Character Conversion Plug-In Provider Overview

A character conversion plug-in DLL implements conversion between Unicode and another character set. Conversion between Unicode and several common non-Unicode (or "foreign") character sets is built into Symbian OS. Some of the conversion data is hard-coded and some is provided by plug-in DLLs.

For v6.1, the complete list of character sets for which conversion has been implemented in Symbian OS is as follows: UTF-7, UTF-8, ImapUTF-7, Java Conformant UTF-8, Code Page 1252, ISO-8859-1, ASCII, SMS 7-Bit, EUC-JP, GB 12345, GB 2312, GBK, HZ, ISO-2022-JP, ISO-2022-JP1, JIS, Shift-JIS, Big Five. It is important to note that some of these character sets may not be available at run-time, but others (e.g. those written by 3rd parties) may be available.

When preparing to convert to or from Unicode, the CCnvCharacterSetConverter class searches for and loads the plug-in DLL which implements the required conversion. The DLL's implementations of the plug-in interface (ConvertFromUnicode() and ConvertToUnicode()) can then be called by CCnvCharacterSetConverter's member functions ConvertFromUnicode() and ConvertToUnicode().

Contents of snm files are read by the CCnvCharacterSetConverter class. This information is used to convert between the character set's internet-standard name or its MIB enum value and its Symbian-specific UID value.

The following tools are involved in the creation of a character conversion plug-in.

Creating a plug-in character conversion DLL is a two-stage process cnvtool is invoked to generate a C++ file from two text files which are known as the source file and the control file. Then, the generated C++ file is compiled along with another (hand-written) C++ file to produce the DLL. For information on cnvtool syntax see the Tools and Utilities documentation, at cnvtool command syntax.

A standard names and MIB enums (snm) file should also be created if there are any standard names and/or MIB enums for the character set being implemented (see ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets). This is a data file which contains mappings between Internet standard identifiers of character sets (which may either be names or MIB enums) and their equivalent Symbian UID. It is generated by a tool called snmtool. Information about snmtool syntax is provided in the Tools and Utilities documentation, at snmtool command syntax.

Character Conversion Overview

Character conversion plug-in creation tools guide