SIG_DFL, SIG_IGN

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C
 
Program support utilities
Program termination
Communicating with the environment
Signals
SIG_DFLSIG_IGN
Signal types
Non-local jumps
Types
 
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

Run this code
#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

Run this code
#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

  • 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