@mrjj Hey bro thanks a lot that article was help me a lot to solve it.

@Paul-Colby i am opening xml file as you mentioned
first time when i pressed save button it will show
<?xml version='1.0'?>
<xml>
<tag1> </tag1> // two spaces from line edit
</xml>

second time when i presses save button it will show

<?xml version='1.0'?>
<xml>
<tag1/> // some data in lineedit
</xml>

third time when i presses save button it will show

<?xml version='1.0'?>
<xml>
<tag1/> // some data in lineedit
</xml>

i am using Qt 4.8.7, i am opening xml file , see the result

@JonBriem
Most welcome. If possible,please edit the first post you made and add [SOLVED] in front of title.