do I need "ifdef HAVE_UNISTD_H" if I import unistd?

[Sam Steingold]

DIUC that if I include the sys_time & unistd modules, I can write

#include <unistd.h>
#include <sys/time.h>

instead of

#ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
#endif
#ifdef HAVE_UNISTD_H
  #include <unistd.h>
#endif

??

the same question for all the other headers...

thanks!

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Sam Steingold (http://sds.podval.org/) on CentOS release 5.6 (Final) X 
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