How do I create a C Pointer in MacRuby?

Question

I am working with a C Framework in MacRuby which has a structure

int CPhidget_getSerialNumber(CPhidgetHandle phid,int * serialNumber)

You can see the full documentation here (if you are interested).

In MacRuby I have tried the following:

i = CPhidget_getSerialNumber(@encoder, nil)

The above gets me a number but not the serial number.

CPhidget_getSerialNumber(@encoder, i)

This gets me an error stating: expected instance of Pointer, got `0' (Fixnum) (TypeError) (which doesn't surprise me).

So my main question is: Is there an equivalent of a C Pointer in MacRuby?

The documentation you link to seems to be the documentation for the raw C library. How do you perform the foreign function calls? — Niklas B.
– Niklas B., Commented May 18, 2012 at 22:52
I have a cocoa framework based off the C-API. The functions are all the same (apparently). I generated a bridge support file to access the constants in the header file and it seems to be working. Here's the Cocoa 'guide' (phidgets.com/documentation/Tutorials/Getting_Started_Cocoa.pdf) — tsugua
– tsugua, Commented May 18, 2012 at 22:55

Josh · Accepted Answer · 2012-05-19 00:47:05Z

2

MacRuby has a Pointer class, which can stand in for a C pointer. So, you could do something like:

i = Pointer.new(:int)
CPhidget_getSerialNumber(@encoder, i)

Then, to extract the results from the pointer (i.e. dereference it), you use Ruby's array access syntax:

i[0] #=> value from CPhidget_getSerialNumber

answered May 19, 2012 at 0:47

Josh

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3 Comments

tsugua Over a year ago

Awesome, Thanks for your help Josh. I couldn't find any reference to the pointer class in Ruby docs or the Apple documentation. Just out of curiosity, do you know where the docs on it are?

Josh Over a year ago

It seems we haven't actually documented this yet (normally you'd be able to read the documentation using macri). If you'd like to file a bug requesting documentation, you can do so here: github.com/MacRuby/MacRuby/issues

tsugua Over a year ago

Hi Josh, I will file the bug but I did end up finding a pointer class reference on the github wiki: github.com/MacRuby/MacRuby/wiki/Pointer-Class

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