Some code needs modifications or conditional compilation based upon what version of FreeBSD Unix it is running under. The preferred way to tell FreeBSD versions apart are the __FreeBSD_version and __FreeBSD__ macros defined in sys/param.h. If this file is not included add the code,

#include <sys/param.h>

to the proper place in the .c file.

__FreeBSD__ is defined in all versions of FreeBSD as their major version number. For example, in FreeBSD 9.x, __FreeBSD__ is defined to be 9.

#if __FreeBSD__ >= 9
#  if __FreeBSD_version >= 901000
	 /* 9.1+ release specific code here */
#  endif
#endif

A complete list of __FreeBSD_version values is available in Chapter 16, __FreeBSD_version Values.