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setjmp

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. .PP

  #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. .PP

  #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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