[#BloombergLP-baljsn-Decoder]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/baljsn.adoc[baljsn]::Decoder
:relfileprefix: ../../
:mrdocs:

This class provides a mechanism for decoding JSON data into value‐semantic objects. The `decode` methods are function templates that will decode any object that meets the requirements of a sequence, choice, or array object as defined in the `bdlat_sequencefunctions`, `bdlat_choicefunctions`, and `bdlat_choicefunctions` components respectively. These generic frameworks provide a common compile‐time interface for manipulating struct‐like and union‐like objects. In particular, the types generated by `bas_codegen.pl` provide the necessary interface and can be decoded using this component.

== Synopsis

Declared in `<baljsn_decoder.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class Decoder;
----

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/baljsn/Decoder/2constructor.adoc[`Decoder`]         [.small]#[constructor]#
| Construct a decoder object using the optionally specified `basicAllocator`. If `basicAllocator` is 0, the default allocator is used.
| xref:BloombergLP/baljsn/Decoder/decode-04.adoc[`decode`] 
| `decode` overloads
| xref:BloombergLP/baljsn/Decoder/decodeAny-038.adoc[`decodeAny`] 
| `decodeAny` overloads
| xref:BloombergLP/baljsn/Decoder/loggedMessages.adoc[`loggedMessages`] 
| Return a string containing any error, warning, or trace messages that were logged during the last call to the `decode` method. The log is reset each time `decode` is called.
| xref:BloombergLP/baljsn/Decoder/numUnknownElementsSkipped.adoc[`numUnknownElementsSkipped`] 
| Return the number of unknown elements that were skipped during the previous decoding operation. Note that unknown elements are skipped only if `options.skipUnknownElements() == true`.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:BloombergLP/baljsn/Decoder_ElementVisitor.adoc[BloombergLP::baljsn::Decoder_ElementVisitor]`
| This `class` implements a visitor for decoding elements within a sequence, choice, or array type. This is a component‐private class and should not be used outside of this component. Note that the operators provided in this `class` match the function signatures required of visitors decoding into elements of compatible types.
| `xref:BloombergLP/baljsn/Decoder_DecodeImpProxy.adoc[BloombergLP::baljsn::Decoder_DecodeImpProxy]`
| This class provides a functor that dispatches the appropriate `decodeImp` method for a `bdeat` Dynamic type. Note that the operators provided in this `class` match the function signatures required of visitors decoding into compatible types.
|===


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