Returning structs in emscripten

Jan 24, 2015

Based on the discussion over here, I’ve created a simple code sample.

C code:

typedef struct shift_addition_data_s
{
	float sindelta;
	float cosdelta;
	float rate;
} shift_addition_data_t;

shift_addition_data_t shift_addition_init(float rate)
{
	rate*=2;
	shift_addition_data_t out;
	out.sindelta=sin(rate*PI);
	out.cosdelta=cos(rate*PI);
	out.rate=rate;
	return out;
}

How to call it from JavaScript:

function test_struct_return_value()
{
	v=STACKTOP;
	STACKTOP+=4*3;
	_shift_addition_init(v,0.2);
	console.log( 
		"sinval=", getValue(v,'float'), 
		"cosval=", getValue(v+4,'float'), 
		"rate=", getValue(v+8,'float') 
	);
	STACKTOP=v;
}

Note that we had to pass v to _shift_addition_init.
Thanks for the guys on the list for figuring this out.

The source of this post is my previous blog at HA5KFU.