@stdlib/napi/argv/README.md

C APIs for creating Node-API native add-ons.

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# argv

> C utilities for retrieving Node-API add-on callback arguments.

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## Usage

```javascript
var headerDir = require( '@stdlib/napi/argv' );
```

#### 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/napi/argv' );

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

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* * *

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## C APIs

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### Usage

```c
#include "stdlib/napi/argv.h"
```

#### STDLIB_NAPI_ARGV( env, info, argv, argc, nargs )

Macro for retrieving add-on callback arguments.

```c
#include <node_api.h>

// ...

static napi_value addon( napi_env env, napi_callback_info info ) {
    // Retrieve callback arguments:
    STDLIB_NAPI_ARGV( env, info, argv, argc, 6 );

    // ...
}
```

The macro expects the following arguments:

-   **env**: environment under which the callback is invoked.
-   **info**: callback data.
-   **argv**: variable name for storing argument values.
-   **argc**: variable name for storing the number of provided arguments.
-   **nargs**: expected number of arguments.

If the number of provided arguments does **not** equal the expected number of arguments, the macro's generated code raises an exception.

#### STDLIB_NAPI_ARGV_INDEX2ORDINAL( index )

Macro for converting an index to an ordinal numeral.

```c
STDLIB_NAPI_ARGV_INDEX2ORDINAL( 2 )
```

The macro expects the following arguments:

-   **index**: argument index value.

The first few ordinal numerals are as follows:

-   `STDLIB_NAPI_ARGV_INDEX2ORDINAL( 0 )`: "First".
-   `STDLIB_NAPI_ARGV_INDEX2ORDINAL( 1 )`: "Second".
-   `STDLIB_NAPI_ARGV_INDEX2ORDINAL( 2 )`: "Third".
-   `STDLIB_NAPI_ARGV_INDEX2ORDINAL( 3 )`: "Fourth".
-   `STDLIB_NAPI_ARGV_INDEX2ORDINAL( 4 )`: "Fifth".
-   ...
-   `STDLIB_NAPI_ARGV_INDEX2ORDINAL( 29 )`: "Thirtieth".

This macro can be useful when generating error messages which state which argument is invalid (e.g., "invalid argument. **First** argument must be a number." ).

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