# <setjmp.h>

<head><title>&lt;setjmp.h&gt;</title></head>

# `<setjmp.h>`

* * *

Include the standard header **`<setjmp.h>`**
to perform control transfers that bypass
the normal function call and return protocol.

    #define setjmp(jmp_buf env) <int rvalue>
    
    typedef a-type jmp_buf;
    void longjmp(jmp_buf env, int val);Copy to clipboard

## `jmp_buf`

    typedef a-type jmp_buf;Copy to clipboard

The type is the array type `a-type` of an object that
you declare to hold the context information stored by
[`setjmp`](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_setjmp.html#setjmp) and accessed by
[`longjmp`](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_setjmp.html#longjmp).

## `longjmp`

    void longjmp(jmp_buf env, int val);Copy to clipboard

The function causes a second return from the execution of
[`setjmp`](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_setjmp.html#setjmp)
that stored the current context value in `env`.
If `val` is nonzero, the return value is `val`;
otherwise, it is 1.

The function that was active when
[`setjmp`](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_setjmp.html#setjmp) stored the current
context value must not have returned control to its caller. An object
with dynamic duration that does not have a *volatile* type and
whose stored value has changed since the current context value was stored
will have a stored value that is indeterminate.

## `setjmp`

    #define setjmp(jmp_buf env) <int rvalue>Copy to clipboard

The macro stores the current context value in the array
designated by `env` and returns zero. A later call to
[`longjmp`](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_setjmp.html#longjmp)
that accesses the same context value causes
`setjmp` to again return, this time with a nonzero value.
You can use the macro `setjmp` only in an expression that:

- has no operators
- has only the unary operator `!`
- has one of the relational or equality operators (`==`,
`!=`, `<`, `<=`,
`>`, or `>=`) with the other
operand an integer constant expression

You can write such an expression only as the *expression*
part of a
[*do*](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_function.html#Do%20Statement),
[*expression*](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_function.html#Expression%20Statement),
[*for*](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_function.html#For%20Statement),
[*if*](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_function.html#If%20Statement),
[*if-else*](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_function.html#If-Else%20Statement),
[*switch,*](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_function.html#Switch%20Statement), or
[*while*](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_function.html#While%20Statement) statement.

* * *

See also the
**[Table of Contents](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_index.html#Table%20of%20Contents)** and the
**[Index](https://docs.qualcomm.com/doc/80-N3040-23/topic/_c_index.html)**.

*[Copyright](https://docs.qualcomm.com/doc/80-N3040-23/topic/c_crit_pjp.html) © 1992-2006by P.J. Plauger and Jim Brodie. All rights reserved.*

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Last Published: Oct 06, 2026

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