SIG_DFL, SIG_IGN

< c‎ | program
Defined in header <signal.h>
#define SIG_DFL /*implementation defined*/
#define SIG_IGN /*implementation defined*/

The SIG_DFL and SIG_IGN macros expand into integral expressions that are not equal to an address of any function. The macros define signal handling strategies for signal() function.

Constant Explanation
SIG_DFL default signal handling
SIG_IGN signal is ignored

Example

#include <signal.h>
#include <stdio.h>
 
int main(void)
{
    /* using the default signal handler */
    raise(SIGTERM);
    printf("Exit main()\n");   /* never reached */
}

Output:

(none)

Example

#include <signal.h>
#include <stdio.h>
 
int main(void)
{
    /* ignoring the signal */
    signal(SIGTERM, SIG_IGN);
    raise(SIGTERM);
    printf("Exit main()\n");
}

Output:

Exit main()

References

  • C17 standard (ISO/IEC 9899:2018):
  • 7.14/3 Signal handling <signal.h> (p: 193)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.14/3 Signal handling <signal.h> (p: 265)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.14/3 Signal handling <signal.h> (p: 246)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • 4.7 SIGNAL HANDLING <signal.h>

See also