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setjmp(3avr) avr-libc setjmp(3avr)


setjmp - <setjmp.h>: Non-local goto



int setjmp (jmp_buf __jmpb)
void longjmp (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__

Detailed Description

While the C language has the dreaded goto statement, it can only be used to jump to a label in the same (local) function. In order to jump directly to another (non-local) function, the C library provides the setjmp() and longjmp() functions. setjmp() and longjmp() are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program.


setjmp() and longjmp() make programs hard to understand and maintain. If possible, an alternative should be used.

longjmp() can destroy changes made to global register variables (see How to permanently bind a variable to a register?).

For a very detailed discussion of setjmp()/longjmp(), see Chapter 7 of Advanced Programming in the UNIX Environment, by W. Richard Stevens.


#include <setjmp.h>
jmp_buf env;
int main (void)

if (setjmp (env))
... handle error ...
while (1)
... main processing loop which calls foo() some where ...
} } ... void foo (void) {
... blah, blah, blah ...
if (err)
longjmp (env, 1);
} }

Function Documentation

void longjmp (jmp_buf __jmpb, int __ret)

Non-local jump to a saved stack context.

#include <setjmp.h>

longjmp() restores the environment saved by the last call of setjmp() with the corresponding __jmpb argument. After longjmp() is completed, program execution continues as if the corresponding call of setjmp() had just returned the value __ret.


longjmp() cannot cause 0 to be returned. If longjmp() is invoked with a second argument of 0, 1 will be returned instead.


__jmpb Information saved by a previous call to setjmp().
__ret Value to return to the caller of setjmp().


This function never returns.

int setjmp (jmp_buf __jmpb)

Save stack context for non-local goto.

#include <setjmp.h>

setjmp() saves the stack context/environment in __jmpb for later use by longjmp(). The stack context will be invalidated if the function which called setjmp() returns.


__jmpb Variable of type jmp_buf which holds the stack information such that the environment can be restored.


setjmp() returns 0 if returning directly, and non-zero when returning from longjmp() using the saved context.


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Fri Jan 7 2022 Version 2.0.0