NAME

longjmp - non-local goto

SYNOPSIS

#include <setjmp.h>

void longjmp(jmp_buf env, int val);


DESCRIPTION

^[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to the ISO C standard.

The longjmp() function shall restore the environment saved by the most recent invocation of setjmp() in the same thread, with the corresponding jmp_buf argument. If there is no such invocation, or if the function containing the invocation of setjmp() has terminated execution in the interim, or if the invocation of setjmp() was within the scope of an identifier with variably modified type and execution has left that scope in the interim, the behavior is undefined. ^[CX]  It is unspecified whether longjmp() restores the signal mask, leaves the signal mask unchanged, or restores it to its value at the time setjmp() was called.

All accessible objects have values, and all other components of the abstract machine have state (for example, floating-point status flags and open files), as of the time longjmp() was called, except that the values of objects of automatic storage duration are unspecified if they meet all 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() invocation and longjmp() call.

^[CX] As it bypasses the usual function call and return mechanisms, longjmp() shall execute correctly in contexts of interrupts, signals, and any of their associated functions. However, if longjmp() 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.

The effect of a call to longjmp() where initialization of the jmp_buf structure was not performed in the calling thread is undefined.

RETURN VALUE

After longjmp() is completed, program execution continues as if the corresponding invocation of setjmp() had just returned the value specified by val. The longjmp() function shall not cause setjmp() to return 0; if val is 0, setjmp() shall return 1.

ERRORS

No errors are defined.

EXAMPLES

None.

APPLICATION USAGE

Applications whose behavior depends on the value of the signal mask should not use longjmp() and setjmp(), since their effect on the signal mask is unspecified, but should instead use the siglongjmp() and sigsetjmp() functions (which can save and restore the signal mask under application control).

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

setjmp(), sigaction(), siglongjmp(), sigsetjmp(), the Base Definitions volume of IEEE Std 1003.1-2001, <setjmp.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

The DESCRIPTION is updated for alignment with the POSIX Threads Extension.

Issue 6

Extensions beyond the ISO C standard are marked.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

• The DESCRIPTION now explicitly makes longjmp()'s effect on the signal mask unspecified.

The DESCRIPTION is updated for alignment with the ISO/IEC 9899:1999 standard.