SAS/C Library Reference, Vol. 1

onjmpout -- Intercept Nonlocal gotos

SYNOPSIS

 #include <lcjmp.h>

 void onjmpout(jmp_buf env, int code, target);

DESCRIPTION

onjmpout requests interception of calls to longjmp that could terminate the calling function. If a call to longjmp is later intercepted, control is passed to the target label. The env and code variables are modified to indicate the target and code specified by the intercepted longjmp so that it can be reissued by the intercepting routine.

onjmpout sets the code variable to 0 on completion. Because interception of a jump assigns the code variable a value other than 0, it can be tested elsewhere to determine whether interception has taken place.

After a call to longjmp is intercepted, onjmpout must be reissued if you want continued interception.

Because exit is implemented as a longjmp to the caller of main, you use onjmpout to intercept program exit.

RETURN VALUE

onjmpout has no return value.

CAUTION

Variables of storage class auto and register, whose values are changed between the onjmpout and longjmp calls, have indeterminate values after the branch to target unless declared volatile.

onjmpout is implemented as a macro and should not be used in any position where a value is required.

IMPLEMENTATION

onjmpout is implemented as

 #define onjmpout(e, c, t) if (c = blkjmp(e)) goto t

EXAMPLE

The following code fragment illustrates the use of onjmpout:

  #include <lcjmp.h>

  jmp_buf env;
  int jmpcode;

     /* Intercept abnormal exits.                      */
  onjmpout(env, jmpcode, cleanup);
  .
  .
  .
  cleanup:   /* Clean up after attempted exit.         */
  .
  .
  .
  longjmp(env, jmpcode); /* And then reissue the jump. */

RELATED FUNCTIONS

blkjmp, longjmp