Signal () function describes Linux functions in detail

http://blog.csdn.net/ta893115871/article/details/7475095

Signal () function describes Linux functions in detail

Signal () function understanding

In the <signal.h> header file.

Signal (parameter 1, parameter 2);

Parameter 1: The signal we are going to process. The signal of the system we can again terminal type Kill-l view (total 64). Actually these signals are the system-defined macros.

Parameter 2: How we handle it (whether the system is default or ignored or captured).

Generally, there are 3 ways to operate.

(1) eg:signal (SIGINT, sig_ing);

Sig_ing represents ignoring SIGINT signals, SIGINT signals are generated by Interruptkey, usually ctrl +c or delete. The process that is sent to all foreground group.

Here we write a dead loop:

Then we save the execution.

Press CTRL _c The program does not respond. That's right

If we want to end the program you can press CTRL +\ to end

Actually, when we press CTRL +\, the Sigquit signal is generated.

(2) eg:signal (SIGINT, SIG_DFL);

SIGINT signals are generated by Interruptkey, usually ctrl +c or delete. The process that is sent to all foregroundgroup. The SIG_DFL represents the system default action, which in fact terminates the process for most signals when the system default action is performed. This is the same as not writing this handler function.

We're going to change the procedure above

You can then press CTRL +C to terminate the process. Put signal (SIGINT,SIG_DFL); this sentence is removed, the effect is the same.

(3) void (*signal (int sig, void (* handler) (int))) (int);
Int (*p) ();
This is a function pointer, and p points to a function that has no arguments and returns a value of int.
Int (*fun ()) ();
The difference between this and the above is that the fun () instead of P, and fun () is a function, so it can be considered as fun () after the function is executed, its return value is a function pointer, the function pointer (in fact, the p above) is a function that points to no parameters, And a function that returns a value of int.

void (*signal (int signo, void (*handler))) (int)), which can be seen as a signal () function (which itself is a function with two parameters, an integer type, and a function pointer), and this signal () The return value of a function is also a function pointer, which points to a function with an integer parameter and a return value of void.

The function for signal processing when writing a signal processing function is also void sig_fun (int signo), which is exactly the same as the function pointer that is returned by the signal () function above. void (*signal ()) (int);

Signal is a function that returns a function pointer to a function that takes an integer parameter and does not return a value, looking closely at the 2nd argument of the siganal (int signo, void (*handler) (int)), and the fact that he is returning the S Ignal 2nd signal processing function, point to the signal processing function, you can execute the function (signal internal, signal the signal as a parameter to the handler signal processing function, and then signal function return pointer, and then point to the signal handler function, start to execute it)

So what about the parameters of the signal function? The signal function accepts two parameters: an integer signal number, and a pointer to a user-defined signal handler function. We have previously defined a pointer SFP that points to a user-defined signal handler function:

void (*SFP) (int);

The type of SFP can be obtained by removing the SFP from the above declaration, Void (*) (int). In addition, the return value of the signal function is a pointer to the user-defined signal handler function before the call, and the type of the pointer is consistent with the type of the SFP pointer. Therefore, we can declare the signal function as follows:

void (*signal (int, void (*) (int)))) (int);

Similarly, using typedef can simplify the function declaration above:

typedef void (*handler) (int); HANDLER signal (int, HANDLER);

Ok; Look at an example:

This program is for when we press the CTRL +C key, the signal handler function we define is executed.

The number of the signal is printed every time we press the CTRL +c key. It can be seen that the signal num is 2

To exit you can press CTRL +\ to print the result as the last line.

Some of the commonly used signal are as follows:

Note: The following is from the Baidu Library Search (*^__^*) hehe ...

Signal	Description
Sigabrt	Generated by calling the Abort function, the process is not properly exited
Sigalrm	A timer timeout or Setitimer function set with the alarm function sets the interval timer timeout
Sigbus	A specific hardware exception, usually caused by memory access
Sigcancel	Used internally by the Solaris Thread Library and typically does not use
SIGCHLD	When a process terminate or stops, SIGCHLD sends it to its parent process. By default, the signal is ignored
Sigcont	When the stop process resumes running, it is automatically sent
Sigemt	and implementation-related hardware exceptions
SIGFPE	Math-related anomalies, such as being removed by 0, floating-point overflow, etc.
Sigfreeze	Solaris dedicated, hiberate or suspended when sent
SIGHUP	Sent to controlling Process with terminal when terminal is disconnect
Sigill	Illegal instruction exception
Siginfo	BSD signal. Generated by status key, usually ctrl+t. Processes that are sent to all foreground group
SIGINT	Generated by interrupt key, usually CTRL + C or delete. Processes that are sent to all foreground group
SIGIO	Asynchronous IO Events
Sigiot	Implementation of related hardware exceptions, general correspondence SIGABRT
SIGKILL	cannot be processed and ignored. Abort a process
Siglwp	Used internally by the Solaris Thread Libray
Sigpipe	Sent when the pipe was written after reader abort
Sigpoll	Send when an event is sent to pollable device
Sigprof	Setitimer the specified profiling Interval timer is generated
Sigpwr	and system-related. and UPS-related.
Sigquit	When you enter Quit key (ctrl+\), the process is sent to all foreground group
SIGSEGV	Illegal memory access
Sigstkflt	Linux dedicated, math coprocessor stack exception
SIGSTOP	Aborts the process. cannot be processed and ignored.
Sigsys	Illegal system calls
SIGTERM	Request abort process, kill command sent by default
Sigthaw	Solaris dedicated, sent from suspend recovery time
SIGTRAP	Implements the associated hardware exception. debugging exceptions are generally
Sigtstp	Suspend Key, usually Ctrl + Z. Processes that are sent to all foreground group
Sigttin	Sent when background group's process attempts to read terminal
Sigttou	Sent when background group's process tries to write terminal
Sigurg	may be sent when Out-of-band data is received
SIGUSR1	User-definable signal 1
SIGUSR2	User-definable Signal 2
Sigvtalrm	Virtual Interval Timer Timeout when Setitimer function is set
Sigwaiting	Solaris Thread Library Internal Implementation-specific
Sigwinch	All processes sent to foreground group when the terminal's window size changes
Sigxcpu	When the CPU time limit expires
Sigxfsz	Process exceeds file size limit
Sigxres	Solaris dedicated, sending when process exceeds resource limit

Signal () function describes Linux functions in detail