---
name: "trampoline"
section: "3"
platform: "linux"
package: "ffcall"
version: "2.5-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/trampoline"
---

# trampoline(3)

closures as first-class C functions

## NAME

trampoline - closures as first-class C functions

## SYNOPSIS

**#include \<trampoline.h\>**

**function = alloc\_trampoline(address, variable, data);**

**free\_trampoline(function);**

```
is_trampoline(function)
trampoline_address(function)
trampoline_variable(function)
trampoline_data(function)
```

## DESCRIPTION

These functions implement *closures* as first-class C functions. A closure consists of a regular C function and a piece of data which gets passed to the C function when the closure is called.

Closures as *first-class C functions* means that they fit into a function pointer and can be called exactly like any other C function. *function* **= alloc\_trampoline(***address***,** *variable***,** *data***)** allocates a closure. When *function* gets called, it stores *data* in the variable *variable* and calls the C function at *address*. The function at *address* is responsible for fetching *data* out of *variable* immediately, before execution of any other function call.

This is much like **gcc**'s local functions, except that the GNU C local functions have dynamic extent (i.e. are deallocated when the creating function returns), while *trampoline* provides functions with indefinite extent: *function* is only deallocated when **free\_trampoline(***function***)** is called.

**is\_trampoline(***function***)** checks whether the C function *function* was produced by a call to *alloc\_trampoline*. If this returns true, the arguments given to *alloc\_trampoline* can be retrieved:

**trampoline\_address(***function***)** returns *address*,

**trampoline\_variable(***function***)** returns *variable*,

**trampoline\_data(***function***)** returns *data*.

## SEE ALSO

[**gcc**(1)](/gcc/1.md), [**stdarg**(3)](/stdarg/3.md), [**callback**(3)](/callback/3.md)

## BUGS

Passing the data through a global variable is not reentrant. Don't call trampoline functions from within signal handlers. This is fixed in the [**callback**(3)](/callback/3.md) package.

## PORTING

The way **gcc** builds local functions is described in the gcc source, file gcc-2.6.3/config/*cpu*/*cpu*.h.

## AUTHOR

Bruno Haible \<bruno@clisp.org\>

## ACKNOWLEDGEMENTS

Many ideas were cribbed from the gcc source.