This page describes how to convert a string to or from the GSM 03.38 character set.

'''Requirements'''

   * The gsm0338 encoding must be available in the Tcl installation. Download it from http://search.cpan.org/src/JHI/perl-5.7.2/ext/Encode/Encode/ and save it as e.g. $tcl_library/encoding/gsm0338.enc
   * A TCL-Version which supports [encoding convertto] and [encoding convertfrom] (Tcl 8.1 or above)


'''The non-null 0 character "@"'''

In the GSM 03.38 character set, the character "@" is encoded as 0x00. 
[encoding convertto] interprets such characters as "not convertible" and uses
the fallback character "?". 


Example: 

    set gsmString [encoding convertto gsm0338 "me@domain.com"]
    # will return me?domain.com instead of me\x00domain.com


'''Workarounds'''

 # The string is split at each "@", and the pieces are converted
 # separately.
 proc toGsm {aString} {
  set partsWithoutAt [split $aString "@"]

  set convertedPartsWithoutAt {}
  foreach part $partsWithoutAt {
   lappend convertedPartsWithoutAt [encoding convertto gsm0338 $part]
  }

  return [join $convertedPartsWithoutAt "\x00"]
 }
 
An alternative workaround, which is shorter but relies on an implementation detail of [encoding convertto]: 

 proc toGsm {aString} {
  return [encoding convertto gsm0338 [string map {@ \x00} $aString] ]
 }