[Rails] Re: bug in fiddle or something I did is wrong?

Ruby on Rails Monday, November 23, 2015

On Monday, November 23, 2015 at 3:25:07 PM UTC, Liz Huang wrote:


Thanks!

Strange that I am able to get error message before just using char *, thought
it meant passing string by pointer already.

it does, but if you want to allocate a new buffer and have the caller access that then you need pointer to a pointer
 
I change the argument to char ** errMsg, but in Ruby, when I tried to
convert the pointer to string, I got error message:

[snip]
 
      if options.is_a?(::JSON::State)  
        # Called from JSON.{generate,dump}, forward it to JSON gem's to_json  
        self.to_json_without_active_support_encoder(options)  
      else  
        # to_json is being invoked directly, use ActiveSupport's encoder  
        ActiveSupport::JSON.encode(self, options)
Do I need to  change anything in ruby file when use a pointer?


Yes. You need to allocate a pointer size bit of memory for the C function (via Fiddle::Pointer). The C function fills that in, you then use the ptr method on Fiddle::Pointer to get the memory allocated by the C function, and create your string from there. (don't forget to free the memory too)

Fred

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Posted by Ruby on Rails at 9:21 AM

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