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setjmp(3)
NAME
  setjmp, _setjmp, longjmp, _longjmp - Save and restores the current
  execution context

SYNOPSIS
  #include <setjmp.h>

  int setjmp(
	  jmp_buf environment );

  void longjmp(
	  jmp_buf environment,
	  int value );

  int _setjmp(
	  jmp_buf environment );

  void _longjmp(
	  jmp_buf environment,
	  int value );

LIBRARY
  Standard C Library (libc)

  System V Library (libsys5.a, libsys5.so)

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  setjmp(), longjmp(): XSH4.2

  _setjmp(), _longjmp(): XSH4.2

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  environment
      Specifies an address for a jmp_buf structure.

  value
      Specifies the value you want written to the execution context as the
      return value of the setjmp() or _setjmp() function. If you specify 0
      (zero) in this parameter, the execution context contains a value of 1
      as the setjmp() or _setjmp() return value.  See the RETURN VALUES
      section for more information.

DESCRIPTION
  The setjmp() and longjmp() functions are useful when handling errors and
  interrupts encountered in low-level functions of a program.

  The setjmp() function saves the current stack context and signal mask in
  the buffer specified by the environment parameter. You then use the buffer
  in a later call to the longjmp() function. The longjmp() function restores
  the stack context and signal mask that were saved by the setjmp() function.

  After the longjmp() function runs, program execution continues as though
  the corresponding call to the setjmp() function had just returned the value
  of the value parameter.  The function that called the setjmp() function
  must not have returned before the completion of the longjmp() function.

  The _setjmp() and _longjmp() functions operate identically to the setjmp()
  and longjmp() functions, respectively, except that _setjmp() and _longjmp()
  manipulate only the stack context. These functions do not restore the
  signal mask.

  All accessible objects have values at the time longjmp() is called, except
  for some objects of automatic storage duration. Objects of automatic
  storage duration will have indeterminant values if they meet all of the
  following conditions:

  -   They are local to the function containing the corresponding setjmp()
      invocation.

  -   They do not have volatile-qualified type.

  -   They are changed between the setjmp() and the longjmp() call.

  Because it bypasses the usual function call and return mechanisms, the
  longjmp() function executes correctly in contexts of interrupts, signals,
  and any of their associated functions. However, if the longjmp() function
  is invoked from a nested signal handler (that is, from a function invoked
  as a result of a signal raised during the handling of another signal), the
  behavior is undefined.

NOTES
  [Tru64 UNIX]	For compatibility, the System V versions of the setjmp() and
  longjmp() functions, which are equivalent to _setjmp() and _longjmp(),
  respectively, are also supported. To use the System V versions of setjmp()
  and longjmp(), you must link with the libsys5 library before you link with
  libc.

RETURN VALUES
  After the longjmp() function is finished executing, program execution
  continues as though the corresponding call of the setjmp() function just
  returned. In other words, the execution context saved by the corresponding
  setjmp() function is in place and execution continues at the statement
  immediately following the call to the setjmp() function.

  Part of that execution context is the return value from the setjmp()
  function. When the setjmp() function actually returns (before the call to
  the longjmp() function), that return value is 0 (zero). When the longjmp()
  function returns, the execution context contains a non-zero value as the
  return value from the setjmp() function.

  The value you specify in the value parameter to the longjmp() function is
  written to the execution context as the return value for the setjmp()
  function. You cannot cause the execution context to contain a 0 (zero)
  value for the setjmp() return value. If you specify 0 in the value
  parameter, the execution context contains a 1 as the setjmp() return value.

CAUTION
  The results of the longjmp() function are undefined in the following
  situations:

    ·  The longjmp() function is called with an environment parameter that
       was not previously set by the setjmp() function.

    ·  The function that made the corresponding call to the setjmp() function
       has already returned.

  If the longjmp() function detects one of these conditions, it calls the
  longjmperror() function. If longjmperror() returns, the program is aborted.
  The default version of longjmperror() displays an error message to standard
  error and returns.  If you want your program to exit more gracefully, you
  can write your own version of the longjmperror() program.

SEE ALSO
  Routines: siglongjmp(3), sigsetjmp(3)

  Standards: standards(5)

Index for Section 3

Alphabetical listing for S

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