signal.c

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2022.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU Lesser General Public License as published   *
* by the Free Software Foundation, either version 3 or (at your option)   *
* any later version. This program is distributed without any warranty.    *
* See the files COPYING.lgpl-v3 and COPYING.gpl-v3 for details.           *
\*************************************************************************/

/* Listing 22-1 */

#include <signal.h>

typedef void (*sighandler_t)(int);

sighandler_t
signal(int sig, sighandler_t handler)
{
    struct sigaction newDisp, prevDisp;

    newDisp.sa_handler = handler;
    sigemptyset(&newDisp.sa_mask);
#ifdef OLD_SIGNAL
    newDisp.sa_flags = SA_RESETHAND | SA_NODEFER;
#else
    newDisp.sa_flags = SA_RESTART;
#endif

    if (sigaction(sig, &newDisp, &prevDisp) == -1)
        return SIG_ERR;
    else
        return prevDisp.sa_handler;
}