SIG_DFL, SIG_IGN

 

C

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Technical Specifications

Symbol index

 

Program support utilities

Program termination
abort exit quick_exit (C11) _Exit (C99)	atexit at_quick_exit (C11) EXIT_SUCCESSEXIT_FAILURE
Unreachable control flow
unreachable (C23)
Communicating with the environment
system	getenvgetenv_s (C11)
Signals
signal raise sig_atomic_t	SIG_DFLSIG_IGN SIG_ERR
Signal types
SIGABRTSIGFPESIGILL	SIGINTSIGSEGVSIGTERM
Non-local jumps
setjmp	longjmp
Types
jmp_buf

 

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

• 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>