Exit Zen
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Allocator Propagation
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We can complicate the example further by extracting _several_ JSON values from the sequence of lines.
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147KB
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The result is constructed from two pointers to `const char`.
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Boost.JSON has been tested with the following compilers:
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<<ref_value_try_as_uint64>>
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The containers <<ref_array>>, <<ref_object>>, and <<ref_value>> all propagate the memory resource they were constructed with to child elements:
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Controlling Memory
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A array containing only floating-point numbers.
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For composite types (sequences, tuples, described classes, etc.) conversion of contained objects is applied recursively. For example:
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clang: 3.5, 3.6, 3.7, 3.8, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
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<<ref_value_as_uint64>>
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This propagation acts recursively, containers within containers will all have the resource propagated. Once a container is constructed, its memory resource can never be changed.
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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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<<parse_random_json,*random.json*>>
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Here, the map is converted into an <<ref_object>>, since it matches <<ref_is_map_like>>. Each of its keys is converted into a <<ref_string>>, as `std::string` matches <<ref_is_string_like>>, and each of its values is converted into an <<ref_array>>, as `std::pair` matches <<ref_is_tuple_like>>. Finally, elements of pairs are converted into a `std::int64_t` number and a `bool`.
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gcc: 4.8, 4.9, 5, 6, 7, 8, 9, 10, 11, 12
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<<ref_value_get_uint64>>
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Resource Lifetime
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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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