How to make it possible to use this code from shared library ?

I think (untested) it's just that the XS file that Inline generates specifies "PACKAGE = main", whereas for your purposes here, it needs to specify "PACKAGE = Example". Specifying NAME => 'Example' sets "MODULE = Example", but doesn't set PACKAGE appropriate to your needs.

If, having installed InlineX::C2XS you put that C code (only the C code - nothing else) into ./src/Example.c, create a directory named (say) ./MyMod, and run this script:

use warnings;
use strict;
use InlineX::C2XS qw(c2xs);

c2xs('Example', 'Example', './MyMod');
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Then you should get a correct XS file for inclusion in a perl module/package named 'Example'.
You can also provide arguments to c2xs() to auto-generate a Makefile.PL, Example.pm, and MANIFEST files, thereby making it easy to build your 'Example' module in the usual manner (and with no dependency upon Inline::C).

As regards the "main" function in the code you provided, it seems to be working fine - but it's just another subroutine, and it's therefore best to call it something other than "main" (to avoid confusion).

Cheers,Rob