wait

Suspends the calling process to wait for exit status of child processes.

Syntax

   #include <sys/types.h>

   #include <sys/wait.h>

   pid_t wait (int *stat_loc);

Parameters

stat_loc: A pointer to the exit status of the child process. No information is returned if stat_loc is NULL.

Return Values

>0: Success. The process ID of a child process that has terminated is returned.
-1: An error occurred. There is no result, and errno is set to indicate the error condition.

Description

The wait() function suspends the calling process until status information for one of its terminated child processes is available. If status information is already available, wait() returns immediately.

If the calling process receives a signal whose action is to terminate, the calling process terminates. If the calling process receives a signal whose action is to execute a signal handling function, wait() returns to the calling process.

If status is available for more than one process, the order in which their status is reported may not correspond to the order of their termination.

The wait() function returns to the argument pointed to by stat_loc an exit status of 0 if, and only if, the child process that returned status took one of the following two actions:

returned a value of zero from its main() function (outer block)
passed a status value of zero to _exit() or exit()

The following macros that evaluate the stat_loc parameter, regardless of its value, are defined in the header <sys/wait.h>:

WIFEXITED(exit_status): Evaluates to a nonzero value if status was returned for a child process that terminated normally.
WEXITSTATUS(exit_status): If WIFEXITED is nonzero, this macro evaluates to the low-order 8 bits of the stat_loc parameter that the child process passed to _exit() or exit(), or the value that the child process returned from main().
WIFSIGNALED(exit_status): Evaluates to a nonzero value if status was returned for a child process that terminated due to the receipt of a signal that was not caught.
WTERMSIG(exit_status): If WIFSIGNALED is nonzero, this macro evaluates to the number of the signal that caused the termination of the child process.
WIFSTOPPED(exit_status): Evaluates to a nonzero value if status was returned for a child process that is currently stopped.
WSTOPSIG(exit_status): If WIFSTOPPED is nonzero, this macro evaluates to the number of the signal that caused the child process to stop.

Implementation Considerations

Refer to the EFAULT error description below.

If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes are terminated.

Errors

If an error occurs, errno is set to one of the following values:

`ECHILD`	CAUSE	The calling process has no unwaited-for child processes.
	ACTION	No action is necessary.
`EFAULT`	CAUSE	The system detected a bad address in attempting to use the `stat_loc` parameter.
	ACTION	Make sure that the pointer is correctly initialized.
`EINTR`	CAUSE	The function was interrupted by a signal. The `stat_loc` parameter's value is undefined.
	ACTION	Call the `wait()` function again to continue waiting.

wait

Technical documentation

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