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# Add-on Arguments

> C API for validating, extracting, and transforming (to native C types) function arguments provided to an ndarray Node-API add-on interface.

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## Usage

```javascript
var headerDir = require( '@stdlib/ndarray/base/napi/addon-arguments' );
```

#### headerDir

Absolute file path for the directory containing header files for C APIs.

```javascript
var dir = headerDir;
// returns <string>
```

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## Examples

```javascript
var headerDir = require( '@stdlib/ndarray/base/napi/addon-arguments' );

console.log( headerDir );
// => <string>
```

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* * *

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## C APIs

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### Usage

```c
#include "stdlib/ndarray/base/napi/addon_arguments.h"
```

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#### stdlib_ndarray_napi_addon_arguments( env, argv, nargs, nin, \*arrays\[], \*err )

Validates, extracts, and transforms (to native C types) function arguments provided to an ndarray Node-API add-on interface.

```c
#include <node_api.h>
#include <stdint.h>
#include <assert.h>

// ...

/**
* Receives JavaScript callback invocation data.
*
* @param env    environment under which the function is invoked
* @param info   callback data
* @return       Node-API value
*/
napi_value addon( napi_env env, napi_callback_info info ) {
    napi_status status;

    // ...

    int64_t nargs = 6;
    int64_t nin = 2;

    // Get callback arguments:
    size_t argc = 6;
    napi_value argv[ 6 ];
    status = napi_get_cb_info( env, info, &argc, argv, nullptr, nullptr );
    assert( status == napi_ok );

    // ...

    // Process the provided arguments:
    struct ndarray *arrays[ 3 ];

    napi_value err;
    status = stdlib_ndarray_napi_addon_arguments( env, argv, nargs, nin, arrays, &err );
    assert( status == napi_ok );

    // ...

}

// ...
```

The function accepts the following arguments:

-   **env**: `[in] napi_env` environment under which the function is invoked.
-   **argv**: `[in] napi_value*` ndarray function arguments.
-   **nargs**: `[in] int64_t` total number of expected arguments.
-   **nin**: `[in] int64_t` number of input ndarray arguments.
-   **arrays**: `[out] struct ndarrays**` destination array for storing pointers to both input and output ndarrays.
-   **err**: `[out] napi_value*` pointer for storing a JavaScript error.

```c
napi_status stdlib_ndarray_napi_addon_arguments( const napi_env env, const napi_value *argv, const int64_t nargs, const int64_t nin, struct ndarray *arrays[], napi_value *err );
```

The function returns a `napi_status` status code indicating success or failure (returns `napi_ok` if success).

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### Notes

-   The function assumes the following argument order:

    ```text
    [ ib1, im1, ib2, im2, ..., ob1, om1, ob2, om2, ... ]
    ```

    where

    -   `ib#` is a data buffer for an input ndarray.
    -   `im#` is meta data for an input ndarray.
    -   `ob#` is a data buffer for an output ndarray.
    -   `om#` is meta data for an output ndarray.

-   The function may return one of the following JavaScript errors:

    -   `Error`: unable to allocate memory when processing input ndarray.
    -   `Error`: unable to allocate memory when processing output ndarray.

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