You can check if a channel exists (and if it does, find out its type)
by calling csoundGetChannelPtr() with a zero type value. It will then
fail, and either return CSOUND_ERROR if the channel does not exist yet,
or the type (in the same format as the type argument) of the already
existing channel.

On Saturday 24 June 2006 13:39, Rory Walsh wrote:

> I am trying to add more functionality to the GUI controls provided by 
> lettuce by allowing for two-way communication between Csound and the 
> host app's that Lettuce can generate. I would like for example to allow 
> users to be able to change a label in their host application by calling 
> *chnset* in Csound. The following line of code will create a label in 
> the host app with a default value of "caption"
> 
> label "chanName", width, height, top, left, "caption", "colour"
> 
> I would like if "caption" would remain the label text *until* chnset is 
> called in Csound. As it stands each host app has a timer that keeps 
> calling GetValueOutChannel(see below), which in turn calls 
> csoundGetChannelPtr(), which then sends data to the label channel which 
> in turn overwrites "caption". The main issue here is that 
> csoundGetChannelPtr() will create the channel is it does not already 
> exist, and it seems to initialise it to 0. In my timer function(see 
> below) I was doing a simple test, if(GetValueOutChannel()!=0) then 
> update label, but as you can imagine this didn't work so well 
> considering users would often like to send 0 to the label. So my 
> question is how can I prevent data from being sent on a particular 
> software channel until a call is made to *chnset*? I hope I have 
> explained my self well, has anyone any suggestions?

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