Exit Zen
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Less total memory is required to process the full input
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To use the <<ref_stream_parser>>, declare an instance. Then call <<ref_stream_parser_write>> zero or more times with successive buffers representing the input JSON. When there are no more buffers, call <<ref_stream_parser_finish>>. The function <<ref_stream_parser_done>> returns `true` after a successful call to `write` or `finish` if parsing is complete.
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In the following example a JSON text is parsed from standard input a line at a time. Error codes are used instead. The function <<ref_stream_parser_finish>> is used to indicate the end of the input:
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This example will break, if comments are enabled, because of
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`std::getline` use (see the warning in <<non_standard_json>> section).
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We can complicate the example further by extracting _several_ JSON values from the sequence of lines.
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Controlling Memory
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After default construction, or after <<ref_stream_parser_reset>> is called with no arguments, the <<ref_value>> produced after a successful parse operation uses the default memory resource. To use a different memory resource, call `reset` with the resource to use. Here we use a <<ref_monotonic_resource>>, which is optimized for parsing but not subsequent modification:
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To achieve performance and memory efficiency, the parser uses a temporary storage area to hold intermediate results. This storage is reused when parsing more than one JSON text, reducing the total number of calls to allocate memory and thus improving performance. Upon construction, the memory resource used to perform allocations for this temporary storage area may be specified. Otherwise, the default memory resource is used. In addition to a memory resource, the parser can make use of a caller-owned buffer for temporary storage. This can help avoid dynamic allocations for small inputs. The following example uses a four kilobyte temporary buffer for the parser, and falls back to the default memory resource if needed:
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Avoiding Dynamic Allocations
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Through careful specification of buffers and memory resources, it is possible to eliminate all dynamic allocation completely when parsing JSON, for the case where the entire JSON text is available in a single character buffer, as shown here:
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Custom Parsers
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Users who wish to implement custom parsing strategies may create their own handler to use with an instance of <<ref_basic_parser>>. The handler implements the function signatures required by SAX event interface. In <<examples_validate>> example we define the "null" parser, which throws out the parsed results, to use in the implementation of a function that determines if a JSON text is valid.
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