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Add json_document and json_view: node index, parser, and document
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>
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@@ -0,0 +1,403 @@
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// __ _____ _____ _____
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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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#include "doctest_compatibility.h"
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#include <nlohmann/json.hpp>
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#if JSON_TEST_USING_MULTIPLE_HEADERS
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#include <nlohmann/detail/view/builder.hpp>
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#include <nlohmann/detail/view/string_ref.hpp>
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#else
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#include <nlohmann/json_view.hpp> // the single header contains the internal headers
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#endif
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using nlohmann::json;
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#include <cstdint>
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#include <fstream>
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#include <map>
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#include <memory>
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#include <random>
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#include <sstream>
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#include <string>
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#include <utility>
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#include <vector>
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#include <test_data.hpp>
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namespace
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{
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using nlohmann::detail::view::document_data;
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using nlohmann::detail::view::node;
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// the node index of a text; a vector input has no terminating NUL, so that
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// AddressSanitizer catches any read past the last byte
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struct built
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{
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std::unique_ptr<document_data, document_data::deleter> data{}; // NOLINT(readability-redundant-member-init)
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std::vector<char> copy{}; // NOLINT(readability-redundant-member-init)
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bool ok = false;
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nlohmann::detail::view::parse_failure failure{};
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};
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template<typename FloatType = double>
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built build(const std::string& text, bool comments, bool trailing_commas, bool sentinel)
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{
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built r;
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r.data.reset(document_data::create(nlohmann::detail::view::estimate_nodes(text.data(), text.size())));
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const char* src = text.c_str();
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if (!sentinel)
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{
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r.copy.assign(text.begin(), text.end());
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src = r.copy.data();
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}
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r.ok = nlohmann::detail::view::build < FloatType, !nlohmann::detail::abi_config::strict_nul_handling > (*r.data, src, text.size(), comments, trailing_commas, sentinel, r.failure);
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r.data->src = src;
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r.data->base[0] = src;
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r.data->base[1] = r.data->arena.data();
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return r;
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}
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// the value of a subtree, as json::parse would build it
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json value_of(const document_data& d, const node*& n)
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{
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const node& x = *n;
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++n;
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switch (static_cast<json::value_t>(x.kind))
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{
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case json::value_t::object:
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{
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json o = json::object();
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const node* const end = &x + x.next;
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while (n != end)
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{
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const std::string key(d.str(*n), n->len);
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++n;
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o[key] = value_of(d, n);
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}
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return o;
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}
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case json::value_t::array:
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{
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json a = json::array();
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const node* const end = &x + x.next;
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while (n != end)
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{
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a.push_back(value_of(d, n));
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}
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return a;
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}
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case json::value_t::string:
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return std::string(d.str(x), x.len);
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case json::value_t::boolean:
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return (x.flags & nlohmann::detail::view::node_flags::is_true) != 0;
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case json::value_t::number_integer:
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return static_cast<std::int64_t>(nlohmann::detail::view::integer_bits(x));
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case json::value_t::number_unsigned:
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return nlohmann::detail::view::integer_bits(x);
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case json::value_t::number_float:
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return json::parse(std::string(d.src + x.off, x.len)).get<double>();
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case json::value_t::null:
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case json::value_t::binary:
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case json::value_t::discarded:
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default:
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return nullptr;
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}
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}
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json value_of(const built& b)
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{
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const node* n = b.data->tape;
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json v = value_of(*b.data, n);
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CHECK(n == b.data->tape + b.data->tape_size);
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return v;
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}
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// accept/reject and the value must match json::parse, for all options and
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// with and without a NUL after the text
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void check_same(const std::string& text)
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{
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CAPTURE(text)
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for (int options = 0; options < 4; ++options)
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{
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const bool comments = (options & 1) != 0;
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const bool trailing_commas = (options & 2) != 0;
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const bool accepted = json::accept(text, comments, trailing_commas);
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for (const bool sentinel :
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{
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true, false
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})
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{
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const built b = build(text, comments, trailing_commas, sentinel);
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CHECK(b.ok == accepted);
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if (b.ok && accepted)
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{
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CHECK(value_of(b) == json::parse(text, nullptr, true, comments, trailing_commas));
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}
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}
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}
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}
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// a small deterministic generator of documents
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struct generator
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{
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std::mt19937 rng{5295}; // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
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int r(int n)
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{
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return static_cast<int>(rng() % static_cast<unsigned>(n));
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}
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void ws(std::string& o)
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{
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for (int n = r(4) == 0 ? r(12) : r(2); n > 0; --n)
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{
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o += " \n\t\r "[r(6)];
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}
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}
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void str(std::string& o)
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{
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static const char* const pieces[] = {"a", "Z", " ", "~", "\\n", "\\\"", "\\\\", "\\/", "\\u00e9", "\\ud83d\\ude00", "\xc3\xa9", "\xe3\x81\x82", "\xf0\x9f\x98\x80", "\x7f", "\\u001f", "long enough text to leave the first 16 bytes"}; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
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o += '"';
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for (int n = r(3) == 0 ? r(20) : r(6); n > 0; --n)
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{
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o += pieces[r(16)];
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}
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o += '"';
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}
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void num(std::string& o)
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{
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static const char* const numbers[] = {"0", "-0", "1", "-1", "12", "123456789", "1234567890123456789", "9223372036854775807", "-9223372036854775808", // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
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"9223372036854775808", "18446744073709551615", "18446744073709551616", "-9223372036854775809",
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"1.5", "-2.25e-3", "1e10", "1E+2", "0.000001", "3.141592653589793238462643", "1e308", "-1e-400", "123.456e7"
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};
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o += numbers[r(22)];
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}
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void value(std::string& o, int depth)
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{
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ws(o);
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const int k = depth > 5 ? 2 + r(6) : r(8);
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if (k == 0 || k == 1)
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{
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const bool object = k == 0;
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o += object ? '{' : '[';
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for (int i = r(5); i > 0; --i)
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{
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ws(o);
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if (object)
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{
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str(o);
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ws(o);
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o += ':';
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}
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value(o, depth + 1);
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o += i > 1 ? "," : "";
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}
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ws(o);
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o += object ? '}' : ']';
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}
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else if (k < 4)
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{
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str(o);
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}
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else if (k < 6)
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{
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num(o);
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}
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else
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{
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static const char* const literals[] = {"true", "false", "null"}; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
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o += literals[r(3)];
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}
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ws(o);
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}
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};
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} // namespace
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TEST_CASE("json_view string_ref")
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{
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// std::string_view in C++17, a stand-in with the same members before
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using nlohmann::detail::view::string_ref;
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const std::string text = "abc";
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const string_ref r(text);
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CHECK(r.length() == 3);
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CHECK(std::string(r.begin(), r.end()) == "abc");
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CHECK(r[1] == 'b');
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CHECK(r != string_ref("abd"));
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CHECK_FALSE(r != string_ref("abcd", 3));
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std::ostringstream o;
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o << r;
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CHECK(o.str() == "abc");
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}
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TEST_CASE("json_view builder")
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{
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SECTION("scalars and containers")
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{
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for (const char* text :
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{
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"null", "true", "false", "0", "-0", "42", "-42", "1.5", "\"\"", "\"abc\"", "[]", "{}", "[1,2,3]", "{\"a\":1,\"b\":[true,null]}", // NOLINT(modernize-raw-string-literal)
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" [ 1 , 2 ] ", "{\"a\" : {\"b\" : {}}}", "[[[]]]", "\"\\u00e4\\n\\ud83d\\ude00\"", "{\"a\":1,\"a\":2}", "18446744073709551616", // NOLINT(modernize-raw-string-literal)
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"-9223372036854775809", "123456789012345678901234567890", "1e400", "-1e400", "1.7976931348623157e308"
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})
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{
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check_same(text);
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}
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// the midpoint between the largest double and 2^1024 rounds to
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// infinity (an overflow), one less to the largest double: with more
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// than 19 digits, Eisel-Lemire cannot decide these, and the overflow
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// check needs the exact comparison with the midpoint
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const std::string midpoint = "179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497792";
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const std::string below = "179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497791";
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check_same(midpoint);
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check_same("-" + midpoint);
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check_same(below);
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check_same("[" + below + "," + midpoint + "]");
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// the check uses the floating-point type of the document: with float,
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// the view rejects what parse() rejects (out_of_range.406), and a
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// double document is not affected
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using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
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CHECK_FALSE(float_json::accept("1e39"));
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CHECK(float_json::accept("3.4028235e38"));
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CHECK_FALSE(float_json::accept("3.4028236e38"));
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for (const char* text :
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{
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"1e39", "-1e39", "3.4028235e38", "-3.4028235e38", "3.4028236e38", "-3.4028236e38", "3.4028234663852886e38", "1e38",
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"340282356779733661637539395458142568448", "340282356779733661637539395458142568447.99", "0.00034028236e42",
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"[1.5e38, 3.5e38]", "{\"a\": 1e-50, \"b\": 1e39}"
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})
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{
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CAPTURE(text)
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const bool float_accepted = float_json::accept(text);
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for (const bool sentinel :
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{
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true, false
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})
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{
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const built f = build<float>(text, false, false, sentinel);
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CHECK(f.ok == float_accepted);
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if (!f.ok)
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{
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CHECK(f.failure.code == nlohmann::detail::view::error_code::number_overflow);
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}
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CHECK(build<double>(text, false, false, sentinel).ok == json::accept(text));
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}
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}
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}
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SECTION("malformed input")
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{
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for (const char* text :
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{
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"", " ", "[", "]", "{", "}", "[1,]", "{\"a\":1,}", "[1 2]", "{\"a\" 1}", "{1:2}", "tru", "nul", "fals", "truex", "-", "01", "1.", ".5", "1e", "1e+",
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"\"", "\"abc", "\"\\x\"", "\"\\u12\"", "\"\\u12G4\"", "\"\\ud800\"", "\"\\udc00\"", "\"\\ud800\\u0041\"", "\"\x01\"", "\"\xff\"", "\"\xc3\"", // NOLINT(modernize-raw-string-literal)
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"\"\xe0\x80\x80\"", "\"\xed\xa0\x80\"", "[1]x", "[1] [2]", "/", "/*", "/* */ 1", "// c\n1", "1 // c", "[1,/*c*/2]", "[1,2,]"
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})
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{
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check_same(text);
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}
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}
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SECTION("NUL, BOM, and whitespace")
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{
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// a NUL inside a string is a control character, as for json::parse
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// (where a NUL ends the input, it does so only between values)
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for (const bool sentinel :
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{
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true, false
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})
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{
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const built b = build(std::string("[\"ab\0cd\"]", 9), false, false, sentinel);
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CHECK(!b.ok);
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CHECK(b.failure.code == nlohmann::detail::view::error_code::string_control_character);
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CHECK(b.failure.offset == 4);
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}
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check_same(std::string("[1]\0garbage", 11));
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check_same(std::string("[1\0]", 4));
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check_same(std::string("[1, // c\0\n2]", 12));
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check_same(std::string("[1, /* c\0 */ 2]", 15));
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check_same("\xEF\xBB\xBF[1]");
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check_same("\xEF\xBB[1]");
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check_same(" \t\r\n 7 \n");
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for (const char* text :
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{"[1]\r", "[1]\n", "[1]\r\n", "[1,\r2]", "[1,\r\n2]", "7\r", "\"x\"\r", "{\"a\":\r\n1}\r", "[\n 1,\n 2\n]", "{\n \"a\": [\n 1\n ]\n}"
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})
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{
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check_same(text);
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}
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}
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SECTION("deep nesting")
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{
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// the open containers beyond 64 levels live on the heap
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for (const std::size_t depth :
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{
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63u, 64u, 65u, 1000u, 100000u
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})
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{
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const std::string arrays = std::string(depth, '[') + std::string(depth, ']');
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const built b = build(arrays, false, false, false);
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REQUIRE(b.ok);
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CHECK(b.data->tape_size == depth);
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CHECK(b.data->tape[0].next == depth);
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std::string objects;
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for (std::size_t i = 0; i < depth; ++i)
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{
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objects += "{\"a\":";
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}
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objects += '1' + std::string(depth, '}');
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const built o = build(objects, false, false, false);
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REQUIRE(o.ok);
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CHECK(o.data->tape_size == (2 * depth) + 1);
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CHECK(!build(std::string(depth, '[') + std::string(depth - 1, ']'), false, false, false).ok);
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}
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}
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SECTION("generated documents and damaged copies")
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{
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generator g;
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for (int i = 0; i < 3000; ++i)
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{
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std::string text;
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g.value(text, 0);
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check_same(text);
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// damage: flip one byte, or cut the text
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std::string damaged = text;
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const auto at = static_cast<std::size_t>(g.r(static_cast<int>(damaged.size())));
|
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static const char replacements[] = {'x', '"', '\\', ',', ':', ']', '}', '[', '{', '1', '-', '.', 'e', '\0', '\n', '/'}; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
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damaged[at] = replacements[g.r(16)];
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check_same(damaged);
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check_same(text.substr(0, at));
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}
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}
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|
||||
SECTION("test files")
|
||||
{
|
||||
for (const char* name :
|
||||
{
|
||||
"/json.org/1.json", "/json.org/2.json", "/json.org/3.json", "/json.org/4.json", "/json.org/5.json",
|
||||
"/json_testsuite/sample.json", "/nativejson-benchmark/canada.json", "/nativejson-benchmark/citm_catalog.json",
|
||||
"/nativejson-benchmark/twitter.json", "/json_tests/pass1.json", "/json_tests/pass2.json", "/json_tests/pass3.json"
|
||||
})
|
||||
{
|
||||
CAPTURE(name)
|
||||
std::ifstream f(std::string(TEST_DATA_DIRECTORY) + name, std::ios::binary);
|
||||
std::stringstream ss;
|
||||
ss << f.rdbuf();
|
||||
const std::string text = ss.str();
|
||||
REQUIRE(!text.empty());
|
||||
const built b = build(text, false, false, true);
|
||||
REQUIRE(b.ok);
|
||||
CHECK(value_of(b) == json::parse(text));
|
||||
}
|
||||
}
|
||||
}
|
||||
Reference in new issue
Block a user