Files
json/include/nlohmann/detail/conversions/to_json.hpp
T
Niels Lohmann 556027f109 Avoid MSVC 2015's C4800 for enums with underlying type bool
MSVC 2015 warns about any conversion to bool (C4800), even with an
explicit cast, so the enum conversions from #5754 (#5671) failed the
AppVeyor build with /WX. Convert to bool by comparing with zero via the
new detail::bool_aware_static_cast, and keep doctest from printing the
enum in the test.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-05 13:29:32 +02:00

594 lines
22 KiB
C++

// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
#pragma once
#include <nlohmann/detail/macro_scope.hpp> // JSON_HAS_CPP_17
#ifdef JSON_HAS_CPP_17
#include <optional> // optional
#endif
#include <algorithm> // copy
#include <iterator> // begin, end
#include <memory> // allocator_traits
#include <string> // basic_string, char_traits
#include <tuple> // tuple, get
#include <type_traits> // is_same, is_constructible, is_floating_point, is_enum, underlying_type
#include <utility> // move, forward, declval, pair
#include <valarray> // valarray
#include <vector> // vector
#include <nlohmann/detail/exceptions.hpp>
#include <nlohmann/detail/iterators/iteration_proxy.hpp>
#include <nlohmann/detail/meta/cpp_future.hpp>
#include <nlohmann/detail/meta/std_fs.hpp>
#include <nlohmann/detail/meta/type_traits.hpp>
#include <nlohmann/detail/value_t.hpp>
NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{
//////////////////
// constructors //
//////////////////
/*
* Note all external_constructor<>::construct functions need to call
* j.m_data.m_value.destroy(j.m_data.m_type) to avoid a memory leak in case j contains an
* allocated value (e.g., a string). See bug issue
* https://github.com/nlohmann/json/issues/2865 for more information.
*/
template<value_t> struct external_constructor;
template<>
struct external_constructor<value_t::boolean>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::boolean_t b) noexcept
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::boolean;
j.m_data.m_value = b;
j.assert_invariant();
}
};
template<>
struct external_constructor<value_t::string>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::string_t& s)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::string;
j.m_data.m_value = s;
j.assert_invariant();
}
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::string_t&& s)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::string;
j.m_data.m_value = std::move(s);
j.assert_invariant();
}
template < typename BasicJsonType, typename CompatibleStringType,
enable_if_t < !std::is_same<CompatibleStringType, typename BasicJsonType::string_t>::value,
int > = 0 >
static void construct(BasicJsonType& j, const CompatibleStringType& str)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::string;
j.m_data.m_value.string = j.template create<typename BasicJsonType::string_t>(str);
j.assert_invariant();
}
};
template<>
struct external_constructor<value_t::binary>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::binary_t& b)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::binary;
j.m_data.m_value = typename BasicJsonType::binary_t(b);
j.assert_invariant();
}
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::binary_t&& b)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::binary;
j.m_data.m_value = typename BasicJsonType::binary_t(std::move(b));
j.assert_invariant();
}
};
template<>
struct external_constructor<value_t::number_float>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::number_float_t val) noexcept
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::number_float;
j.m_data.m_value = val;
j.assert_invariant();
}
};
template<>
struct external_constructor<value_t::number_unsigned>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::number_unsigned_t val) noexcept
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::number_unsigned;
j.m_data.m_value = val;
j.assert_invariant();
}
};
template<>
struct external_constructor<value_t::number_integer>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::number_integer_t val) noexcept
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::number_integer;
j.m_data.m_value = val;
j.assert_invariant();
}
};
template<>
struct external_constructor<value_t::array>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::array_t& arr)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::array;
j.m_data.m_value = arr;
j.set_parents();
j.assert_invariant();
}
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::array;
j.m_data.m_value = std::move(arr);
j.set_parents();
j.assert_invariant();
}
template < typename BasicJsonType, typename CompatibleArrayType,
enable_if_t < !std::is_same<CompatibleArrayType, typename BasicJsonType::array_t>::value
#if JSON_HAS_RANGE_VIEW_CONVERSION
&& !is_compatible_range_view<CompatibleArrayType>::value
#endif
, int > = 0 >
static void construct(BasicJsonType& j, const CompatibleArrayType& arr)
{
using std::begin;
using std::end;
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::array;
j.m_data.m_value.array = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
j.set_parents();
j.assert_invariant();
}
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const std::vector<bool>& arr)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::array;
j.m_data.m_value = value_t::array;
j.m_data.m_value.array->reserve(arr.size());
for (const bool x : arr)
{
j.m_data.m_value.array->push_back(x);
j.set_parent(j.m_data.m_value.array->back());
}
j.assert_invariant();
}
template<typename BasicJsonType, typename T,
enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
static void construct(BasicJsonType& j, const std::valarray<T>& arr)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::array;
j.m_data.m_value = value_t::array;
j.m_data.m_value.array->resize(arr.size());
std::copy(std::begin(arr), std::end(arr), j.m_data.m_value.array->begin());
j.set_parents();
j.assert_invariant();
}
#if JSON_HAS_RANGE_VIEW_CONVERSION
template<typename BasicJsonType, typename CompatibleArrayType,
enable_if_t<is_compatible_range_view<std::remove_cvref_t<CompatibleArrayType>>::value, int> = 0>
static void construct(BasicJsonType& j, CompatibleArrayType && arr)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::array;
j.m_data.m_value = value_t::array;
for (auto&& x : std::forward<CompatibleArrayType>(arr))
{
j.m_data.m_value.array->push_back(x);
}
// set the parents only once all elements are in place: a push_back
// that reallocates moves the earlier elements, which does not keep
// their parent pointers
j.set_parents();
j.assert_invariant();
}
#endif
};
template<>
struct external_constructor<value_t::object>
{
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::object_t& obj)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::object;
j.m_data.m_value = obj;
j.set_parents();
j.assert_invariant();
}
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
{
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::object;
j.m_data.m_value = std::move(obj);
j.set_parents();
j.assert_invariant();
}
template < typename BasicJsonType, typename CompatibleObjectType,
enable_if_t < !std::is_same<CompatibleObjectType, typename BasicJsonType::object_t>::value, int > = 0 >
static void construct(BasicJsonType& j, const CompatibleObjectType& obj)
{
using std::begin;
using std::end;
j.m_data.m_value.destroy(j.m_data.m_type);
j.m_data.m_type = value_t::object;
j.m_data.m_value.object = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
j.set_parents();
j.assert_invariant();
}
};
/////////////
// to_json //
/////////////
#ifdef JSON_HAS_CPP_17
template<typename BasicJsonType, typename T,
enable_if_t<std::is_constructible<BasicJsonType, T>::value, int> = 0>
void to_json(BasicJsonType& j, const std::optional<T>& opt) noexcept(std::is_nothrow_assignable<BasicJsonType&, const T&>::value)
{
if (opt.has_value())
{
// explicit construction, as the conversion from a basic_json with a different
// string type is explicit if JSON_USE_IMPLICIT_CONVERSIONS is 0 (#2649)
j = BasicJsonType(*opt);
}
else
{
j = nullptr;
}
}
#endif
template<typename BasicJsonType, typename T,
enable_if_t<std::is_same<T, typename BasicJsonType::boolean_t>::value, int> = 0>
inline void to_json(BasicJsonType& j, T b) noexcept
{
external_constructor<value_t::boolean>::construct(j, b);
}
template < typename BasicJsonType, typename BoolRef,
enable_if_t <
((std::is_same<std::vector<bool>::reference, BoolRef>::value
&& !std::is_same <std::vector<bool>::reference, typename BasicJsonType::boolean_t&>::value)
|| (std::is_same<std::vector<bool>::const_reference, BoolRef>::value
&& !std::is_same <detail::uncvref_t<std::vector<bool>::const_reference>,
typename BasicJsonType::boolean_t >::value))
&& std::is_convertible<const BoolRef&, typename BasicJsonType::boolean_t>::value, int > = 0 >
inline void to_json(BasicJsonType& j, const BoolRef& b) noexcept
{
external_constructor<value_t::boolean>::construct(j, static_cast<typename BasicJsonType::boolean_t>(b));
}
template<typename BasicJsonType, typename CompatibleString,
enable_if_t<std::is_constructible<typename BasicJsonType::string_t, CompatibleString>::value, int> = 0>
inline void to_json(BasicJsonType& j, const CompatibleString& s)
{
external_constructor<value_t::string>::construct(j, s);
}
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, typename BasicJsonType::string_t&& s)
{
external_constructor<value_t::string>::construct(j, std::move(s));
}
template<typename BasicJsonType, typename FloatType,
enable_if_t<std::is_floating_point<FloatType>::value, int> = 0>
inline void to_json(BasicJsonType& j, FloatType val) noexcept
{
external_constructor<value_t::number_float>::construct(j, static_cast<typename BasicJsonType::number_float_t>(val));
}
template<typename BasicJsonType, typename CompatibleNumberUnsignedType,
enable_if_t<is_compatible_integer_type<typename BasicJsonType::number_unsigned_t, CompatibleNumberUnsignedType>::value, int> = 0>
inline void to_json(BasicJsonType& j, CompatibleNumberUnsignedType val) noexcept
{
external_constructor<value_t::number_unsigned>::construct(j, static_cast<typename BasicJsonType::number_unsigned_t>(val));
}
template<typename BasicJsonType, typename CompatibleNumberIntegerType,
enable_if_t<is_compatible_integer_type<typename BasicJsonType::number_integer_t, CompatibleNumberIntegerType>::value, int> = 0>
inline void to_json(BasicJsonType& j, CompatibleNumberIntegerType val) noexcept
{
external_constructor<value_t::number_integer>::construct(j, static_cast<typename BasicJsonType::number_integer_t>(val));
}
#if !JSON_DISABLE_ENUM_SERIALIZATION
template<typename BasicJsonType, typename EnumType,
enable_if_t<std::is_enum<EnumType>::value, int> = 0>
inline void to_json(BasicJsonType& j, EnumType e) noexcept
{
using underlying_type = typename std::underlying_type<EnumType>::type;
static constexpr value_t integral_value_t = std::is_unsigned<underlying_type>::value ? value_t::number_unsigned : value_t::number_integer;
external_constructor<integral_value_t>::construct(j, bool_aware_static_cast<underlying_type>(e));
}
#endif // JSON_DISABLE_ENUM_SERIALIZATION
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const std::vector<bool>& e)
{
external_constructor<value_t::array>::construct(j, e);
}
template < typename BasicJsonType, typename CompatibleArrayType,
enable_if_t < is_compatible_array_type<BasicJsonType,
CompatibleArrayType>::value&&
!is_compatible_object_type<BasicJsonType, CompatibleArrayType>::value&&
!is_compatible_string_type<BasicJsonType, CompatibleArrayType>::value&&
!std::is_same<typename BasicJsonType::binary_t, CompatibleArrayType>::value&&
!is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value&&
!is_basic_json<CompatibleArrayType>::value
#if JSON_HAS_RANGE_VIEW_CONVERSION
&& !is_compatible_range_view<CompatibleArrayType>::value
#endif
#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
&& !is_enum_keyed_map<CompatibleArrayType>::value
#endif
,
int > = 0 >
inline void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
{
external_constructor<value_t::array>::construct(j, arr);
}
#if JSON_HAS_RANGE_VIEW_CONVERSION
template < typename BasicJsonType, typename T,
enable_if_t < is_compatible_range_view<std::remove_cvref_t<T>>::value
&& !is_compatible_string_type<BasicJsonType, std::remove_cvref_t<T>>::value
&& !is_compatible_object_type<BasicJsonType, std::remove_cvref_t<T>>::value
&& !is_basic_json<std::remove_cvref_t<T>>::value, int > = 0 >
inline void to_json(BasicJsonType& j, T && arr)
{
external_constructor<value_t::array>::construct(j, std::forward<T>(arr));
}
#endif
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const typename BasicJsonType::binary_t& bin)
{
external_constructor<value_t::binary>::construct(j, bin);
}
template < typename BasicJsonType, typename CompatibleArrayType,
enable_if_t < is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value,
int > = 0 >
inline void to_json(BasicJsonType& j, const CompatibleArrayType& bin)
{
external_constructor<value_t::binary>::construct(j, typename BasicJsonType::binary_t(bin));
}
template<typename BasicJsonType, typename T,
enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
inline void to_json(BasicJsonType& j, const std::valarray<T>& arr)
{
external_constructor<value_t::array>::construct(j, std::move(arr));
}
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
{
external_constructor<value_t::array>::construct(j, std::move(arr));
}
template < typename BasicJsonType, typename CompatibleObjectType,
enable_if_t < is_compatible_object_type<BasicJsonType, CompatibleObjectType>::value&& !is_basic_json<CompatibleObjectType>::value, int > = 0 >
inline void to_json(BasicJsonType& j, const CompatibleObjectType& obj)
{
external_constructor<value_t::object>::construct(j, obj);
}
#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
// store a map with enum keys as an object, using the enum's own to_json for the
// keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); without the macro, such maps
// are stored as arrays of [key, value] pairs
template < typename BasicJsonType, typename EnumKeyedMap,
enable_if_t < is_enum_keyed_map<EnumKeyedMap>::value&& !is_basic_json<EnumKeyedMap>::value, int > = 0 >
inline void to_json(BasicJsonType& j, const EnumKeyedMap& map)
{
typename BasicJsonType::object_t obj;
for (const auto& p : map)
{
BasicJsonType key = p.first;
if (JSON_HEDLEY_UNLIKELY(!key.is_string()))
{
JSON_THROW(type_error::create(302, concat("type must be string, but is ", key.type_name()), &key));
}
auto& key_string = *key.template get_ptr<typename BasicJsonType::string_t*>();
if (JSON_HEDLEY_UNLIKELY(!obj.emplace(key_string, BasicJsonType(p.second)).second))
{
JSON_THROW(type_error::create(318, concat("duplicate object key '", key_string, "'"), &key));
}
}
external_constructor<value_t::object>::construct(j, std::move(obj));
}
#endif
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
{
external_constructor<value_t::object>::construct(j, std::move(obj));
}
template <
typename BasicJsonType, typename T, std::size_t N,
enable_if_t < !std::is_constructible<typename BasicJsonType::string_t,
const T(&)[N]>::value, // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
int > = 0 >
inline void to_json(BasicJsonType& j, const T(&arr)[N]) // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
{
external_constructor<value_t::array>::construct(j, arr);
}
template < typename BasicJsonType, typename T1, typename T2, enable_if_t < std::is_constructible<BasicJsonType, T1>::value&& std::is_constructible<BasicJsonType, T2>::value, int > = 0 >
inline void to_json(BasicJsonType& j, const std::pair<T1, T2>& p)
{
j = { p.first, p.second };
}
// for https://github.com/nlohmann/json/pull/1134
template<typename BasicJsonType, typename T,
enable_if_t<std::is_same<T, iteration_proxy_value<typename BasicJsonType::iterator>>::value, int> = 0>
inline void to_json(BasicJsonType& j, const T& b)
{
j = { {b.key(), b.value()} };
}
template<typename BasicJsonType, typename Tuple, std::size_t... Idx>
inline void to_json_tuple_impl(BasicJsonType& j, const Tuple& t, index_sequence<Idx...> /*unused*/)
{
j = { std::get<Idx>(t)... };
}
// A one-element braced list does not reliably wrap its element: with
// JSON_BRACE_INIT_COPY_SEMANTICS it copies it, which would serialize
// std::tuple<int>{5} as 5 rather than [5], and some compilers (e.g., Apple clang
// 15 and 16) copy an element that is itself a basic_json even without it, so
// std::tuple<json>{true} became true rather than [true]. Build what the default
// deduction builds instead: an object if the element is a [string, value] pair,
// a one-element array otherwise.
template<typename BasicJsonType, typename Tuple>
inline void to_json_tuple_impl(BasicJsonType& j, const Tuple& t, index_sequence<0> /*unused*/)
{
BasicJsonType element(std::get<0>(t));
// same test as the initializer-list constructor, including the cast that
// keeps a string type constructible from 0 from selecting operator[](key)
const bool is_member = element.is_array() && element.size() == 2
&& element[static_cast<typename BasicJsonType::size_type>(0)].is_string();
if (is_member)
{
j = BasicJsonType::object({std::move(element)});
}
else
{
j = BasicJsonType::array({std::move(element)});
}
}
template<typename BasicJsonType, typename Tuple>
inline void to_json_tuple_impl(BasicJsonType& j, const Tuple& /*unused*/, index_sequence<> /*unused*/)
{
using array_t = typename BasicJsonType::array_t;
j = array_t();
}
template<typename BasicJsonType, typename T, enable_if_t<is_constructible_tuple<BasicJsonType, T>::value, int > = 0>
inline void to_json(BasicJsonType& j, const T& t)
{
to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
}
#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
#if defined(__cpp_lib_char8_t)
template<typename BasicJsonType, typename Tr, typename Allocator>
inline void to_json(BasicJsonType& j, const std::basic_string<char8_t, Tr, Allocator>& s)
{
using OtherAllocator = typename std::allocator_traits<Allocator>::template rebind_alloc<char>;
j = std::basic_string<char, std::char_traits<char>, OtherAllocator>(s.begin(), s.end(), s.get_allocator());
}
#endif
// Workaround for MSVC 19.51 (and possibly later): in large cpp files, the compiler may fail to resolve with generic has_to_json (issue #4996)
template<typename BasicJsonType>
struct has_to_json<BasicJsonType, std_fs::path, void> : std::true_type {};
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const std_fs::path& p)
{
// Returns either a std::string or a std::u8string depending whether library
// support for char8_t is enabled.
j = p.u8string();
}
#endif
struct to_json_fn
{
template<typename BasicJsonType, typename T>
auto operator()(BasicJsonType& j, T&& val) const noexcept(noexcept(to_json(j, std::forward<T>(val))))
-> decltype(to_json(j, std::forward<T>(val)), void())
{
return to_json(j, std::forward<T>(val));
}
};
} // namespace detail
#ifndef JSON_HAS_CPP_17
/// namespace to hold default `to_json` function
/// to see why this is required:
/// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4381.html
namespace // NOLINT(cert-dcl59-cpp,fuchsia-header-anon-namespaces,google-build-namespaces,misc-anonymous-namespace-in-header)
{
#endif
JSON_INLINE_VARIABLE constexpr const auto& to_json = // NOLINT(misc-definitions-in-headers)
detail::static_const<detail::to_json_fn>::value;
#ifndef JSON_HAS_CPP_17
} // namespace
#endif
NLOHMANN_JSON_NAMESPACE_END