mirror of
https://github.com/nlohmann/json.git
synced 2026-10-07 15:07:13 +00:00
Niels Lohmann
759dd2e1b1
Add json_document and json_view, a read-only, zero-copy index of a JSON text, as the first public slice of the zero-copy view (#5295). A parse produces a flat array of 16-byte nodes in document order, one per value and one per object key. Strings stay in the source text; escaped strings are decoded into an arena. Integers are converted while their digits are in the cache; floats keep only their digit layout and are converted on read. Containers store the size of their subtree, so a reader can step over one in constant time. A document makes a handful of allocations, however many values it has. The parser accepts exactly what json::parse accepts, with every combination of ignore_comments and ignore_trailing_commas, with and without a trailing NUL, and under JSON_STRICT_NUL_HANDLING. It is portable C++11 and does not depend on byte order. basic_json_document adds parse, parse_copy, accept, read (reuses a document's memory), root, is_discarded, source, owns_source, node_count, memory_usage, and shrink_to_fit. basic_json_view adds type, the is_* queries, operator bool, size, empty, materialize, and source_offset. A parse error throws the same exception basic_json::parse would throw for the same input, message and position included. detail::abi_config keeps JSON_STRICT_NUL_HANDLING and JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON readable after json.hpp undefines them, in the ABI namespace so they always match the basic_json in use. A NUL byte that ends a // comment is the end of the input, as in parse() since #5696. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
114 lines
3.0 KiB
C++
114 lines
3.0 KiB
C++
// __ _____ _____ _____
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// __| | __| | | | JSON for Modern C++
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// | | |__ | | | | | | version 3.12.0
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// |_____|_____|_____|_|___| https://github.com/nlohmann/json
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//
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// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
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// SPDX-License-Identifier: MIT
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#pragma once
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#include <algorithm> // min
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#include <cstddef> // size_t
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#include <cstring> // memcmp, strlen
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#include <string> // basic_string
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#include <nlohmann/json.hpp>
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#include <nlohmann/detail/view/macro_scope.hpp>
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#if NLOHMANN_VIEW_HAS_CPP_17
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#include <string_view> // string_view
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#endif
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#ifndef JSON_NO_IO
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#include <ostream> // ostream
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#endif
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NLOHMANN_JSON_NAMESPACE_BEGIN
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namespace detail
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{
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namespace view
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{
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#if NLOHMANN_VIEW_HAS_CPP_17
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using string_ref = std::string_view;
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#else
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/// minimal C++11 stand-in for std::string_view
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class string_ref
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{
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public:
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using size_type = std::size_t;
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using const_iterator = const char*;
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string_ref() noexcept = default;
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// s must be null-terminated, as for std::string_view(const char*)
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// flawfinder: ignore
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string_ref(const char* s) : m_data(s), m_size(std::strlen(s)) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
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string_ref(const char* s, std::size_t n) noexcept : m_data(s), m_size(n) {}
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template<typename Traits, typename Alloc>
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string_ref(const std::basic_string<char, Traits, Alloc>& s) noexcept : m_data(s.data()), m_size(s.size()) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
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const char* data() const noexcept
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{
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return m_data;
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}
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std::size_t size() const noexcept
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{
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return m_size;
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}
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std::size_t length() const noexcept
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{
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return m_size;
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}
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bool empty() const noexcept
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{
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return m_size == 0;
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}
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const char* begin() const noexcept
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{
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return m_data;
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}
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const char* end() const noexcept
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{
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return m_data + m_size;
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}
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char operator[](std::size_t i) const noexcept
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{
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return m_data[i];
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}
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template<typename Traits, typename Alloc>
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explicit operator std::basic_string<char, Traits, Alloc>() const
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{
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return std::basic_string<char, Traits, Alloc>(m_data, m_size);
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}
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friend bool operator==(string_ref a, string_ref b) noexcept
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{
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return a.m_size == b.m_size && (a.m_size == 0 || std::memcmp(a.m_data, b.m_data, a.m_size) == 0);
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}
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friend bool operator!=(string_ref a, string_ref b) noexcept
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{
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return !(a == b);
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}
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friend bool operator<(string_ref a, string_ref b) noexcept
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{
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const int c = std::memcmp(a.m_data, b.m_data, (std::min)(a.m_size, b.m_size));
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return c != 0 ? c < 0 : a.m_size < b.m_size;
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}
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#ifndef JSON_NO_IO
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friend std::ostream& operator<<(std::ostream& o, string_ref s)
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{
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return o.write(s.m_data, static_cast<std::streamsize>(s.m_size));
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}
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#endif
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private:
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const char* m_data = "";
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std::size_t m_size = 0;
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};
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#endif
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} // namespace view
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} // namespace detail
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NLOHMANN_JSON_NAMESPACE_END
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