$3

`c
#include "stdlib/napi/argv_float64array.h"
`

#### stdlib_napi_argv_float64array( env, value, \\data, \length, \message, \*err )

Converts a Node-API value to a double-precision floating-point array.

`c
#include "stdlib/napi/argv_float64array.h"
#include
#include

static napi_value addon( napi_env env, napi_callback_info info ) {
napi_value value;

// ...

double *X;
int64_t len;
napi_value err;
napi_status status = stdlib_napi_argv_float64array( env, value, &X, &len, "Must be a typed array.", &err );
assert( status == napi_ok );
if ( err != NULL ) {
assert( napi_throw( env, err ) == napi_ok );
return NULL;
}

// ...
}
`

The function accepts the following arguments:

- env: [in] napi_env environment under which the function is invoked.
- value: [in] napi_value Node-API value.
- data: [out] double** pointer for returning a reference to the output array.
- length: [out] int64_t* pointer for returning the number of array elements.
- message: [in] char* error message.
- err: [out] napi_value* pointer for storing a JavaScript error. If not provided a number, the function sets err with a JavaScript error; otherwise, err is set to NULL.

`c
napi_status stdlib_napi_argv_float64array( const napi_env env, const napi_value value, double *data, int64_t length, const char message, napi_value err );
`

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

#### STDLIB_NAPI_ARGV_FLOAT64ARRAY( env, X, len, argv, index )

Macro for converting an add-on callback argument to a double-precision floating-point array.

`c
#include "stdlib/napi/argv_float64array.h"
#include "stdlib/napi/argv.h"
#include
#include

static void fcn( const double X, const int64_t xlen, double Y, const int64_t ylen ) {
int64_t len;
int64_t i;

if ( xlen > ylen ) {
len = ylen;
} else {
len = xlen;
}
for ( i = 0; i < len; i++ ) {
Y[ i ] = X[ i ];
}
}

// ...

static napi_value addon( napi_env env, napi_callback_info info ) {
// Retrieve add-on callback arguments:
STDLIB_NAPI_ARGV( env, info, argv, argc, 2 );

// Convert the first argument to a C type:
STDLIB_NAPI_ARGV_FLOAT64ARRAY( env, X, xlen, argv, 0 );

// Convert the second argument to a C type:
STDLIB_NAPI_ARGV_FLOAT64ARRAY( env, Y, ylen, argv, 1 );

// ...

fcn( X, xlen, Y, ylen );
}
`

The macro expects the following arguments:

- env: environment under which the callback is invoked.
- X: output variable name for the array.
- len: output variable name for the array length.
- argv: name of the variable containing add-on callback arguments.
- index: argument index.