ffi-swig generating a :string instead of a :pointer

[stepheneb]

See: http://groups.google.com/group/ruby-ffi/browse_thread/thread/98eaf51ab0386347

I have a C++ function that takes a pointer to a buffer where the function stores a C-string.

This is what I wrote and got working.

attach_function :GoIO_GetNthAvailableDeviceName, [:pointer, :int, :int, :int, :int], :int

However if I use ffi-swig it generates a :string as the first parameter.

attach_function :GoIO_GetNthAvailableDeviceName, [ :string, :int, :int, :int, :int ], :int

Is there anyway this could work? The function needs an address to a location to store a C-string.

Here's the C++ function:

GOIO_DLL_INTERFACE_DECL gtype_int32 GoIO_GetNthAvailableDeviceName(
  char *pBuf,            // [out] ptr to buffer to store device name string.
  gtype_int32 bufSize,   // [in] number of bytes in buffer pointed to by pBuf.
                         // Strlen(pBuf) < bufSize, because the string is NULL terminated.
  gtype_int32 vendorId,  // [in] USB vendor id
  gtype_int32 productId, //[in] USB product id
  gtype_int32 N);        //[in] index into list of known devices, 0 => first device in list.

Looking more closely at ffi-swig it's type_spec.rb does expect:

char *string;

to be turned into a :string.

I'm not much of a C programmer but is that correct? It seems in this case it should be a pointer.

Types like these are correctly turned into :string

const char *string;

The choice about turning a pointer into a string appears to be made in ffi-swig at lib/generator/type.rb:74:

def pointer
  if @declaration.is_pointer? or @is_pointer > 0
    @is_pointer += 1
    if @full_decl.scan(/^p\.(.+)/).flatten[0]
      ffi_type_from(@full_decl.scan(/^p\.(.+)/).flatten[0])
    elsif @full_decl == 'char' and @is_pointer == 2
      ':string'
    else
      ':pointer'
    end
  end       
end