In C programming, the raise() function is defined in the signal.h header file, and is used to send a signal to the current process or thread. The raise() function takes a single argument, which is an integer representing the signal to be raised.

The syntax for using the raise() function is:

#include <signal.h>

int raise(int sig);

The sig parameter specifies the signal to be raised, which can be any of the standard signals defined in the signal.h header file, such as SIGINT (interrupt signal) or SIGTERM (termination signal).

If the raise() function is called with a valid signal number, it will cause the specified signal to be sent to the current process or thread. The behavior of the process or thread in response to the signal depends on the signal itself and the signal handling mechanisms employed by the process or thread.

The return value of the raise() function is 0 if the signal was successfully sent, and -1 if an error occurred. Possible errors include sending a signal to a process or thread that does not exist or does not have permission to receive the signal.