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(libc.info)BSD Wait Functions

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BSD Process Wait Functions
==========================

   The GNU library also provides these related facilities for
compatibility with BSD Unix.  BSD uses the `union wait' data type to
represent status values rather than an `int'.  The two representations
are actually interchangeable; they describe the same bit patterns.  The
GNU C Library defines macros such as `WEXITSTATUS' so that they will
work on either kind of object, and the `wait' function is defined to
accept either type of pointer as its STATUS-PTR argument.

   These functions are declared in `sys/wait.h'.

 - Data Type: union wait
     This data type represents program termination status values.  It
     has the following members:

    `int w_termsig'
          The value of this member is the same as that of the
          `WTERMSIG' macro.

    `int w_coredump'
          The value of this member is the same as that of the
          `WCOREDUMP' macro.

    `int w_retcode'
          The value of this member is the same as that of the
          `WEXITSTATUS' macro.

    `int w_stopsig'
          The value of this member is the same as that of the
          `WSTOPSIG' macro.

     Instead of accessing these members directly, you should use the
     equivalent macros.

   The `wait3' function is the predecessor to `wait4', which is more
flexible.  `wait3' is now obsolete.

 - Function: pid_t wait3 (union wait *STATUS-PTR, int OPTIONS, struct
          rusage *USAGE)
     If USAGE is a null pointer, `wait3' is equivalent to `waitpid (-1,
     STATUS-PTR, OPTIONS)'.

     If USAGE is not null, `wait3' stores usage figures for the child
     process in `*RUSAGE' (but only if the child has terminated, not if
     it has stopped).  Note: Resource Usage.