C signal handling: Difference between revisions

Revision as of 01:27, 22 March 2022

Revision as of 00:19, 3 July 2022

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{{see also|Unix signal}}

The C standard defines only 6 signals. They are all defined in <code>signal.h</code> header (<code>csignal</code> header in [[C++]]):<ref name=c99>{{cite book | url=httphttps://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf | title=ISO/IEC 9899:1999 specification | at=p. 258, § 7.14 ''Signal handling''}}</ref>

*<code>SIGABRT</code> - "abort", abnormal termination.

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*<code>SIGTERM</code> - "terminate", termination request sent to the program.

Additional signals may be specified in the <code>signal.h</code> header by the implementation. For example, Unix and [[Unix-like]] operating systems (such as [[Linux]]) define more than 15 additional signals; see [[Unix signal]].<ref name="sus">{{cite web | url=httphttps://pubs.opengroup.org/onlinepubs/007904975/ | title=The Open Group Base Specifications Issue 6 - signal.h - signals | accessdate=10 January 2012}}</ref>

=== Debugging ===

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A signal handler is a [[Function (computer science)|function]] which is called by the target environment when the corresponding signal occurs. The target environment suspends execution of the program until the signal handler returns or calls <code>longjmp()</code>.

Signal handlers can be set with <code>signal()</code> or <code>sigaction()</code>. The behavior of <code>signal()</code> has been changed multiple times across history and is now considered deprecated.<ref>httphttps://man7.org/linux/man-pages/man2/signal.2.html Signal(2) manpage</ref> It is only portable when used to set a signal's disposition to SIG_DFL or SIG_IGN. Signal handlers can be specified for all but two signals ([[SIGKILL]] and [[SIGSTOP]] cannot be caught, blocked or ignored).

If the signal reports an error within the program (and the signal is not asynchronous), the signal handler can terminate by calling <code>abort()</code>, <code>exit()</code>, or <code>longjmp()</code>.

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! Description

|-

| {{anchor|raise}}<code>[httphttps://en.cppreference.com/w/c/program/raise raise]</code>

| artificially sends a signal to the calling process

|-

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|artificially sends a signal to a specified process

|-

| {{anchor|signal}}<code>[httphttps://en.cppreference.com/w/c/program/signal signal]</code>

| sets the action taken when the program receives a specific signal

|}