man3/longjmp.3

   1 .\" Written by Michael Haardt, Fri Nov 25 14:51:42 MET 1994
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  22 .\" Added siglongjmp, Sun Mar  2 22:03:05 EST 1997, jrv@vanzandt.mv.com
  23 .\" Modifications, Sun Feb 26 14:39:45 1995, faith@cs.unc.edu
  24 .\" "
  25 .TH LONGJMP 3 2009-01-13 "" "Linux Programmer's Manual"
  26 .SH NAME
  27 longjmp, siglongjmp \- nonlocal jump to a saved stack context
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <setjmp.h>
  31
  32 .BI "void longjmp(jmp_buf " env ", int " val );
  33
  34 .BI "void siglongjmp(sigjmp_buf " env ", int " val );
  35 .fi
  36 .sp
  37 .in -4n
  38 Feature Test Macro Requirements for glibc (see
  39 .BR feature_test_macros (7)):
  40 .in
  41 .sp
  42 .BR siglongjmp ():
  43 _POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _POSIX_C_SOURCE
  44 .SH DESCRIPTION
  45 .BR longjmp ()
  46 and
  47 .BR setjmp (3)
  48 are useful for dealing with errors
  49 and interrupts encountered in a low-level subroutine of a program.
  50 .BR longjmp ()
  51 restores the environment saved by the last call of
  52 .BR setjmp (3)
  53 with the corresponding \fIenv\fP argument.
  54 After
  55 .BR longjmp ()
  56 is completed, program execution continues as if the
  57 corresponding call of
  58 .BR setjmp (3)
  59 had just returned the value
  60 \fIval\fP.
  61 .BR longjmp ()
  62 cannot cause 0 to be returned.
  63 If
  64 .BR longjmp ()
  65 is invoked with a second argument of 0, 1 will be returned instead.
  66 .P
  67 .BR siglongjmp ()
  68 is similar to
  69 .BR longjmp ()
  70 except for the type of
  71 its \fIenv\fP argument.
  72 If, and only if, the
  73 .BR sigsetjmp (3)
  74 call that set this
  75 \fIenv\fP used a nonzero \fIsavesigs\fP flag,
  76 .BR siglongjmp ()
  77 also restores the signal mask that was saved by
  78 .BR sigsetjmp (3).
  79 .SH RETURN VALUE
  80 These functions never return.
  81 .SH CONFORMING TO
  82 C89, C99, and POSIX.1-2001 specify
  83 .BR longjmp ().
  84 POSIX.1-2001 specifies
  85 .BR siglongjmp ().
  86 .SH NOTES
  87 POSIX does not specify whether
  88 .BR longjmp ()
  89 will restore the signal context (see
  90 .BR setjmp (3)
  91 for some more details).
  92 If you want to portably save and restore signal masks, use
  93 .BR sigsetjmp (3)
  94 and
  95 .BR siglongjmp ().
  96 .P
  97 The values of automatic variables are unspecified after a call to
  98 .BR longjmp ()
  99 if they meet all the following criteria:
 100 .IP \(bu 3
 101 they are local to the function that made the corresponding
 102 .BR setjmp (3)
 103 call;
 104 .IP \(bu
 105 their values are changed between the calls to
 106 .BR setjmp (3)
 107 and
 108 .BR longjmp ();
 109 and
 110 .IP \(bu
 111 they are not declared as
 112 .IR volatile .
 113 .P
 114 Analogous remarks apply for
 115 .BR siglongjmp ().
 116 .P
 117 .BR longjmp ()
 118 and
 119 .BR siglongjmp ()
 120 make programs hard to
 121 understand and maintain.
 122 If possible an alternative should be used.
 123 .SH SEE ALSO
 124 .BR setjmp (3),
 125 .BR sigsetjmp (3)