Why Linux always output “^C” upon pressing of Ctrl+C?

Question

I have been studying signals in Linux. And I\'ve done a test program to capture SIGINT.

#include 
#include 
#include 

        

Answer 1

The shell echoes everything you type, so when you type ^C, that too gets echoed (and in your case intercepted by your signal handler). The command stty -echo may or may not be useful to you depending on your needs/constraints, see the man page for stty for more information.

Of course much more goes on at a lower level, anytime you communicate with a system via peripherals device drivers (such as the keyboard driver that you use to generate the ^C signal, and the terminal driver that displays everything) are involved. You can dig even deeper at the level of assembly/machine language, registers, lookup tables etc. If you want a more detailed, in-depth level of understanding the books below are a good place to start:

The Design of the Unix OS is a good reference for these sort of things. Two more classic references: Unix Programming Environment and Advanced Programming in the UNIX Environment

Nice summary here in this SO question How does Ctrl-C terminate a child process?

"when youre run a program, for example find, the shell:

• the shell fork itself
• and for the child set the default signal handling
• replace the child with the given command (e.g. with find)
• when you press CTRL-C, parent shell handle this signal but the child will receive it - with the default action - terminate. (the child can implement signal handling too)"