Thnaks for the inputs.
Now I have found a way to make my <COUNTER> non editable using the mask

Qt Code: 
  1. lineEdit->setInputMask("xxxx\<\C\O\U\N\T\E\R\>");
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Now thw problem is I am able to enter only 4 characters before <COUNTER> but i want to allow the user to enter maximum of 91 charcters.

What should I modify on the reg expression to achieve this?