---
title: "longjmp and setjmp in WASIX"
description: "This sample project demonstrates how longjmp and setjmp works in WASIX."
url: "https://wasix.org/docs/language-guide/c/tutorials/longjmp/"
markdown: "https://wasix.org/docs/language-guide/c/tutorials/longjmp.md"
---

# `longjmp` and `setjmp` in WASIX

This sample project demonstrates how longjmp and setjmp works in WASIX.

## Prerequisites

> ⚠️
>
> Please check that you have the latest version of wasmer runtime as this tutorial depends on version **4.1.1** or higher.

The project requires the following tools to be installed on your system:

- [wasi-sdk ](https://github.com/WebAssembly/wasi-sdk)
- [wasix-libc ](https://github.com/wasix-org/wasix-libc)

## Start a new project

### Create a new directory for your project:

```shell
$ mkdir wasix-jump
$ cd wasix-jump
```

### Make a new file called jump.c:

```shell
$ touch jump.c
```

### Link the SysRoot

> ℹ️
>
> You need to link the SysRoot to your project. The SysRoot is a directory that contains the WASI libc headers and libraries. The SysRoot is located in the Wasix-libc binary or you can compile it yourself.

## Writing the Application

### Basic Application Setup

We want to write a simple C program that demonstrates how to use the `opendir` and `jump` functions to read the contents of a directory. It takes a single command-line argument, which is the path to the directory to read.

Let’s write code for the above:

File: `jump.c`

```c
#include <stdio.h>
#include <setjmp.h>

jmp_buf bufferA, bufferB;

__attribute__((noinline)) void routineB(); // forward declaration

__attribute__((noinline)) void routineA()
{
    int r = 1;

    printf("(A1)\n");

    r = setjmp(bufferA); // save the current context in bufferA
    if (r == 0)
        routineB(); // call routineB() and pass control to it

    printf("(A2) r=%d\n", r); // r will be 10001

    r = setjmp(bufferA);
    if (r == 0)
        longjmp(bufferB, 20001); // pass control to bufferB and return 20001

    printf("(A3) r=%d\n", r); // r will be 10002

    r = setjmp(bufferA);
    if (r == 0)
        longjmp(bufferB, 20002); // pass control to bufferB and return 20002

    printf("(A4) r=%d\n", r); // r will be 10003
}

__attribute__((noinline)) void routineB()
{
    int r;

    printf("(B1)\n");

    r = setjmp(bufferB); // save the current context in bufferB
    if (r == 0)
        longjmp(bufferA, 10001); // pass control to bufferA and return 10001

    printf("(B2) r=%d\n", r); // r will be 20001

    r = setjmp(bufferB);
    if (r == 0)
        longjmp(bufferA, 10002); // pass control to bufferA and return 10002

    printf("(B3) r=%d\n", r); // r will be 20002

    r = setjmp(bufferB);
    if (r == 0)
        longjmp(bufferA, 10003); // pass control to bufferA and return 10003
}

int main(int argc, char **argv)
{
    routineA(); // call routineA() and pass control to it
    return 0;
}
```

### Compiling the Application

Let’s compile the application with WASIX:

```shell
$ /path/to/wasix-sdk/clang jump.c --target="wasm32-wasi" -o jump.wasm
```

It’s compiling! Now, let’s try to run it:

```shell
$ wasmer run jump.wasm /
(A1)
(B1)
(A2) r=10001
(B2) r=20001
(A3) r=10002
(B3) r=20002
(A4) r=10003
```

Yaay, It works!

# Conclusion

In this tutorial we learned:

- How to use `longjmp` and `setjmp` in C
- Compiling a C program with WASIX

[wasix-libc/examples/longjmp.c](https://github.com/wasix-org/wasix-libc/tree/main/examples/longjmp.c)

---

[Documentation index](https://wasix.org/llms.txt) · [HTML version](https://wasix.org/docs/language-guide/c/tutorials/longjmp/)