Perform code-set conversion

For a multibyte-character string, the size of the converted string might not equal the size of the unconverted string. Therefore, to perform code-set conversion on multibyte characters, you must take the following special processing steps:

• Determine whether you need to allocate a separate destination buffer; if a destination buffer is needed, determine its size.
• Preserve state information for multiple fragments of a multibyte string.