() — Coherent 3.1.0


setjmp()                 General Function                setjmp()




Perform non-local goto

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

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,
setjmp helps to  provide a non-local goto facility.  setjmp saves
a stack  context in env, and returns value  zero.  The stack con-
text can be restored  with the function longjmp.  The type decla-
ration for  jmp_buf is in the header  file setjmp.h.  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.



































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