C++ XML save unit problems

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XML

QT

sorry,i didn't find qt zones,so i put my questions here,
it was like this:

i use qt4.5.3 and xerces-c-3.0.1 to read xml file,
then when i save my files, a problem occurs,
m³---change into m3;m² change into m2;

my xml format is UTF-8, i searched many websites,
and still don't get a solution, so i write here
to get help,thanks:)