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setjmp()                 General Function                setjmp()




Perform non-local goto

#include <setjmp.h>
iinntt sseettjjmmpp(_e_n_v) jjmmpp_bbuuff _e_n_v;

The function call is the only mechanism that C provides to trans-
fer control  between functions.  This mechanism,  however, is in-
adequate for some purposes, such as handling unexpected errors or
interrupts at  lower levels of  a program.  To  answer this need,
sseettjjmmpp helps to  provide a non-local _g_o_t_o facility.  sseettjjmmpp saves
a stack  context in _e_n_v, and returns value  zero.  The stack con-
text can be restored  with the function longjmp.  The type decla-
ration for  jjmmpp_bbuuff is in the header  file sseettjjmmpp.hh.  The context
saved  includes the  program  counter, stack  pointer, and  stack
frame.

***** Example *****

The following gives a simple example of setjmp and longjmp.


#include <setjmp.h>



jmp_buf env;    /* place for setjmp to store its environment */



main()
{
        int rc;



        if(rc = setjmp(env)) { /* we come here on return */
                printf("First char was %c\n", rc);
                exit(0);
        }
        subfun();       /* this never returns */
}



subfun()
{
        char buf[80];









COHERENT Lexicon                                           Page 1




setjmp()                 General Function                setjmp()



        do {
                printf("Enter some data\n");
                gets(buf);      /* get data */
        } while(!buf[0]);       /* retry on null line */



        longjmp(env, buf[0]);   /* buf[0] must be non zero */
}


***** See Also *****

general functions, getenv(), longjmp()

***** Notes *****

Programmers should  note that many user-level  routines cannot be
interrupted and reentered  safely.  For that reason, improper use
of setjmp  and longjmp  can create mysterious  and irreproducible
bugs.  The  use of longjmp to exit  interrupt exception or signal
handlers is particularly hazardous.



































COHERENT Lexicon                                           Page 2

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