37 lines
1.1 KiB
Ruby
37 lines
1.1 KiB
Ruby
# query.rb
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require 'fiddle'
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# Look for a C variable named QueryPointer.
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# Raise an error if it is missing.
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c_var = Fiddle.dlopen(nil)['QueryPointer']
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int = Fiddle::TYPE_INT
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voidp = Fiddle::TYPE_VOIDP
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sz_voidp = Fiddle::SIZEOF_VOIDP
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# Implement the C function
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# int Query(void *data, size_t *length)
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# in Ruby code. Store it in a global constant in Ruby (named Query)
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# to protect it from Ruby's garbage collector.
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#
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Query = Fiddle::Closure::BlockCaller
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.new(int, [voidp, voidp]) do |datap, lengthp|
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message = "Here am I"
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# We got datap and lengthp as Fiddle::Pointer objects.
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# Read length, assuming sizeof(size_t) == sizeof(void *).
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length = lengthp[0, sz_voidp].unpack('J').first
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# Does the message fit in length bytes?
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if length < message.bytesize
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0 # failure
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else
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length = message.bytesize
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datap[0, length] = message # Copy the message.
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lengthp[0, sz_voidp] = [length].pack('J') # Update the length.
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1 # success
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end
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end
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# Set the C variable to our Query.
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Fiddle::Pointer.new(c_var)[0, sz_voidp] = [Query.to_i].pack('J')
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