Sorry Mr.Wysota
Its my mistake, i should post my thread with clear codes and explanations. sorry once again.

the retrieved value from xml file is in binary base64 encoded, so i created another one byte array (byte) to store the base64 decoded binary data, for that i used the following syntax...

Qt Code: 
  1. QByteArray byte(QByteArray::fromBase64(wBData1));
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then im storing the contents of the variable byto into a already opened file, code given below

Qt Code: 
  1. fil.write(byte);
  2.         fil.close();
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fil is file object already opened,

after doing all these things i could not get the original file (for eg image) what im stored before into the server.