# <signal.h>

**[<signal.h>](https://en.cppreference.com/w/c/header/signal)** provides signal handling for asynchronous events: SIGINT (Ctrl+C), SIGTERM, SIGSEGV, etc. Register a handler with `signal(SIGNUM, handler)`. Handlers run asynchronously and can only safely call async-signal-safe functions like `write` and `_exit`.

The standard pattern is to set a flag in the handler and check it in the main loop.

## Example

This example catches SIGINT by setting a flag that the main loop polls.

```c
// compile: gcc -o signalexample signalexample.c
// run: ./signalexample (press Ctrl+C)
// description: signal handler that sets a flag for clean shutdown

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

volatile sig_atomic_t stop = 0;

void handler(int sig) {
    stop = 1;
}

int main() {
    signal(SIGINT, handler);
    puts("running... press Ctrl+C to stop");
    
    while (!stop) {
        putchar('.');
        fflush(stdout);
        sleep(1);
    }
    
    puts("\nshutting down cleanly");
    return 0;
}
```