WSTOPSIG

WSTOPSIG is a macro defined in the POSIX C standard library header sys/wait.h. It is used to obtain the signal number that caused a child process to stop, as reported by wait or waitpid when the child is in a stopped state.

Use and behavior: WSTOPSIG(status) should be used only when WIFSTOPPED(status) returns true. In that case, WSTOPSIG(status) yields the signal number that halted the child. This information is helpful for debuggers, job control, or process-tracing scenarios where a process has been stopped by a signal rather than exited or being signaled to terminate.

Typical context: A parent process may invoke waitpid with options such as WUNTRACED to be notified when a child stops. If the child stops, WIFSTOPPED(status) is true and WSTOPSIG(status) returns the specific signal that caused the stop (for example, a stop signal like SIGSTOP, SIGTSTP, or a signal such as SIGTRAP in debugging with ptrace). The exact signal depends on how the stop occurred.

Portability: WSTOPSIG is part of the POSIX wait/waitpid interface and is supported on POSIX-compatible systems, including Linux, macOS, and BSD variants. It is intended to be used together with other macros such as WIFEXITED, WIFSIGNALED, WIFCONTINUED, and WEXITSTATUS to interpret the status value returned by waitpid.

See also: WIFSTOPPED, WIFEXITED, WIFSIGNALED, WCONTINUED, WEXITSTATUS, WTERMSIG.