Sets up one of several ways for a thread to handle an interrupt signal from the OS.

#include <signal.h>

void (*signal (int sig, void (*func)(int sig [,int subcode]))) (int sig);

Parameters

sig

Signal value. Must be one of the manifest constants defined in SIGNAL.H.

func

Specifies what action is taken. Must be either a function address or one of the manifest constants defined in SIGNAL.H.

subcode

Optional subcode to the signal number.

Remarks

This function is implemented in the shared C library interface library (not in the shared C library), and is private to each application.

The sig argument must be one of these manifest constants:

The func must be either a function address or one of these manifest constants:

For all signals except SIGFPE and SIGUSRx, the function is passed the sig argument and executed.

For SIGFPE, the function pointed to by func is passed two arguments, SIGFPE and an integer error subcode, FPE_xxx; then the function is executed. The value of func is not reset upon receiving the signal. To recover from floating-point exceptions, use setjmp in conjunction with longjmp. If the function returns, the calling thread resumes execution with the floating-point state of the process left undefined.

If the function returns, the calling thread resumes execution immediately following the point at which it received the interrupt signal. This is true regardless of the type of signal or operating mode.

Before the specified function is executed, the value of func is set to SIG_DFL. The next interrupt signal is treated as described above for SIG_DFL, unless an intervening call to signal specifies otherwise. This allows the program to reset signals in the called function.

Since signal-handler routines are normally called asynchronously when an interrupt occurs, it is possible that your signal-handler function will assume control when an operation is incomplete and in an unknown state. Certain restrictions therefore apply to the C functions used in your signal-handler routine:

• Do not issue low-level or standard I/O functions, for example, printf, read, write, and fread.
• Do not call heap routines or any function that uses the heap routines, for example, malloc, strdup, or putenv.
• Do not use longjmp.

Return Values

The previous value of func. For example, if the previous value of func was SIG_IGN, the return value will be SIG_IGN.

Success.

-1 such as invalid sig or func values, and the function sets errno to EINVAL.

Failure.

Requirements

See Also

_exit, abort, fread, longjmp, malloc, putenv printf, raise, read, setjmp, strdup, write