$3

`c
#include "stdlib/napi/argv_strided_float64array.h"
`

#### stdlib_napi_argv_strided_float64array( env, N, stride, value, \\data, \message1, \message2, \*err )

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

`c
#include "stdlib/napi/argv_strided_float64array.h"
#include
#include

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

// ...

int64_t N = 100;
int64_t stride = 1;

// ...

double *X;
napi_value err;
napi_status status = stdlib_napi_argv_strided_float64array( env, N, stride, value, &X, "Must be a typed array.", "Must have sufficient elements.", &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.
- N: [in] int64_t number of indexed elements.
- stride: [in] int64_t stride length.
- value: [in] napi_value Node-API value.
- data: [out] double** pointer for returning a reference to the output array.
- message1: [in] char* error message if a value is not a Float64Array.
- message2: [in] char* error message if a value has insufficient elements.
- 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_strided_float64array( const napi_env env, const int64_t N, const int64_t stride, const napi_value value, double *data, const char message1, const char message2, napi_value err );
`

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

#### STDLIB_NAPI_ARGV_STRIDED_FLOAT64ARRAY( env, X, N, stride, argv, index )

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

`c
#include "stdlib/napi/argv_strided_float64array.h"
#include "stdlib/napi_argv_int64.h"
#include "stdlib/napi/argv.h"
#include
#include

static void fcn( const int64_t N, const double X, const int64_t strideX, double Y, const int64_t strideY ) {
int64_t i;
for ( i = 0; i < N; i++ ) {
Y[ istrideY ] = X[ istrideX ];
}
}

// ...

static napi_value addon( napi_env env, napi_callback_info info ) {
// Retrieve add-on callback arguments:
STDLIB_NAPI_ARGV( env, info, argv, argc, 5 );

// Convert the number of indexed elements to a C type:
STDLIB_NAPI_ARGV_INT64( env, N, argv, 0 );

// Convert the stride arguments to C types:
STDLIB_NAPI_ARGV_INT64( env, strideX, argv, 2 );
STDLIB_NAPI_ARGV_INT64( env, strideY, argv, 4 );

// Convert the arrays a C types:
STDLIB_NAPI_ARGV_STRIDED_FLOAT64ARRAY( env, X, N, strideX, argv, 1 );
STDLIB_NAPI_ARGV_STRIDED_FLOAT64ARRAY( env, Y, N, strideY, argv, 3 );

// ...

fcn( N, X, strideX, Y, strideY );
}
`

The macro expects the following arguments:

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