How to make child process die after parent exits?

Suppose I have a process which spawns exactly one child process. Now when the parent process exits for whatever reason (normally or abnormally, by kill, ^C, assert failure or anything else) I want the child process to die. How to do that correctly?

Some similar question on stackoverflow:

• (asked earlier) How can I cause a child process to exit when the parent does?
• (asked later) Are child processes created with fork() automatically killed when the parent is killed?

Some similar question on stackoverflow for Windows:

• How do I automatically destroy child processes in Windows?
• Kill child process when parent process is killed