<csignal>
void (*signal(int sig, void (*func)(int)))(int);
Set function to handle signal
Specifies a way to handle those signals with the signal number specified by sig.
There are three ways in which a signal can be handled by a program (which is specified by parameter func):
- Default handling (SIG_DFL): The signal is handled by the default action for that particular signal.
- Ignore signal (SIG_IGN): The signal is ignored and the code execution will continue even if unmeaningful.
- Function handler: A specific function is defined to handle the signal.
A specific compiler implementation may set either SIG_DFL or SIG_IGN as the default signal handling behavior for each of the supported signals at program startup.
Parameters
- sig
- The signal number to which a handling function is set. The following macro constant expressions identify standard signal numbers:
| macro | signal |
|---|
| SIGABRT | (Signal Abort) Abnormal termination, such as is initiated by the abort function. |
| SIGFPE | (Signal Floating-Point Exception) Erroneous arithmetic operation, such as zero divide or an operation resulting in overflow (not necessarily with a floating-point operation). |
| SIGILL | (Signal Illegal Instruction) Invalid function image, such as an illegal instruction. This is generally due to a corruption in the code or to an attempt to execute data. |
| SIGINT | (Signal Interrupt) Interactive attention signal. Generally generated by the application user. |
| SIGSEGV | (Signal Segmentation Violation) Invalid access to storage: When a program tries to read or write outside the memory it is allocated for it. |
| SIGTERM | (Signal Terminate) Termination request sent to program. |
Each compiler implentation may provide additional signal number macro constants to be used by this function.
Notice that not all running environments are required to generate automatic signals, not even in the specific cases described above, although all running environments must deliver signals generated by a explicit call to the raise function.
- func
- A pointer to a function. This may either be a function defined by the programmer or one of the following predefined functions:
| SIG_DFL | Default handling: The signal is handled by the default action for that particular signal. |
| SIG_IGN | Ignore Signal: The signal is ignored. |
If a function, it should follow the following prototype:
void handler_function ( int parameter );
Return value
The return type is the same as for parameter func.
If the request is successful, the function returns a pointer to the particular handler function in charge of handling this signal before the call, if any. Or SIG_DFL or SIG_IGN if before the call the signal was being handled by the default handler or was being ignored.
If the function was not successful in registering the new signal handling procedure, it returns SIG_ERR and sets errno to a positive value.
Example
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/* signal example */
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
char tmpfilename [L_tmpnam];
void terminate (int param)
{
printf ("Terminating program...\n");
remove (tmpfilename);
exit(1);
}
int main ()
{
void (*prev_fn)(int);
prev_fn = signal (SIGTERM,terminate);
if (prev_fn==SIG_IGN) signal (SIGTERM,SIG_IGN);
tmpnam (tmpfilename);
/* code here */
return 0;
}
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This program defines a terminate function that removes a previously created temporal file. This function is associated using signal to the SIGTERM signal, except if this signal was being ignored, in which case it is reset to SIG_IGN so that behavior remains unchanged.
See also
| raise | Generates a signal (function) |
|