How to use PREFIX created by autoconf in source file

[Adam Jiang]

Autoconf could help to generate configure script which accepts an option
called --prefix in general. In this way, users could specific a path where
programs/data installed.

In my program, I'd like to refer the location where data files are
installed. In plain Makefile, it could be done like

gcc -DPREFIX "/usr/share"

and in the source file, data path is generated in

#define DATAPATH PREFIX "/data"

with autoconf, how could I use the path specified by --prefix in source
code? Is there a pre-defined MACRO for this?