how to be compiled under different OS like sqlite.c

[vertextao]

As some of you may know that sqlite.c can be compiled in different os like WIN/Linux/OS2... without any configuration.

how to detect which code segment(platform dependent) to be used? how can this be done? Can anyone give a solution to do this?
Just share your experience here!!!
Thanks!!!

---------- Post added at 10:45 AM ---------- Previous post was at 10:19 AM ----------

I do find the key macro definition here!!!

#if defined(SQLITE_OS_OTHER)
# if SQLITE_OS_OTHER==1
# undef SQLITE_OS_UNIX
# define SQLITE_OS_UNIX 0
# undef SQLITE_OS_WIN
# define SQLITE_OS_WIN 0
# undef SQLITE_OS_OS2
# define SQLITE_OS_OS2 0
# else
# undef SQLITE_OS_OTHER
# endif
#endif
#if !defined(SQLITE_OS_UNIX) && !defined(SQLITE_OS_OTHER)
# define SQLITE_OS_OTHER 0
# ifndef SQLITE_OS_WIN
# if defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)
# define SQLITE_OS_WIN 1
# define SQLITE_OS_UNIX 0
# define SQLITE_OS_OS2 0
# elif defined(__EMX__) || defined(_OS2) || defined(OS2) || defined(_OS2_) || defined(__OS2__)
# define SQLITE_OS_WIN 0
# define SQLITE_OS_UNIX 0
# define SQLITE_OS_OS2 1
# else
# define SQLITE_OS_WIN 0
# define SQLITE_OS_UNIX 1
# define SQLITE_OS_OS2 0
# endif
# else
# define SQLITE_OS_UNIX 0
# define SQLITE_OS_OS2 0
# endif
#else
# ifndef SQLITE_OS_WIN
# define SQLITE_OS_WIN 0
# endif
#endif

[stevea]

gcc will predefine "__linux" or similar for other OSes - but techincally that describes the compile or config environemnt - not necessarily the target environment.

cpp -dM </dev/null

lists the predefined macros.

=============

It's more ideal to use the ./configure script to identify the target environment.