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Wait for a child process to stop or terminate


#include <sys/types.h>
#include <sys/wait.h>

pid_t waitpid( pid_t pid,
               int * stat_loc,
               int options );


The set of child processes that you want to get status information for:
NULL, or a pointer a location where the function can store the terminating status of the child process. For information about macros that extract information from this status, see Status macros in the documentation for wait().
A combination of zero or more of the following flags:



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The waitpid() function suspends execution of the calling thread until status information from one of its terminated child processes is available, or until the delivery of a signal whose action is either to terminate the process or execute a signal handler. If status information is available prior to the call to waitpid(), the return is immediate.

The waitpid() function behaves the same as wait() when passed a pid argument of -1, and the options argument has a value of zero.

Only one of the WIFEXITED(stat_val) and WIFSIGNALED(stat_val) macros can evaluate to a nonzero value.


The process ID of the terminating child process on success. If waitpid() is invoked with WNOHANG set in options, it has at least one child process specified by pid for which status isn't available, and status isn't available for any process specified by pid, a value of zero is returned. On delivery of a signal, waitpid() returns -1, and errno is set to EINTR.


The calling process has no existing unwaited-for child processes that meet the criteria set by pid.
The function was interrupted by a signal. The value of the location pointed to by stat_loc is undefined.
The value of the options argument isn't valid.


POSIX 1003.1

Cancellation point Yes
Interrupt handler No
Signal handler Yes
Thread Yes

See also:

spawn(), wait(), wait3(), wait4(), waitid()

Processes and Threads chapter of Getting Started with QNX Neutrino