C in a Nutshell

Name

setjmp

Synopsis

Saves the calling environment as a long jump destination

#include <setjmp.h>
intsetjmp( jmp_buf env );

The setjmp() macro saves the current environment at the time of the call in a buffer specified by its argument. The environment includes the stack, and with it all variables that have automatic storage duration. Like the setjmp() macro itself, the argument’s type, jmp_buf, is defined in the header file setjmp.h.

A later call to the longjmp() function restores the saved environment. As a result, the longjmp() function does not return, but instead causes execution to continue as if control had returned from the setjmp(). However, while the original setjmp() call always returns 0, the apparent return value after longjmp() is never equal to zero.

Because the execution environment saved may not include other partial expressions, the return value of setjmp() must not be used except in simple conditional expressions, or in comparison to an integer constant value. Furthermore, if any variables with automatic storage duration in the function that called setjmp() were modified after the setjmp() call (and were not declared as volatile), then their values after the longjmp() call are indeterminate.

Example

This example shows the complete contents of two source files to illustrate how setjmp() and longjmp() allow you to escape from a function call.

#include <stdlib.h> #include <stdio.h> #include <setjmp.h> #include <errno.h> double calculate1( double x); // Functions defined double ...