115 lines
3.3 KiB
Markdown
115 lines
3.3 KiB
Markdown
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# DDL Decoder/Codec {#page_codec}
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# Accessing Data with a Decoder/Codec
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Let's take a look at a basic structure:
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````xml
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<struct alignment="4" name="tTest" version="1" ddlversion="2.0">
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<element name="bBool" type="tBool" arraysize="1">
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<serialized byteorder="LE" bytepos="0" bitpos="0" numbits="8"/>
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<deserialized alignment="1"/>
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</element>
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<element name="nInt8" type="tInt8" arraysize="1">
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<serialized byteorder="LE" bytepos="1" bitpos="0" numbits="8"/>
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<deserialized alignment="1"/>
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</element>
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<element name="nUInt32" type="tUInt32" arraysize="1">
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<serialized byteorder="LE" bytepos="2" bitpos="0" numbits="32"/>
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<deserialized alignment="4"/>
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</element>
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<element name="fFloat32" type="tFloat32" arraysize="1">
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<serialized byteorder="LE" bytepos="6" bitpos="0" numbits="32"/>
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<deserialized alignment="4"/>
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</element>
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</struct>
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````
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# Decoding
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Read access is handled with the ddl::Decoder class:
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````cpp
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tFloat64 readData(const void* const_data, size_t data_size)
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{
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// this should of course be cached (as a member etc.)
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ddl::CodecFactory factory("tTest", "<adtf:ddl>....");
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auto decoder = factory.makeDecoderFor(const_data, data_size);
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adtf_util::cVariant value;
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// for name based lookup use the access_element namespace
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{
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value = ddl::access_element::get_value(decoder, "fFloat32");
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}
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// alternativley you can of course use indexed based lookup
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{
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decoder.getElementValue(3, value);
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}
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return value;
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}
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````
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# Encoding
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Write access is handled with the ddl::Codec class:
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````cpp
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void writeData(void* data, size_t data_size, tFloat64 value)
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{
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// this should of course be cached (as a member etc.)
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ddl::CodecFactory factory("tTest", "<adtf:ddl>....");
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auto codec = factory.makeCodecFor(data, data_size);
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// name based lookup
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ddl::access_element::set_value(codec, "fFloat32", value);
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// or index based
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codec.setElementValue(3, value);
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}
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````
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# Selecting the Data Representation
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By default decoders/codecs are created for the deserialized representation.
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To create them for the serialized representation pass the correct parameters to the make... methods.
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````cpp
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auto decoder = factory.makeDecoderFor(const_data, data_size,
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DataRepresentation::serialized);
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````
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# Inspection
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You can inspect the struct handled by a decoder/codec with the help of ddl::StaticDecoder::getElement:
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````cpp
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void dumstruct_elements(const ddl::StaticDecoder& decoder)
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{
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for (size_t element = 0; element < decoder.getElementCount(); ++element)
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{
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const ddl::StructElement* struct_element;
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decoder.GetElement(element, struct_element);
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std::cout << struct_element->strName << std::endl;
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}
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}
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````
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# Transformation
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Converting between the representations can be done with ddl::serialization::transform:
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````cpp
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tSize serialized_size = decoder.getBufferSize(ddl::DataRepresentation::serialized);
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uint8_t* buffer = new uint8_t[serialized_size];
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auto Codec = decoder.makeCodecFor(buffer, serialized_size, ddl::DataRepresentation::serialized);
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ddl::serialization::transform(decoder, codec);
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````
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There is also a convienence method ddl::serialization::transform_to_buffer that handles the allocation of memory for you with the help of an adtf_util::cMemoryBlock.
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