source: UsbWattMeter/trunk/curl-7.47.1/include/README@ 164

                                  _   _ ____  _
                              ___| | | |  _ \| |
                             / __| | | | |_) | |
                            | (__| |_| |  _ <| |___
                             \___|\___/|_| \_\_____|

Include files for libcurl, external users.

They're all placed in the curl subdirectory here for better fit in any kind
of environment. You must include files from here using...

        #include <curl/curl.h>

... style and point the compiler's include path to the directory holding the
curl subdirectory. It makes it more likely to survive future modifications.

NOTE FOR LIBCURL HACKERS

The following notes apply to libcurl version 7.19.0 and later.

* The distributed curl/curlbuild.h file is only intended to be used on systems
  which can not run the also distributed configure script.

* The distributed curlbuild.h file is generated as a copy of curlbuild.h.dist
  when the libcurl source code distribution archive file is originally created.

* If you check out from git on a non-configure platform, you must run the
  appropriate buildconf* script to set up curlbuild.h and other local files
  before being able of compiling the library.

* On systems capable of running the configure script, the configure process
  will overwrite the distributed include/curl/curlbuild.h file with one that
  is suitable and specific to the library being configured and built, which
  is generated from the include/curl/curlbuild.h.in template file.

* If you intend to distribute an already compiled libcurl library you _MUST_
  also distribute along with it the generated curl/curlbuild.h which has been
  used to compile it. Otherwise the library will be of no use for the users of
  the library that you have built. It is _your_ responsibility to provide this
  file. No one at the cURL project can know how you have built the library.

* File curl/curlbuild.h includes platform and configuration dependent info,
  and must not be modified by anyone. Configure script generates it for you.

* We cannot assume anything else but very basic compiler features being
  present. While libcurl requires an ANSI C compiler to build, some of the
  earlier ANSI compilers clearly can't deal with some preprocessor operators.

* Newlines must remain unix-style for older compilers' sake.

* Comments must be written in the old-style /* unnested C-fashion */

To figure out how to do good and portable checks for features, operating
systems or specific hardwarare, a very good resource is Bjorn Reese's
collection at http://predef.sf.net/