Introduction
If a programs causes any problem during execution, signals are sent and the operating system terminates the programs. The program does not rectify most of the error causing signals. But, single header file includes all these Signal Header file and precautions are applied as per the signal occurred. The header file to be included in C++ is
<csignal>.
The "CPP Signal Handler" clears the generated signals. It provides an alternative solution to the problem or terminates the entire program. Signals
| Signal | Description |
|---|---|
| SIGFPE | Error in mathematical calculations |
| SIGABRT | Terminates the program abnormally |
| SIGINT | Occurrence of interaction signal |
| SIGILL | Implies instruction given is illegal |
| SIGTERM | Request terminated |
| SIGSEGV | The storage accessed is invalid |
Syntax
void (*signal (int signal_name , type (*function)(data_type)))(data_type);
The above syntax implies a signal function with two arguments in which the
first argument is the number of signal and
second denotes the pointer to handler of signal occurred. Example
[c]
#include <iostream>
#include <csignal>
using namespace std;
void sig_handler( int signal_number )
{
cout << "Signal interrupt" << signal_number << " occurred" << endl;
//Terminates the program as signal occurred
exit(signal_number);
}
int main ()
{
// register signal SIGINT and signal handler
signal(SIGILL, sig_handler);
while(1)
{
cout << "Shutting down...!! " << endl;
}
return 0;
}[/c]
Output
[c]
Shutting down...!!
Shutting down...!!
Shutting down...!!
.
.
.
.
[/c]
Description
The other function called Raise can be used to create and implement these signals. It sends signal
sig to the current executing program. If none of the function handlers defines signal to handle the raised signal, the function never throws exceptions. Syntax
int raise (signal signal_number);
Example
[c]
#include <iostream>
#include <csignal>
using namespace std;
void sig_handler( int signal_number )
{
cout << "Signal interrupt" << signal_number << " has occured";
exit(signal_number);
}
int main ()
{
int x = 0;
// registration of signal SIGILL and signal handler
signal(SIGILL, sig_handler);
while(++x)
{
cout << "Shutting down...!!" << endl;
if( x == 10 )
{
raise( SIGINT);
}
}
return 0;
}[/c]
Output
[c]
Shutting down...!!
Shutting down...!!
Shutting down...!!
Shutting down...!!
Shutting down...!!
Shutting down...!!
Shutting down...!!
Shutting down...!!
Shutting down...!!
Shutting down...!![/c]
Key Points
- CPP Signal Handler can be used by placing <csignal> header file
- Raise function helps to create the error handling signals
Programming
Tips
The other way to abort the flow of program is to press Ctrl+C.
When these two keys are pressed, the proper Signal Handler is used to generate SIGNIT signal and abort.