- Maps an signal number to an signal message string, the contents of
- which are implementation defined. On systems which have the external
- variable sys_siglist, these strings will be the same as the ones used
- by psignal().
-
- If the supplied signal number is within the valid range of indices
- for the sys_siglist, but no message is available for the particular
- signal number, then returns the string "Signal NUM", where NUM is the
- signal number.
-
- If the supplied signal number is not a valid index into sys_siglist,
- returns NULL.
-
- The returned string is only guaranteed to be valid only until the
- next call to strsignal.