I have used following example_style.ist file for creating index
headings_flag 1
heading_prefix "{ \\bfseries "
heading_suffix "}\\nopagebreak\\\n"
and in the preamble I have added following
\usepackage{imakeidx}
\makeindex[options= -s example_style.ist]
and got out put as
Now the header is in left alinment. But I am in need of that A and B in center.
Is it possible to change A to center?

heading_prefix "{\\bfseries\\hfil " heading_suffix "\\hfil}\\nopagebreak\n"– touhami Jun 23 '16 at 07:40