1setjmp(3UCB) SunOS/BSD Compatibility Library Functions setjmp(3UCB)
2
6 setjmp, longjmp, _setjmp, _longjmp - non-local goto
7
9 /usr/ucb/cc [ flag ... ] file ...
10 #include <setjmp.h>
11 int setjmp(env)
13 jmp_buf env;
14 void longjmp(env, val)
17 jmp_buf env;
18 int val;
19 int _setjmp(env)
22 jmp_buf env;
23 void _longjmp(env, val)
26 jmp_buf env;
27 int val;
28
31 The setjmp() and longjmp() functions are useful for dealing with errors
32 and interrupts encountered in a low-level subroutine of a program.
33 The setjmp() function saves its stack environment in env for later use
36 by longjmp(). A normal call to setjmp() returns zero. setjmp() also
37 saves the register environment. If a longjmp() call will be made, the
38 routine which called setjmp() should not return until after the
39 longjmp() has returned control (see below).
40 The longjmp() function restores the environment saved by the last call
43 of setjmp(), and then returns in such a way that execution continues as
44 if the call of setjmp() had just returned the value val to the function
45 that invoked setjmp(); however, if val were zero, execution would con‐
46 tinue as if the call of setjmp() had returned one. This ensures that a
47 ``return'' from setjmp() caused by a call to longjmp() can be distin‐
48 guished from a regular return from setjmp(). The calling function must
49 not itself have returned in the interim, otherwise longjmp() will be
50 returning control to a possibly nonexistent environment. All memory-
51 bound data have values as of the time longjmp() was called. The CPU
52 and floating-point data registers are restored to the values they had
53 at the time that setjmp() was called. But, because the register stor‐
54 age class is only a hint to the C compiler, variables declared as reg‐
55 ister variables may not necessarily be assigned to machine registers,
56 so their values are unpredictable after a longjmp(). This is especially
57 a problem for programmers trying to write machine-independent C rou‐
58 tines.
59 The setjmp() and longjmp() functions save and restore the signal mask
62 while _setjmp() and _longjmp() manipulate only the C stack and regis‐
63 ters.
64 None of these functions save or restore any floating-point status or
67 control registers.
68
70 Example 1 Examples of setjmp() and longjmp().
71 The following example uses both setjmp() and longjmp() to return the
74 flow of control to the appropriate instruction block:
75 #include <stdio.h>
78 #include <setjmp.h>
79 #include <signal.h>
80 #include <unistd.h>
81 jmp_buf env; static void signal_handler();
82 main() {
83 int returned_from_longjump, processing = 1;
84 unsigned int time_interval = 4;
85 if ((returned_from_longjump = setjmp(env)) != 0)
86 switch (returned_from_longjump) {
87 case SIGINT:
88 printf("longjumped from interrupt %d\n",SIGINT);
89 break;
90 case SIGALRM:
91 printf("longjumped from alarm %d\n",SIGALRM);
92 break;
93 }
94 (void) signal(SIGINT, signal_handler);
95 (void) signal(SIGALRM, signal_handler);
96 alarm(time_interval);
97 while (processing) {
98 printf(" waiting for you to INTERRUPT (cntrl-C) ...\n");
99 sleep(1);
100 } /* end while forever loop */
101 }
102 static void signal_handler(sig)
104 int sig; {
105 switch (sig) {
106 case SIGINT: ... /* process for interrupt */
107 longjmp(env,sig);
108 /* break never reached */
109 case SIGALRM: ... /* process for alarm */
110 longjmp(env,sig);
111 /* break never reached */
112 default: exit(sig);
113 }
114 }
115 When this example is compiled and executed, and the user sends an
119 interrupt signal, the output will be:
120 longjumped from interrupt
123 Additionally, every 4 seconds the alarm will expire, signalling this
127 process, and the output will be:
128 longjumped from alarm
131
134 sigvec(3UCB), setjmp(3C), signal(3C)
135
137 Use of these interfaces should be restricted to only applications writ‐
138 ten on BSD platforms. Use of these interfaces with any of the system
139 libraries or in multi-thread applications is unsupported.
140
142 The setjmp() function does not save the current notion of whether the
143 process is executing on the signal stack. The result is that a
144 longjmp() to some place on the signal stack leaves the signal stack
145 state incorrect.
146 On some systems setjmp() also saves the register environment. There‐
149 fore, all data that are bound to registers are restored to the values
150 they had at the time that setjmp() was called. All memory-bound data
151 have values as of the time longjmp() was called. However, because the
152 register storage class is only a hint to the C compiler, variables
153 declared as register variables may not necessarily be assigned to
154 machine registers, so their values are unpredictable after a longjmp().
155 When using compiler options that specify automatic register allocation,
156 the compiler will not attempt to assign variables to registers in rou‐
157 tines that call setjmp().
158 The longjmp() function never causes setjmp() to return 0, so program‐
161 mers should not depend on longjmp() being able to cause setjmp() to
162 return 0.
163SunOS 5.11 7 Apr 1993 setjmp(3UCB)