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What is signal handling?
- Signals are the interrupts which force the operating system to stop the ongoing tasks and attend the task for which the interrupt has been sent.
- These interrupt can pause a service in any program of an operating system. In C++, various signals are offered which can catch and process in a program.
- The programmers can generate interrupts by pressing Ctrl+C on a LINUX, UNIX, Windows or Mac OS X. Some of the signals cannot be caught by the program but there is a following list of signals which you can catch in your program and can take proper actions based on the signal.
The <csignal> header file is used to define these signals.
SIGINT:
It produces receipt for an active signal.
SIGABRT:
It terminates the program abnormally.
SIGTERM:
It sends a termination request to the program.
SIGFPE:
It produces the erroneous arithmetic operation such as divide by zero or an operation resulting in an overflow.
SIGSEGV:
It means an invalid access to storage.
SIGILL:
This signal detects the illegal command or instruction.
The signal ( ) Function
In C++, signal handling library provides function signal to trap unexpected events.
Syntax for this function is:
signal(registered signal, signal handler)
- In the above syntax, the first argument is an integer which represents the signal number and the second argument is the pointer to a signal handling function.
- The signal which we want to be catching it should be registered and must be associated with a signal handling function. It should be of void type.
Let us have a look at the example:
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#include <iostream> #include <csignal> using namespace std; void signal_handler( int signalnum ) { cout << "The interrupt signal is (" << signalnum << "). \n"; // terminate program exit(signalnum); } int main () { signal(SIGABRT, signal_handler); // register signal SIGABRT and signal handler while(true) cout << "Hello World..." << endl; return 0; } |
To interrupt in between the program press Ctrl+C.
The raise( ) Function
In C++, the raise( ) function is used to generate signals. It takes integer signal number as an argument.
Syntax for the following is:
raise(signal sig);
In the above syntax, sig is the signal number which is used to send any of the signals: SIGABRT, SIGINT, SIGTERM, SIGSEGV, SIGILL, SIGHUP, SIGFPE.
Let us have a look at the example:
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#include <iostream> #include <csignal> using namespace std; void signal_handler( int signalnum ) { cout << "Interrupt signal is (" << signalnum << ").\n"; // terminate program exit(signalnum); } int main () { int count = 0; signal(SIGSEGV, signal_handler); // register signal SIGSEGV and signal handler while(++count) { cout << "Hello World..." << endl; if( count == 10 ) raise(SIGSEGV); } return 0; } |