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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.
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
WTERMSIGmacro.int w_coredump- The value of this member is the same as that of the
WCOREDUMPmacro.int w_retcode- The value of this member is the same as that of the
WEXITSTATUSmacro.int w_stopsig- The value of this member is the same as that of the
WSTOPSIGmacro.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.
If usage is a null pointer,
wait3is equivalent towaitpid (-1,status-ptr,options).If usage is not null,
wait3stores usage figures for the child process in*rusage (but only if the child has terminated, not if it has stopped). See Resource Usage.