SIG_DFL, SIG_IGN
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <csignal> | ||
| #define SIG_DFL /*implementation defined*/ | ||
| #define SIG_IGN /*implementation defined*/ | ||
The SIG_DFL and SIG_IGN macros expand into integral expressions that are not equal to an address of any function. The macros define signal handling strategies for std::signal() function.
| Constant | Explanation | 
| SIG_DFL | default signal handling | 
| SIG_IGN | signal is ignored | 
[edit] See also
| C documentation for SIG_DFL, SIG_IGN | 


