I'd do:
Qt Code: 
  1. float extractCmd(const QString &str, const QString &expected){
  2.   if(expected.size()>2 || str.size()<4) return 0;
  3.   QStringList commands = str.simplified().split(",");
  4.   static QRegExp rx("([A-Z][A-Z])#([0-9]*\\.?[0-9]+)");
  5.   foreach(QString cmd, commands){
  6.     if(!rx.exactMatch(cmd))
  7.       continue;
  8.     if(rx.cap(1)==expected)
  9.       return rx.cap(2).toFloat();
  10.   }
  11. }
  12.  
  13. QString str = "DV#1200.03,AB#34,SH#100\r\n\0";
  14. float val = extractCmd(str, "SH");
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