Advanced Programming in the UNIX Environment by W. Richard Stevens states:

"What are the the states of the automatic variables and register variables in the main function?"

with regard to what happens when you longjmp back to main (or another function) from somewhere lower down the stack.

It goes on to say:

"It depends. Most implementations do not try to roll back these automatic variables and register variables, but all that the standards say is that their values are indeterminate. If you have an automatic variable that you don't want rolled back, define it with the volatile attribute. Variables that are declared global or static are left alone when longjmp is executed.

It seems like he's saying that normal stack-variables will not have their values set back to what they were at the time of the setjmp - but then the rest of the function couldn't rely on its stack variables after the longjmp back to it which seems crazy, so I'm guessing I'm wrong.

Can someone define "automatic variables" for me and explain what specifically isn't set back to its original value and why that is?

c unix
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