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<setjmp.h>: Non-local goto(3avr) avr-libc <setjmp.h>: Non-local goto(3avr)

NAME

<setjmp.h>: Non-local goto -

Functions


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.
Note:
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.
Example: 
#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.
Note:
longjmp() cannot cause 0 to be returned. If longjmp() is invoked with a second argument of 0, 1 will be returned instead.
Parameters:
__jmpb Information saved by a previous call to setjmp().
 
__ret Value to return to the caller of setjmp().
Returns:
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.
Parameters:
__jmpb Variable of type jmp_buf which holds the stack information such that the environment can be restored.
Returns:
setjmp() returns 0 if returning directly, and non-zero when returning from longjmp() using the saved context.

Author

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Wed Jun 4 2014 Version 1.8.0svn