signal - change the action for a signal
integer*4 function signal(signum, proc, flag) integer*4 signum, flag external proc
For 64-bit environments: integer*8 function signal(signum, proc, flag) integer*8 flag integer*4 signum external proc
When compiling for 64-bit environments, with compiler option -m64, proc, and flag must be declared integer*8 as well as any variables receiving the result from signal.
If a process incurs a signal (see signal(3C)), the default action is usually to clean up and abort. You can choose to write an alternative signal handling routine. A call to signal is the way this alternate action is specified to the system.
Input:
signum is the signal number (see signal.h(3HEAD)). proc is the name of a user signal handling routine. If flag is negative, then proc must be the name of the user signal handling routine. If flag is zero or positive, then proc is ignored and the value of flag is passed to the system as the signal action definition. In particular, this is how previously saved signal actions can be restored. Two possible values for flag have specific meanings:
0 means "use the default action." See NOTES below. 1 means "ignore this signal."
Output:
A positive returned value is the previous action definition. A value greater than 1 is the address of a routine that was to have been called on occurrence of the given signal. A negative returned value is the negation of a system error code. See perror(3F). The returned value can be used in subsequent calls to signal to restore a previous action definition.
libfsu.a, libfsu.so.
kill(1), kill(3F), perror(3F), signal(3C)
When a negative flag value is desired in a 64-bit environment, use the INTEGER*8 literal value -1_8 in the call to signal.
If the user signal handler is called, it is passed the signal number as an integer argument.
This function may fail if the code for a function passed to it as flag is loaded at addresses with the high bit set. This will be interpreted as a negative value for flag when the behavior for positive values is desired. This is less likely to happen in 64-bit environments, or with statically-linked code.
On Linux systems, the signal() man page is in man page section 2 and the signal numbers are in section 7.