duilio foschi wrote

It is still not clear to me where to place the compiled code.

Whatever the webserver defined as a location where cgi apps can be executable. On ubuntu this is by default: /usr/lib/cgi-bin/

But I normally enable my users own public directory as cgi friend. eg: ~/public_html/

That way I can quickly and easily test a cgi apps without requiring sudo (root) access. The example project I posted before was run from: ~/public_html/test/cgitest.cgi
and was accessible via the web browser as:
http://127.0.0.1/~graemeg/test/cgitest.cgi

Using the .cgi extension is my personal preference. That makes it easier for me to distinguish between GUI, Console and CGI applications on my system.

I don't think that the browser can access any part of the disk, so the CGI application has to be copied in some accessible directory... but which one ?

On Ubuntu, that is normally /usr/lib/cgi-bin/
Problem with this is, you need sudo (root/admin) rights to write to that directory, that is why I enable cgi support in my home directory.

However how can I be sure of it ?

Copy it into the above location and try and access it via a web browser

http://<your_ubuntu_webserver>/cgi-bin/cgitest.cgi