---
title: Blazing Fast Data Processing with V8
sidebar_label: C++ + V8
description: Process structured data in C++ or Rust programs. Seamlessly integrate spreadsheets by paring V8 and SheetJS. Modernize  workflows while preserving Excel compatibility.
pagination_prev: demos/bigdata/index
pagination_next: solutions/input
---

import current from '/version.js';
import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';
import CodeBlock from '@theme/CodeBlock';

[V8](https://v8.dev/) is an embeddable JavaScript engine written in C++. It
powers Chromium and Chrome, NodeJS and Deno, Adobe UXP and other platforms.

[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.

This demo uses V8 and SheetJS to read and write spreadsheets. We'll explore how
to load SheetJS in a V8 context and process spreadsheets and structured data from
C++ and Rust programs.

The ["Complete Example"](#complete-example) creates a C++ command-line tool for
reading spreadsheet files and generating new workbooks. ["Bindings"](#bindings)
covers V8 engine bindings for other programming languages.

## Integration Details

The [SheetJS Standalone scripts](/docs/getting-started/installation/standalone)
can be parsed and evaluated in a V8 context.

_Initialize V8_

The official V8 `hello-world` example covers initialization and cleanup. For the
purposes of this demo, the key variables are noted below:

```cpp
v8::Isolate* isolate = v8::Isolate::New(create_params);
v8::Local<v8::Context> context = v8::Context::New(isolate);
```

The following helper function evaluates C strings as JS code:

```cpp
v8::Local<v8::Value> eval_code(v8::Isolate *isolate, v8::Local<v8::Context> context, char* code, size_t sz = -1) {
  v8::Local<v8::String> source = v8::String::NewFromUtf8(isolate, code, v8::NewStringType::kNormal, sz).ToLocalChecked();
  v8::Local<v8::Script> script = v8::Script::Compile(context, source).ToLocalChecked();
  return script->Run(context).ToLocalChecked();
}
```

_Load SheetJS Scripts_

The main library can be loaded by reading the scripts from the file system and
evaluating in the V8 context:

```cpp
/* simple wrapper to read the entire script file */
static char *read_file(const char *filename, size_t *sz) {
  FILE *f = fopen(filename, "rb");
  if(!f) return NULL;
  long fsize; { fseek(f, 0, SEEK_END); fsize = ftell(f); fseek(f, 0, SEEK_SET); }
  char *buf = (char *)malloc(fsize * sizeof(char));
  *sz = fread((void *) buf, 1, fsize, f);
  fclose(f);
  return buf;
}

// ...
  size_t sz; char *file = read_file("xlsx.full.min.js", &sz);
  v8::Local<v8::Value> result = eval_code(isolate, context, file, sz);
```

To confirm the library is loaded, `XLSX.version` can be inspected:

```cpp
  /* get version string */
  v8::Local<v8::Value> result = eval_code(isolate, context, "XLSX.version");
  v8::String::Utf8Value vers(isolate, result);
  printf("SheetJS library version %s\n", *vers);
```

### Reading Files

V8 supports `ArrayBuffer` natively. Assuming `buf` is a C byte array, with
length `len`, this snippet stores the data as an `ArrayBuffer` in global scope:

```cpp
/* load C char array and save to an ArrayBuffer */
std::unique_ptr<v8::BackingStore> back = v8::ArrayBuffer::NewBackingStore(isolate, len);
memcpy(back->Data(), buf, len);
v8::Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, std::move(back));
v8::Maybe<bool> res = context->Global()->Set(context, v8::String::NewFromUtf8Literal(isolate, "buf"), ab);

/* parse with SheetJS */
v8::Local<v8::Value> result = eval_code(isolate, context, "globalThis.wb = XLSX.read(buf)");
```

`wb` will be a variable in the JS environment that can be inspected using the
various SheetJS API functions.

### Writing Files

The underlying memory from an `ArrayBuffer` can be recovered:

```c
/* write with SheetJS using type: "array" */
v8::Local<v8::Value> result = eval_code(isolate, context, "XLSX.write(wb, {type:'array', bookType:'xlsb'})");

/* pull result back to C++ */
v8::Local<v8::ArrayBuffer> ab = v8::Local<v8::ArrayBuffer>::Cast(result);
size_t sz = ab->ByteLength();
char *buf = ab->Data();
```

The resulting `buf` can be written to file with `fwrite`.

## Complete Example

:::note

This demo was tested in the following deployments:

| V8 Version    | Platform     | OS Version   | Compiler         | Date       |
|:--------------|:-------------|:-------------|:-----------------|:-----------|
| `11.8.82`     | `darwin-x64` | macOS 13.5.1 | `clang 14.0.3`   | 2023-08-26 |
| `11.8.82`     | `darwin-arm` | macOS 13.5.1 | `clang 14.0.3`   | 2023-08-26 |
| `11.8.82`     | `win10-x64`  | Windows 10   | `CL 19.37.32822` | 2023-08-26 |
| `11.3.244.11` | `linux-x64`  | HoloOS 3.4.6 | `gcc 12.2.0`     | 2023-05-20 |

:::

This program parses a file and prints CSV data from the first worksheet. It also
generates an XLSB file and writes to the filesystem.

:::caution pass

When the demo was last tested, there were errors in the official V8 embed guide.
The correct instructions are included below.

:::

:::caution pass

The build process is long and will test your patience.

:::

### Preparation

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

0) Prepare `/usr/local/lib`:

```bash
mkdir -p /usr/local/lib
cd /usr/local/lib
```

:::caution pass

If this step throws a permission error, run:

```bash
sudo mkdir -p /usr/local/lib
sudo chmod 777 /usr/local/lib
```

:::

  </TabItem>
  <TabItem value="win" label="Windows">

0) Follow the official ["Visual Studio"](https://chromium.googlesource.com/chromium/src/+/master/docs/windows_build_instructions.md#visual-studio)
installation steps.

:::info pass

Using the installer tool, the "Desktop development with C++" workload must be
installed. In the sidebar, verify the following components are checked:

- "C++ ATL for latest ... build tools" (`v143` when last tested)
- "C++ MFC for latest ... build tools" (`v143` when last tested)

In the "Individual components" tab, search for "Windows 11 SDK" and verify that
"Windows 11 SDK (10.0.22621.0)" is checked.

Click "Modify" and allow the installer to finish.

The SDK debugging tools must be installed after the SDK is installed.

1) Using the Search bar, search "Apps & features".

2) When the setting panel opens, scroll down to "Windows Software Development
Kit - Windows 10.0.22621 and click "Modify".

3) In the new window, select "Change" and click "Next"

4) Check "Debugging Tools for Windows" and click "Change"

:::

The following `git` settings should be changed:

```bash
git config --global core.autocrlf false
git config --global core.filemode false
git config --global branch.autosetuprebase always
```

  </TabItem>
</Tabs>


1) Download and install `depot_tools`:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
```

  </TabItem>
  <TabItem value="win" label="Windows">

[The bundle](https://storage.googleapis.com/chrome-infra/depot_tools.zip) is a
ZIP file that should be downloaded and extracted.

The demo was last tested on an exFAT-formatted drive (mounted at `E:\`).

After extracting, verify that the `depot_tools` folder is not read-only.

  </TabItem>
</Tabs>

2) Add the path to the `PATH` environment variable:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
export PATH="/usr/local/lib/depot_tools:$PATH"
```

At this point, it is strongly recommended to add the line to a shell startup
script such as `.bashrc` or `.zshrc`

  </TabItem>
  <TabItem value="win" label="Windows">

:::caution pass

These instructions are for `cmd` use. Do not run in PowerShell!

It is strongly recommended to use the "Developer Command Prompt" from Visual
Studio as it prepares the console to run build tools.

:::

```bash
set DEPOT_TOOLS_WIN_TOOLCHAIN=0
set PATH=E:\depot_tools;%PATH%
```

In addition, the `vs2022_install` variable must be set to the Visual Studio
folder. For example, using the "Community Edition", the assignment should be

```bash
set vs2022_install="C:\Program Files\Microsoft Visual Studio\2022\Community"
```

These environment variables can be persisted in the Control Panel.

  </TabItem>
</Tabs>

3) Run `gclient` once to update `depot_tools`:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
gclient
```

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
gclient
```

:::caution pass

`gclient` may throw errors related to `git` and permissions issues:

```
fatal: detected dubious ownership in repository at 'E:/depot_tools'
'E:/depot_tools' is on a file system that doesnot record ownership
To add an exception for this directory, call:

        git config --global --add safe.directory E:/depot_tools
```

These issues are related to the exFAT file system. They were resolved by running
the recommended commands and re-running `gclient`.

:::

:::caution pass

There were errors pertaining to `gitconfig`:

```
error: could not write config file E:/depot_tools/bootstrap-2@3_8_10_chromium_26_bin/git/etc/gitconfig: File exists
```

This can happen if the `depot_tools` folder is read-only. The workaround is to
unset the read-only flag for the `E:\depot_tools` folder.

:::

  </TabItem>
</Tabs>

### Clone V8

4) Create a base directory:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
mkdir -p ~/dev/v8
cd ~/dev/v8
fetch v8
cd v8
```

Note that the actual repo will be placed in `~/dev/v8/v8`.

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
cd E:\
mkdir v8
cd v8
fetch v8
cd v8
```

:::caution pass

On exFAT, every cloned repo elicited the same `git` permissions error. `fetch`
will fail with a clear remedy message such as

```
        git config --global --add safe.directory E:/v8/v8
```

Run the command then run `gclient sync`, repeating each time the command fails.

:::

:::caution pass

There were occasional `git` conflict errors:

```
v8/tools/clang (ERROR)
----------------------------------------
[0:00:01] Started.
...
error: Your local changes to the following files would be overwritten by checkout:
        plugins/FindBadRawPtrPatterns.cpp
...
Please commit your changes or stash them before you switch branches.
Aborting
error: could not detach HEAD
----------------------------------------
Error: 28> Unrecognized error, please merge or rebase manually.
28> cd E:\v8\v8\tools\clang && git rebase --onto 65ceb79efbc9d1dec9b1a0f4bc0b8d010b9d7a66 refs/remotes/origin/main
```

The recommended fix is to delete the referenced folder and re-run `gclient sync`

:::

  </TabItem>
</Tabs>


5) Checkout the desired version. The following command pulls `11.8.82`:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
git checkout refs/tags/11.8.82 -b sample -t
```

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
git checkout tags/11.8.82 -b sample
```

:::caution pass

The official documentation recommends:

```bash
git checkout refs/tags/11.8.82 -b sample -t
```

This command failed in local testing:

```
E:\v8\v8>git checkout refs/tags/11.8.82 -b sample -t
fatal: cannot set up tracking information; starting point 'refs/tags/11.8.82' is not a branch
```

:::

  </TabItem>
</Tabs>

### Build V8

6) Build the static library.

<Tabs groupId="triple">
  <TabItem value="darwin-x64" label="Intel Mac">

```bash
tools/dev/v8gen.py x64.release.sample
ninja -C out.gn/x64.release.sample v8_monolith
```

  </TabItem>
  <TabItem value="darwin-arm" label="Apple Silicon">

```bash
tools/dev/v8gen.py arm64.release.sample
ninja -C out.gn/arm64.release.sample v8_monolith
```

  </TabItem>
  <TabItem value="win10-x64" label="Windows">

```bash
python3 tools\dev\v8gen.py -vv x64.release.sample
ninja -C out.gn\x64.release.sample v8_monolith
```

:::caution pass

In local testing, the build sometimes failed with a `dbghelp.dll` error:

```
 Exception: dbghelp.dll not found in "C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\dbghelp.dll"
```

This issue was fixed by removing and reinstalling "Debugging Tools for Windows"
from the Control Panel as described in step 0.

:::

:::caution pass

In local testing, the `ninja` build failed with C++ deprecation errors:

```c++
../..\src/wasm/wasm-code-manager.h(789,28): error: 'atomic_load<v8::base::OwnedVector<const unsigned char>>' is deprecated: warning STL4029: std::atomic_*() overloads for shared_ptr are deprecated in C++20. The shared_ptr specialization of std::atomic provides superior functionality. You can define _SILENCE_CXX20_OLD_SHARED_PTR_ATOMIC_SUPPORT_DEPRECATION_WARNING or _SILENCE_ALL_CXX20_DEPRECATION_WARNINGS to suppress this warning. [-Werror,-Wdeprecated-declarations]
  789 |     auto wire_bytes = std::atomic_load(&wire_bytes_);
      |                            ^
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.37.32822\include\memory(3794,1): note: 'atomic_load<v8::base::OwnedVector<const unsigned char>>' has been explicitly marked deprecated here
 3794 | _CXX20_DEPRECATE_OLD_SHARED_PTR_ATOMIC_SUPPORT _NODISCARD shared_ptr<_Ty> atomic_load(
      | ^
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.37.32822\include\yvals_core.h(1317,7): note: expanded from macro '_CXX20_DEPRECATE_OLD_SHARED_PTR_ATOMIC_SUPPORT'
 1317 |     [[deprecated("warning STL4029: "                                                                \
      |       ^
2 errors generated.
[14/1303] CXX obj/torque_generated_definitions/js-atomics-synchronization-tq.obj
FAILED: obj/torque_generated_definitions/js-atomics-synchronization-tq.obj
```

The workaround is to append a line to `out.gn\x64.release.sample\args.gn`:

```text title="out.gn\x64.release.sample\args.gn (add to end)"
treat_warnings_as_errors = false
```

:::

  </TabItem>
</Tabs>

7) Ensure the sample `hello-world` compiles and runs:

<Tabs groupId="triple">
  <TabItem value="darwin-x64" label="Intel Mac">

```bash
g++ -I. -Iinclude samples/hello-world.cc -o hello_world -fno-rtti -lv8_monolith \
    -lv8_libbase -lv8_libplatform -ldl -Lout.gn/x64.release.sample/obj/ -pthread \
    -std=c++17 -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
./hello_world
```

  </TabItem>
  <TabItem value="darwin-arm" label="Apple Silicon">

```bash
g++ -I. -Iinclude samples/hello-world.cc -o hello_world -fno-rtti -lv8_monolith \
    -lv8_libbase -lv8_libplatform -ldl -Lout.gn/arm64.release.sample/obj/ -pthread \
    -std=c++17 -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
./hello_world
```

  </TabItem>
  <TabItem value="win10-x64" label="Windows">

```bash
cl /I. /Iinclude samples/hello-world.cc /GR- v8_monolith.lib Advapi32.lib Winmm.lib Dbghelp.lib /std:c++17 /DV8_COMPRESS_POINTERS=1 /DV8_ENABLE_SANDBOX /link /out:hello_world.exe /LIBPATH:out.gn\x64.release.sample\obj\
.\hello_world.exe
```

  </TabItem>
</Tabs>


### Prepare Project

8) Make a new project folder:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
cd ~/dev
mkdir -p sheetjs-v8
cd sheetjs-v8
```

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
cd E:\
mkdir sheetjs-v8
cd sheetjs-v8
```

  </TabItem>
</Tabs>

9) Copy the sample source:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
cp ~/dev/v8/v8/samples/hello-world.cc .
```

10) Create symbolic links to the `include` headers and `obj` library folders:

<Tabs groupId="triple">
  <TabItem value="darwin-x64" label="Intel Mac">

```bash
ln -s ~/dev/v8/v8/include
ln -s ~/dev/v8/v8/out.gn/x64.release.sample/obj
```

  </TabItem>
  <TabItem value="darwin-arm" label="Apple Silicon">

```bash
ln -s ~/dev/v8/v8/include
ln -s ~/dev/v8/v8/out.gn/arm64.release.sample/obj
```

  </TabItem>
</Tabs>

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
copy E:\v8\v8\samples\hello-world.cc .\
```

10) Observe that exFAT does not support symbolic links and move on to step 11.

  </TabItem>
</Tabs>

11) Build and run the `hello-world` example from this folder:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
g++ -I. -Iinclude hello-world.cc -o hello_world -fno-rtti -lv8_monolith \
    -lv8_libbase -lv8_libplatform -ldl -Lobj/ -pthread -std=c++17 \
    -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
./hello_world
```

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
cl /MT /I..\v8\v8\ /I..\v8\v8\include hello-world.cc /GR- v8_monolith.lib Advapi32.lib Winmm.lib Dbghelp.lib /std:c++17 /DV8_COMPRESS_POINTERS=1 /DV8_ENABLE_SANDBOX /link /out:hello_world.exe /LIBPATH:..\v8\v8\out.gn\x64.release.sample\obj\
.\hello_world.exe
```

  </TabItem>
</Tabs>

### Add SheetJS

12) Download the standalone script and test file:

<ul>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}>xlsx.full.min.js</a></li>
<li><a href="https://sheetjs.com/pres.numbers">pres.numbers</a></li>
</ul>

<CodeBlock language="bash">{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
curl -LO https://sheetjs.com/pres.numbers`}
</CodeBlock>

13) Download [`sheetjs.v8.cc`](pathname:///v8/sheetjs.v8.cc):

```bash
curl -LO https://docs.sheetjs.com/v8/sheetjs.v8.cc
```

14) Compile standalone `sheetjs.v8` binary

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
g++ -I. -Iinclude sheetjs.v8.cc -o sheetjs.v8 -fno-rtti -lv8_monolith \
    -lv8_libbase -lv8_libplatform -ldl -Lobj/ -pthread -std=c++17 \
    -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
```

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
cl /MT /I..\v8\v8\ /I..\v8\v8\include sheetjs.v8.cc /GR- v8_monolith.lib Advapi32.lib Winmm.lib Dbghelp.lib /std:c++17 /DV8_COMPRESS_POINTERS=1 /DV8_ENABLE_SANDBOX /link /out:sheetjs.v8.exe /LIBPATH:..\v8\v8\out.gn\x64.release.sample\obj\
```

  </TabItem>
</Tabs>

15) Run the demo:

<Tabs groupId="os">
  <TabItem value="unix" label="Linux/MacOS">

```bash
./sheetjs.v8 pres.numbers
```

  </TabItem>
  <TabItem value="win" label="Windows">

```bash
cl /MT /I..\v8\v8\ /I..\v8\v8\include sheetjs.v8.cc /GR- v8_monolith.lib Advapi32.lib Winmm.lib Dbghelp.lib /std:c++17 /DV8_COMPRESS_POINTERS=1 /DV8_ENABLE_SANDBOX /link /out:sheetjs.v8.exe /LIBPATH:..\v8\v8\out.gn\x64.release.sample\obj\
```

  </TabItem>
</Tabs>

If the program succeeded, the CSV contents will be printed to console and the
file `sheetjsw.xlsb` will be created.  That file can be opened with Excel.

## Bindings

Bindings exist for many languages. As these bindings require "native" code, they
may not work on every platform.

### Rust

The `v8` crate provides binary builds and straightforward bindings. The Rust
code is similar to the C++ code.

Pulling data from an `ArrayBuffer` back into Rust involves an unsafe operation:

```rust
/* assuming JS code returns an ArrayBuffer, copy result to a Vec<u8> */
fn eval_code_ab(scope: &mut v8::HandleScope, code: &str) -> Vec<u8> {
  let source = v8::String::new(scope, &code).unwrap();
  let script = v8::Script::compile(scope, source, None).unwrap();
  let result: v8::Local<v8::ArrayBuffer> = script.run(scope).unwrap().try_into().unwrap();
  /* In C++, `Data` returns a pointer. Collecting data into Vec<u8> is unsafe */
  unsafe { return std::slice::from_raw_parts_mut(
    result.data().unwrap().cast::<u8>().as_ptr(),
    result.byte_length()
  ).to_vec(); }
}
```

:::note

This demo was last tested in the following deployments:

| Architecture | V8 Crate | Date       |
|:-------------|:---------|:-----------|
| `darwin-x64` | `0.75.1` | 2023-08-26 |
| `darwin-arm` | `0.73.0` | 2023-06-05 |
| `linux-x64`  | `0.71.2` | 2023-05-23 |
| `win10-x64`  | `0.71.2` | 2023-05-23 |

:::

1) Create a new project:

```bash
cargo new sheetjs-rustyv8
cd sheetjs-rustyv8
cargo run
```

2) Add the `v8` crate:

```bash
cargo add v8
cargo run
```

3) Download the [Standalone build](/docs/getting-started/installation/standalone):

<CodeBlock language="bash">{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}
</CodeBlock>

4) Download [`main.rs`](pathname:///v8/main.rs) and replace `src/main.rs`:

```bash
curl -L -o src/main.rs https://docs.sheetjs.com/v8/main.rs
```

5) Download [the test file](https://sheetjs.com/pres.numbers) and run:

```bash
curl -LO https://sheetjs.com/pres.numbers
cargo run pres.numbers
```

If the program succeeded, the CSV contents will be printed to console and the
file `sheetjsw.xlsb` will be created.  That file can be opened with Excel.