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https://github.com/nlohmann/json.git
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Niels Lohmann
4303ba674d
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>
65 lines
2.3 KiB
C++
65 lines
2.3 KiB
C++
// __ _____ _____ _____
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// __| | __| | | | JSON for Modern C++ (supporting code)
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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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import std;
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import nlohmann.json;
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using namespace nlohmann::literals;
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// Exercise the surface exported by the nlohmann.json module so that a missing
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// or broken export is caught at compile time.
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//
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// Standard-library facilities are pulled in via `import std;` rather than
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// textual `#include`s: mixing `import` with textual standard headers does not
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// compile under GCC's C++20 modules implementation, whereas `import std;` works
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// across GCC, Clang, and MSVC. This requires C++23 and CMake's (experimental)
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// import-std support; see CMakeLists.txt.
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int main()
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{
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// basic_json / json: parsing and value access
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nlohmann::json j = nlohmann::json::parse(R"({"a": 1, "list": [1, 2, 3]})");
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const int a = j["a"].get<int>();
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// json_pointer and operator""_json_pointer
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nlohmann::json_pointer<std::string> ptr = "/list/2"_json_pointer;
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const int last = j[ptr].get<int>();
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// operator""_json literal
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const nlohmann::json lit = R"([1, 2, 3])"_json;
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// ordered_json
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nlohmann::ordered_json oj;
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oj["b"] = 2;
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const int b = oj["b"].get<int>();
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// ordered_map alias
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nlohmann::ordered_map<std::string, int> m;
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m["x"] = 1;
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// adl_serializer (reference the exported template)
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using serializer = nlohmann::adl_serializer<int, void>;
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static_cast<void>(sizeof(serializer));
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// to_string
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const std::string dumped = nlohmann::to_string(j);
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// operator<< (hidden friend, reached via ADL through the module)
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std::ostringstream os;
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os << j << oj << lit;
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// json_document / json_view (json_view.hpp): zero-copy parse of a literal
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const nlohmann::json_document doc = nlohmann::json_document::parse(R"({"a": 1, "list": [1, 2, 3]})");
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const std::size_t doc_size = doc.root().size();
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// use every result so the references cannot be optimized away
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return (a == 1 && last == 3 && b == 2 && lit.size() == 3
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&& m.size() == 1 && !dumped.empty() && !os.str().empty()
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&& doc_size == 2)
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? 0 : 1;
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}
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