writeFile

Write data to a new file in the CheerpX DataDevice.

namespace CheerpX {
  class DataDevice {
    async writeFile(
      filename: string,
      contents: string | Uint8Array
    ): Promise<void>;
  }
}

Parameters

filename (string) - The path to the file within the device, starting with a / (e.g., /filename). The path should not include the mount point.
contents (string | Uint8Array) - The data to write to the file. Can be either a string or a Uint8Array.

Returns

CheerpX.DataDevice.writeFile returns a Promise that resolves when the file has been created and written to, but it does not return any value.

Example

Write a file to the DataDevice.

// Create a read-only block device for a disk image stored on the HTTP server
const blockDevice = await CheerpX.HttpBytesDevice.create("/cheerpXImage.ext2");
// Make the block device read-write using a persistent IndexedDB overlay
const idbDevice = await CheerpX.IDBDevice.create("block_cpp");
const overlayDevice = await CheerpX.OverlayDevice.create(
  blockDevice,
  idbDevice
);
// Add a device to expose JavaScript data in the VM
const dataDevice = await CheerpX.DataDevice.create();
// Initialize the CheerpX environment
const mountPoints = [
  // Use the disk image as the filesystem root
  { type: "ext2", path: "/", dev: overlayDevice },
  // Add the DataDevice to a known location
  { type: "dir", path: "/data", dev: dataDevice },
  // Add the required Linux pseudo-filesystem
  { type: "devs", path: "/dev" },
  { type: "devpts", path: "/dev/pts" },
  { type: "proc", path: "/proc" },
];
const cx = await CheerpX.Linux.create({
  mounts: mountPoints,
});

// Setup the text console
cx.setConsole(document.getElementById("console"));

async function compileAndRun(cx, dataDevice, srcCode, inputName, outputName) {
  // Make the source code available as a file
  await dataDevice.writeFile("/" + inputName, srcCode);
  // Compile the source code by calling g++
  await cx.run(
    "/usr/bin/g++",
    ["-v", "/data/" + inputName, "-o", "/" + outputName],
    {
      env: ["PATH=/usr/bin"],
    }
  );
  await cx.run("/" + outputName, []);
}

const srcCode = `
#include <iostream>

int main()
{
    std::cout << "Hello World" << std::endl;
    return 0;
}
`;
await compileAndRun(cx, dataDevice, srcCode, "hello.cpp", "hello");

In this example:

The writeFile method is used to write source code (srcCode) into a file (hello.cpp) on the DataDevice.

After that, the CheerpX environment runs a g++ command to compile the source code, and then executes the compiled file to output Hello World.

If you’d like to learn more about related topics, check out these guides:

Files and filesystems – Managing files and storage in CheerpX.
Custom disk images – Creating and using custom disk images.
Input and output – Handling data flow in your environment.