Precompilers, OCI & OCCI :: Data Lost After Adding Null Terminator For VARCHAR Data Received From Database

We are migrating a proc application as described below.

Old Env: UNIX
Old DB: Oracle 8i

New Env: Linux
New DB: Oracle 11g

New modules are successfully compiled in Linux environment. But we are facing issues in writing the output of VARCHAR datatype to a file.

find below the extract of code.
EXEC SQL BEGIN DECLARE SECTION;
varchar mcolmnvarchar[4];
EXEC SQL END DECLARE SECTION;

EXEC SQL DECLARE crs CURSOR FOR
SELECT NVL(colmn,' ') FROM table1

memset(mcolmnvarchar.arr,'�',4); //Was added for only Linux migration. Not present in unix env.

EXEC SQL FETCH c1 INTO :mcolmnvarchar;

cout << "Data at Stage one"<< mcolmnvarchar << endl;
mcolmnvarchar.arr[mcolmnvarchar.len]='�';
cout << "Data at Stage two"<< mcolmnvarchar << endl;
fprintf(fptr,"%-4s",mcolmnvarchar.arr);

Above code works absolutely fine in Unix env with Oracle 8i. But with Linux env & Oracle 11g it is not working. No compilation or run time errors. Data at Stage one prints the output of database properly. But after null terminator code, Data at Stage two statement prints without any value. Value is lost after null terminator code.