A handler declared as `void signal_handler(int sig)` receives a signal number in `sig`. The number identifies the kind of signal; named constants from `signal.h` let the handler distinguish them without relying on particular numeric values. section 17.6
C defines six standard signal numbers:
- `SIGFPE`: erroneous arithmetic operation; `SIGILL`: invalid instruction; `SIGSEGV`: invalid access to storage. section 17.6
- `SIGABRT`: abnormal termination; `SIGINT`: interactive attention signal; `SIGTERM`: termination request. section 17.6
143 /**
144 ** @brief A minimal signal handler
145 **
146 ** After updating the signal count, for most signals this
147 ** simply stores the signal value in "interrupt" and returns.
148 **/
149 static void signal_handler(int sig) {
150 sh_count(sig);
151 switch (sig) {
152 case SIGTERM: quick_exit(EXIT_FAILURE);
153 case SIGABRT: _Exit(EXIT_FAILURE);
154 #ifdef SIGCONT
155 // continue normal operation
156 case SIGCONT: return;
157 #endif
158 default:
159 /* reset the handling to its default */
160 signal(sig, SIG_DFL);
161 interrupt = sig;
162 return;
163 }
164 }
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In the handler, `switch (sig)` selects actions for `SIGTERM` and `SIGABRT`. The default case passes the same number to `signal(sig, SIG_DFL)` to restore its default handling. section 17.6
TAKEAWAY: A signal number identifies a signal, not how it must be handled. Platforms may define additional `SIG` names, but their meaning comes from the platform rather than the C standard; using them reduces portability. section 17.6
