---
title: Data Processing with Duktape
sidebar_label: C + Duktape
description: Process structured data in C programs. Seamlessly integrate spreadsheets into your program by pairing Duktape and SheetJS. Supercharge programs with modern data tools.
pagination_prev: demos/bigdata/index
pagination_next: solutions/input
---
import current from '/version.js';
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[Duktape](https://duktape.org) is an embeddable JS engine written in C. It has
been ported to a number of exotic architectures and operating systems.
[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.
The ["Complete Example"](#complete-example) section includes a complete
command-line tool for reading data from spreadsheets and exporting to Excel XLSB
workbooks.
The ["Bindings"](#bindings) section covers bindings for other ecosystems.
## Integration Details
### Initialize Duktape
Duktape does not provide a `global` variable. It can be created in one line:
```c
/* initialize */
duk_context *ctx = duk_create_heap_default();
/* duktape does not expose a standard "global" by default */
// highlight-next-line
duk_eval_string_noresult(ctx, "var global = (function(){ return this; }).call(null);");
```
### Load SheetJS Scripts
The [SheetJS Standalone scripts](/docs/getting-started/installation/standalone)
can be parsed and evaluated in a Duktape context.
The shim and main libraries can be loaded by reading the scripts from the file
system and evaluating in the Duktape context:
```c
/* simple wrapper to read the entire script file */
static duk_int_t eval_file(duk_context *ctx, const char *filename) {
size_t len;
/* read script from filesystem */
FILE *f = fopen(filename, "rb");
if(!f) { duk_push_undefined(ctx); perror("fopen"); return 1; }
long fsize; { fseek(f, 0, SEEK_END); fsize = ftell(f); fseek(f, 0, SEEK_SET); }
char *buf = (char *)malloc(fsize * sizeof(char));
len = fread((void *) buf, 1, fsize, f);
fclose(f);
if(!buf) { duk_push_undefined(ctx); perror("fread"); return 1; }
// highlight-start
/* load script into the context */
duk_push_lstring(ctx, (const char *)buf, (duk_size_t)len);
/* eval script */
duk_int_t retval = duk_peval(ctx);
/* cleanup */
duk_pop(ctx);
// highlight-end
return retval;
}
// ...
duk_int_t res = 0;
if((res = eval_file(ctx, "shim.min.js")) != 0) { /* error handler */ }
if((res = eval_file(ctx, "xlsx.full.min.js")) != 0) { /* error handler */ }
```
To confirm the library is loaded, `XLSX.version` can be inspected:
```c
/* get version string */
duk_eval_string(ctx, "XLSX.version");
printf("SheetJS library version %s\n", duk_get_string(ctx, -1));
duk_pop(ctx);
```
### Reading Files
Duktape supports `Buffer` natively but should be sliced before processing.
Assuming `buf` is a C byte array, with length `len`, this snippet parses data:
```c
/* load C char array and save to a Buffer */
duk_push_external_buffer(ctx);
duk_config_buffer(ctx, -1, buf, len);
duk_put_global_string(ctx, "buf");
/* parse with SheetJS */
duk_eval_string_noresult(ctx, "workbook = XLSX.read(buf.slice(0, buf.length), {type:'buffer'});");
```
`workbook` will be a variable in the JS environment that can be inspected using
the various SheetJS API functions.
### Writing Files
`duk_get_buffer_data` can pull `Buffer` object data into the C code:
```c
/* write with SheetJS using type: "array" */
duk_eval_string(ctx, "XLSX.write(workbook, {type:'array', bookType:'xlsx'})");
/* pull result back to C */
duk_size_t sz;
char *buf = (char *)duk_get_buffer_data(ctx, -1, sz);
/* discard result in duktape */
duk_pop(ctx);
```
The resulting `buf` can be written to file with `fwrite`.
## Complete Example
:::note Tested Deployments
This demo was tested in the following deployments:
| Architecture | Version | Date |
|:-------------|:--------|:-----------|
| `darwin-x64` | `2.7.0` | 2024-04-04 |
| `darwin-arm` | `2.7.0` | 2023-10-18 |
| `win10-x64` | `2.7.0` | 2024-03-27 |
| `win11-arm` | `2.7.0` | 2023-12-01 |
| `linux-x64` | `2.7.0` | 2024-03-21 |
| `linux-arm` | `2.7.0` | 2023-12-01 |
:::
This program parses a file and prints CSV data from the first worksheet. It also
generates an XLSB file and writes to the filesystem.
The [flow diagram is displayed after the example steps](#flow-diagram)
:::info pass
On Windows, the Visual Studio "Native Tools Command Prompt" must be used.
:::
0) Create a project folder:
```bash
mkdir sheetjs-duk
cd sheetjs-duk
```
1) Download and extract Duktape:
:::caution pass
The Windows built-in `tar` does not support `xz` archives.
**The commands must be run within WSL `bash`.**
After the `mv` command, exit WSL.
:::
```bash
curl -LO https://duktape.org/duktape-2.7.0.tar.xz
tar -xJf duktape-2.7.0.tar.xz
mv duktape-2.7.0/src/*.{c,h} .
```
2) Download the SheetJS Standalone script, shim script and test file. Move all
three files to the project directory:
:::caution pass
If the `curl` command fails, run the commands within WSL `bash`.
:::
{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
curl -LO https://sheetjs.com/pres.numbers`}
3) Download [`sheetjs.duk.c`](pathname:///duk/sheetjs.duk.c):
```bash
curl -LO https://docs.sheetjs.com/duk/sheetjs.duk.c
```
4) Compile standalone `sheetjs.duk` binary
```bash
gcc -std=c99 -Wall -osheetjs.duk sheetjs.duk.c duktape.c -lm
```
:::note pass
GCC may generate a warning:
```
duk_js_compiler.c:5628:13: warning: variable 'num_stmts' set but not used [-Wunused-but-set-variable]
duk_int_t num_stmts;
^
```
This warning can be ignored.
:::
```powershell
cl sheetjs.duk.c duktape.c /I .\
```
5) Run the demo:
```bash
./sheetjs.duk pres.numbers
```
```bash
.\sheetjs.duk.exe 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.
### Flow Diagram
```mermaid
sequenceDiagram
participant F as Filesystem
participant C as C Code
participant D as Duktape
activate C
opt
Note over F,D: ~ Prepare Duktape ~
C->>+D: Initialize
deactivate C
D->>-C: Done
activate C
C->>F: Need SheetJS
F->>C: SheetJS Code
C->>+D: Load SheetJS Code
deactivate C
D->>-C: Loaded
activate C
C->>+D: Execute Code
deactivate C
Note over D: Eval SheetJS Code
D->>-C: Done
activate C
Note over D: XLSX
ready to rock
end
opt
Note over F,D: ~ Parse File ~
C->>F: Read Spreadsheet
F->>C: Spreadsheet File
C->>+D: Load Data
deactivate C
D->>-C: Loaded
activate C
C->>+D: eval `var workbook = XLSX.read(...)`
deactivate C
Note over D: Parse File
D->>-C: Done
activate C
Note over D: `workbook`
can be used later
end
opt
Note over F,D: ~ Print CSV to screen ~
C->>+D: eval `XLSX.utils.sheet_to_csv(...)`
deactivate C
Note over D: Generate CSV
D->>-C: CSV Data
activate C
Note over C: Print to standard output
end
opt
Note over F,D: ~ Write XLSB File ~
C->>+D: eval `XLSX.write(...)`
deactivate C
Note over D: Generate File
D->>-C: done
activate C
C->>+D: get file bytes
deactivate C
D->>-C: binary data
activate C
C->>F: Write File
end
deactivate C
```
## Bindings
Bindings exist for many languages. As these bindings require "native" code, they
may not work on every platform.
The Duktape source distribution includes a separate Makefile for building a
shared library. This library can be loaded in other programs.
#### Blingos
Duktape includes a number of "blingos" (function-like macros) which will not be
included in the shared library. The macros must be manually expanded.
For example, `duk_create_heap_default` is defined as follows:
```c
#define duk_create_heap_default() \
duk_create_heap(NULL, NULL, NULL, NULL, NULL)
```
The `duk_create_heap_default` blingo will not be defined in the shared library.
Instead, `duk_create_heap` must be called directly. Using PHP FFI:
```php
/* create new FFI object */
$ffi = FFI::cdef(/* ... arguments */);
/* call duk_create_heap directly */
// highlight-next-line
$context = $ffi->duk_create_heap(null, null, null, null, null);
```
#### Null Pointers
The C `NULL` pointer must be used in some functions. Some FFI implementations
have special values distinct from the language-native null value. Using Python,
return type hints are specified with the `restype` property:
```py
from ctypes import CDLL, c_void_p
duk = CDLL("libduktape.so")
# highlight-next-line
duk.duk_create_heap.restype = c_void_p
context = duk.duk_create_heap(None, None, None, None, None)
```
### PHP
There is no official PHP binding to the Duktape library. Instead, this demo uses
the raw `FFI` interface[^1] to the Duktape shared library.
The [`SheetJSDuk.php`](pathname:///duk/SheetJSDuk.php) demo script parses a
file, prints CSV rows from the first worksheet, and creates a XLSB workbook.
#### PHP Demo
:::note Tested Deployments
This demo was tested in the following deployments:
| Architecture | Version | PHP Version | Date |
|:-------------|:--------|:------------|:-----------|
| `darwin-x64` | `2.7.0` | `8.3.4` | 2024-03-15 |
| `darwin-arm` | `2.7.0` | `8.3.2` | 2024-02-13 |
| `linux-x64` | `2.7.0` | `8.2.7` | 2024-03-21 |
:::
0) Ensure `php` is installed and available on the system path
1) Find the `php.ini` file:
```bash
php --ini
```
The following output is from the last macOS test:
```text pass
Configuration File (php.ini) Path: /usr/local/etc/php/8.3
// highlight-next-line
Loaded Configuration File: /usr/local/etc/php/8.3/php.ini
Scan for additional .ini files in: /usr/local/etc/php/8.3/conf.d
Additional .ini files parsed: /usr/local/etc/php/8.3/conf.d/ext-opcache.ini
```
2) Edit the `php.ini` configuration file.
The following line should appear in the configuration:
```ini title="php.ini (add to end)"
extension=ffi
```
If this line is prefixed with a `;`, remove the semicolon. If this line does not
appear in the file, add it to the end.
3) Build the Duktape shared library:
```bash
curl -LO https://duktape.org/duktape-2.7.0.tar.xz
tar -xJf duktape-2.7.0.tar.xz
cd duktape-2.7.0
make -f Makefile.sharedlibrary
cd ..
```
4) Copy the shared library to the current folder. When the demo was last tested,
the shared library file name differed by platform:
| OS | name |
|:-------|:--------------------------|
| Darwin | `libduktape.207.20700.so` |
| Linux | `libduktape.so.207.20700` |
```bash
cp duktape-*/libduktape.* .
```
5) Download the SheetJS Standalone script, shim script and test file. Move all
three files to the project directory:
{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
curl -LO https://sheetjs.com/pres.numbers`}
6) Download [`SheetJSDuk.php`](pathname:///duk/SheetJSDuk.php):
```bash
curl -LO https://docs.sheetjs.com/duk/SheetJSDuk.php
```
7) Edit the `SheetJSDuk.php` script.
The `$sofile` variable declares the path to the library:
```php title="SheetJSDuk.php (edit highlighted line)"
The name of the library is `libduktape.207.20700.so`:
```php title="SheetJSDuk.php (change highlighted line)"
// highlight-next-line
$sofile = './libduktape.207.20700.so';
```
The name of the library is `libduktape.so.207.20700`:
```php title="SheetJSDuk.php (change highlighted line)"
// highlight-next-line
$sofile = './libduktape.so.207.20700';
```
8) Run the script:
```bash
php SheetJSDuk.php pres.numbers
```
If the program succeeded, the CSV contents will be printed to console and the
file `sheetjsw.xlsb` will be created. That file can be opened with Excel.
### Python
There is no official Python binding to the Duktape library. Instead, this demo
uses the raw `ctypes` interface[^2] to the Duktape shared library.
#### Python Demo
:::note Tested Deployments
This demo was tested in the following deployments:
| Architecture | Version | Python | Date |
|:-------------|:--------|:---------|:-----------|
| `darwin-x64` | `2.7.0` | `3.12.2` | 2024-03-15 |
| `darwin-arm` | `2.7.0` | `3.11.7` | 2024-02-13 |
| `linux-x64` | `2.7.0` | `3.11.3` | 2024-03-21 |
:::
0) Ensure `python` is installed and available on the system path.
1) Build the Duktape shared library:
```bash
curl -LO https://duktape.org/duktape-2.7.0.tar.xz
tar -xJf duktape-2.7.0.tar.xz
cd duktape-2.7.0
make -f Makefile.sharedlibrary
cd ..
```
2) Copy the shared library to the current folder. When the demo was last tested,
the shared library file name differed by platform:
| OS | name |
|:-------|:--------------------------|
| Darwin | `libduktape.207.20700.so` |
| Linux | `libduktape.so.207.20700` |
```bash
cp duktape-*/libduktape.* .
```
3) Download the SheetJS Standalone script, shim script and test file. Move all
three files to the project directory:
{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
curl -LO https://sheetjs.com/pres.numbers`}
4) Download [`SheetJSDuk.py`](pathname:///duk/SheetJSDuk.py):
```bash
curl -LO https://docs.sheetjs.com/duk/SheetJSDuk.py
```
5) Edit the `SheetJSDuk.py` script.
The `lib` variable declares the path to the library:
```python title="SheetJSDuk.py (edit highlighted line)"
#!/usr/bin/env python3
# highlight-next-line
lib = "libduktape.207.20700.so"
```
The name of the library is `libduktape.207.20700.so`:
```python title="SheetJSDuk.py (change highlighted line)"
# highlight-next-line
lib = "libduktape.207.20700.so"
```
The name of the library is `libduktape.so.207.20700`:
```python title="SheetJSDuk.py (change highlighted line)"
# highlight-next-line
lib = "libduktape.so.207.20700"
```
6) Run the script:
```bash
python3 SheetJSDuk.py 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.
### Zig
:::caution Zig support is considered experimental.
Great open source software grows with user tests and reports. Any issues should
be reported to the Zig project for further diagnosis.
:::
#### Zig Compilation
The main Duktape code can be added to the Zig build pipeline.
:::note pass
The following explanation was verified against Zig 0.11.0.
:::
Due to restrictions in the Zig C integration, the path to the Duktape `src`
folder must be added to the include path list:
```zig title="build.zig"
const exe = b.addExecutable(.{
// ...
});
// highlight-start
// this line is required to make @cInclude("duktape.h") work
exe.addIncludePath(.{ .path = "duktape-2.7.0/src" });
// highlight-end
```
The `duktape.c` source file must be added to the build sequence. For Zig version
0.11.0, Duktape must be compiled with flags `-std=c99 -fno-sanitize=undefined`
and linked against `libc` and `libm`:
```zig title="build.zig"
const exe = b.addExecutable(.{
// ...
});
// highlight-start
exe.addCSourceFile(.{:
.file = .{ .path = "duktape-2.7.0/src/duktape.c" },
.flags = &.{ "-std=c99", "-fno-sanitize=undefined" }
});
exe.linkSystemLibrary("c");
exe.linkSystemLibrary("m");
// highlight-end
```
#### Zig Import
`duktape.h` can be imported using the `@cImport` directive:
```zig title="main.zig"
const duktape = @cImport({
@cInclude("duktape.h");
});
```
Once imported, many API functions can be referenced from the `duktape` scope.
For example, `duk_peval_string` in the C interface will be available to Zig code
using the name `duktape.duk_peval_string`.
It is strongly recommended to colocate allocations and cleanup methods using
`defer`. For example, a Duktape context is created with `duk_create_heap` and
destroyed with `duk_destroy_heap`. The latter call can be deferred:
```zig
const ctx = duktape.duk_create_heap(null, null, null, null, null);
defer _ = duktape.duk_destroy_heap(ctx);
```
#### Zig Translator Caveats
The Zig translator does not properly handle blingo `void` casts. For example,
`duk_eval_string_noresult` is a function-like macro defined in `duktape.h`:
```c title="duk_eval_string_noresult blingo"
#define duk_eval_string_noresult(ctx,src) \
((void) duk_eval_raw((ctx), (src), 0, 0 /*args*/ | DUK_COMPILE_EVAL | DUK_COMPILE_NOSOURCE | DUK_COMPILE_STRLEN | DUK_COMPILE_NORESULT | DUK_COMPILE_NOFILENAME))
```
The compiler will throw an error involving `anyopaque` (C `void`):
```
error: opaque return type 'anyopaque' not allowed
```
The blingo performs a `void` cast to suppress certain C compiler warnings. The
spiritual equivalent in Zig is to assign to `_`.
The `duk_eval_raw` method and each compile-time constant are available in the
`duktape` scope. A manual translation is shown below:
```zig
_ = duktape.duk_eval_raw(ctx, src, 0, 0 | duktape.DUK_COMPILE_EVAL | duktape.DUK_COMPILE_NOSOURCE | duktape.DUK_COMPILE_STRLEN | duktape.DUK_COMPILE_NORESULT | duktape.DUK_COMPILE_NOFILENAME);
```
#### Zig Demo
:::note Tested Deployments
This demo was tested in the following deployments:
| Architecture | Version | Zig | Date |
|:-------------|:--------|:---------|:-----------|
| `darwin-x64` | `2.7.0` | `0.11.0` | 2024-03-10 |
| `win10-x64` | `2.7.0` | `0.11.0` | 2024-03-10 |
| `linux-x64` | `2.7.0` | `0.11.0` | 2024-03-10 |
On Windows, due to incompatibilities between WSL and PowerShell, some commands
must be run in WSL Bash.
:::
0) Create a new project folder:
```bash
mkdir sheetjs-zig
cd sheetjs-zig
```
1) Download Zig 0.11.0 from and extract to the
project folder.
```bash
curl -LO https://ziglang.org/download/0.11.0/zig-macos-x86_64-0.11.0.tar.xz
tar -xzf zig-macos-x86_64-0.11.0.tar.xz
```
```bash
curl -LO https://ziglang.org/download/0.11.0/zig-linux-x86_64-0.11.0.tar.xz
xz -d zig-linux-x86_64-0.11.0.tar.xz
tar -xf zig-linux-x86_64-0.11.0.tar
```
:::note pass
The following commands should be run within WSL bash.
:::
```bash
curl -LO https://ziglang.org/download/0.11.0/zig-windows-x86_64-0.11.0.zip
unzip zig-windows-x86_64-0.11.0.zip
```
2) Initialize a project:
```bash
./zig-macos-x86_64-0.11.0/zig init-exe
```
```bash
./zig-linux-x86_64-0.11.0/zig init-exe
```
:::note pass
The following command should be run within Powershell.
:::
```bash
.\zig-windows-x86_64-0.11.0\zig.exe init-exe
```
3) Download the Duktape source and extract in the current directory. On Windows,
the commands should be run within WSL:
```bash
curl -LO https://duktape.org/duktape-2.7.0.tar.xz
tar -xJf duktape-2.7.0.tar.xz
```
4) Download the SheetJS Standalone script, shim script and test file. Move all
three files to the `src` subdirectory:
The following commands can be run within a shell on macOS and Linux. On Windows,
the commands should be run within WSL bash:
{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
curl -LO https://sheetjs.com/pres.numbers
mv *.js src`}
5) Add the highlighted lines to `build.zig` just after the `exe` definition:
```zig title="build.zig (add highlighted lines)"
const exe = b.addExecutable(.{
.name = "sheetjs-zig",
// In this case the main source file is merely a path, however, in more
// complicated build scripts, this could be a generated file.
.root_source_file = .{ .path = "src/main.zig" },
.target = target,
.optimize = optimize,
});
// highlight-start
exe.addCSourceFile(.{ .file = .{ .path = "duktape-2.7.0/src/duktape.c" }, .flags = &.{ "-std=c99", "-fno-sanitize=undefined" } });
exe.addIncludePath(.{ .path = "duktape-2.7.0/src" });
exe.linkSystemLibrary("c");
exe.linkSystemLibrary("m");
// highlight-end
```
6) Download [`main.zig`](pathname:///duk/main.zig) and replace `src/main.zig`.
The following command should be run in WSL bash or the macOS or Linux terminal:
```bash
curl -L -o src/main.zig https://docs.sheetjs.com/duk/main.zig
```
7) Build and run the program:
```bash
./zig-macos-x86_64-0.11.0/zig build run -- pres.numbers
```
```bash
./zig-linux-x86_64-0.11.0/zig build run -- pres.numbers
```
:::caution pass
On Arch Linux and HoloOS (Steam Deck), compilation may fail:
```
zig build-exe sheetjs-zig Debug native: error: error: unable to create compilation: LibCStdLibHeaderNotFound
```
`glibc` and `linux-api-headers` must be installed:
```bash
sudo pacman -Syu glibc linux-api-headers
```
:::
```bash
.\zig-windows-x86_64-0.11.0\zig.exe build run -- pres.numbers
```
This step builds and runs the program. The generated program will be placed in
the `zig-out/bin/` subdirectory.
It should display some metadata along with CSV rows from the first worksheet.
It will also generate `sheetjs.zig.xlsx`, which can be opened with a spreadsheet
editor such as Excel.
### Perl
The Perl binding for Duktape is available as `JavaScript::Duktape::XS` on CPAN.
The Perl binding does not have raw `Buffer` ops, so Base64 strings are used.
#### Perl Demo
:::note Tested Deployments
This demo was tested in the following deployments:
| Architecture | Version | Date |
|:-------------|:--------|:-----------|
| `darwin-x64` | `2.2.0` | 2024-03-15 |
| `darwin-arm` | `2.2.0` | 2024-02-13 |
| `linux-x64` | `2.2.0` | 2024-03-21 |
:::
0) Ensure `perl` and `cpan` are installed and available on the system path.
1) Install the `JavaScript::Duktape::XS` library:
```bash
cpan install JavaScript::Duktape::XS
```
:::note pass
On some systems, the command must be run as the root user:
```bash
sudo cpan install JavaScript::Duktape::XS
```
:::
2) Download [`SheetJSDuk.pl`](pathname:///duk/SheetJSDuk.pl):
```bash
curl -LO https://docs.sheetjs.com/duk/SheetJSDuk.pl
```
3) Download the SheetJS ExtendScript build and test file:
{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.extendscript.js
curl -LO https://sheetjs.com/pres.xlsx`}
4) Run the script:
```bash
perl SheetJSDuk.pl pres.xlsx
```
If the script succeeded, the data in the test file will be printed in CSV rows.
The script will also export `SheetJSDuk.xlsb`.
:::note pass
In some test runs, the command failed due to missing `File::Slurp`:
```
Can't locate File/Slurp.pm in @INC (you may need to install the File::Slurp module)
```
The fix is to install `File::Slurp` with `cpan`:
```bash
sudo cpan install File::Slurp
```
:::
[^1]: See [Foreign Function Interface](https://www.php.net/manual/en/book.ffi.php) in the PHP documentation.
[^2]: See [`ctypes`](https://docs.python.org/3/library/ctypes.html) in the Python documentation.