesperindent" ) ;
                }
            }
            catch ( System.Exception err )
            {
                while ( err != null )
                {
                    System.Console.WriteLine ( err ) ;

                    err = err.InnerException ;
                }
            }
 
            return ( result ) ;
        }
    }
}

Tabify utility

This is a very simple console application that reads the lines in a file, right-trims and tabifies each, then writes each out to another file.

It can be built with csc Tabify.cs LibExt.Tabify.cs.

namespace Tabify
{
    using PIEBALD.Lib.LibExt.Tabify ;
 
    public static class Tabify
    {
        [System.STAThreadAttribute()]
        public static int
        Main
        (
            string[] args
        )
        {
            int result = 0 ;
 
            try
            {
                if ( args.Length == 3 )
                {
                    using ( System.IO.TextReader tr = 
                               new System.IO.StreamReader ( args [ 0 ] ) )
                    {
                        using ( System.IO.TextWriter tw = 
                                   new System.IO.StreamWriter ( args [ 1 ] ) )
                        {
                            byte spt = byte.Parse ( args [ 2 ] ) ;
 
                            string line ;
 
                            while ( ( line = tr.ReadLine() ) != null )
                            {
                                tw.WriteLine ( line.TrimEnd().Tabify ( spt ) ) ;
                            }
                        }
                    }
                }
                else
                {
                    System.Console.WriteLine ( "Syntax: Tabify" + 
                                   " infile outfile spacesperindent" ) ;
                }
            }
            catch ( System.Exception err )
            {
                while ( err != null )
                {
                    System.Console.WriteLine ( err ) ;
 
                    err = err.InnerException ;
                }
            }
 
            return ( result ) ;
        }
    }
}

History

  • 2009-01-14 - First submitted.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

PIEBALDconsult
Software Developer (Senior)
United States United States
BSCS 1992 Wentworth Institute of Technology
 
Originally from the Boston (MA) area. Lived in SoCal for a while. Now in the Phoenix (AZ) area.
 
OpenVMS enthusiast, ISO 8601 evangelist, photographer, opinionated SOB
 
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Comments and Discussions

 
GeneralMy vote of 3 Pinmembereuggg123456785-Oct-11 13:52 
Generalliteral strings PinmvpLuc Pattyn16-Jan-09 5:43 
GeneralRe: literal strings PinmemberPIEBALDconsult16-Jan-09 6:01 

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