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Create a value before giving it its type

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Squashed onto develop from:
- Create a value before giving it its type
- Skip the failed-allocation test when exceptions are disabled
- Keep the created pointer rather than an uninitialized json_value
- Skip the vector<bool> failed-allocation check for VS 2015 with iterator debugging
- Test the remaining to_json overloads with a failing allocation
- Skip the to_json allocation-failure section on VS 2015 Debug
- Fix false GCC -Warray-bounds error with JSON_DIAGNOSTICS at -O3 (#5744)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-06 07:26:53 +02:00
1 parent 8a142bc436
commit 6887cf7e53
6 files changed
+360 -60
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include/nlohmann/detail/conversions/to_json.hpp
+44 -24
View File
@@ -43,6 +43,10 @@ namespace detail
* 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.
*
* A value that has to be allocated is created before the old one is destroyed:
* were it the other way around, an exception while creating the new value would
* leave j with the type of the new value, but the pointer to the destroyed old one.
*/
template<value_t> struct external_constructor;
@@ -66,18 +70,20 @@ struct external_constructor<value_t::string>
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::string_t& s)
{
const typename BasicJsonType::json_value value(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.m_data.m_value = value;
j.assert_invariant();
}
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::string_t&& s)
{
const typename BasicJsonType::json_value value(std::move(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.m_data.m_value = value;
j.assert_invariant();
}
@@ -86,9 +92,10 @@ struct external_constructor<value_t::string>
int > = 0 >
static void construct(BasicJsonType& j, const CompatibleStringType& str)
{
auto* created = j.template create<typename BasicJsonType::string_t>(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.m_data.m_value.string = created;
j.assert_invariant();
}
};
@@ -99,18 +106,20 @@ struct external_constructor<value_t::binary>
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::binary_t& b)
{
const typename BasicJsonType::json_value value(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.m_data.m_value = value;
j.assert_invariant();
}
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::binary_t&& b)
{
const typename BasicJsonType::json_value value(std::move(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.m_data.m_value = value;
j.assert_invariant();
}
};
@@ -160,9 +169,10 @@ struct external_constructor<value_t::array>
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::array_t& arr)
{
const typename BasicJsonType::json_value value(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.m_data.m_value = value;
j.set_parents();
j.assert_invariant();
}
@@ -170,9 +180,10 @@ struct external_constructor<value_t::array>
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
{
const typename BasicJsonType::json_value value(std::move(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.m_data.m_value = value;
j.set_parents();
j.assert_invariant();
}
@@ -188,9 +199,10 @@ struct external_constructor<value_t::array>
using std::begin;
using std::end;
auto* created = j.template create<typename BasicJsonType::array_t>(begin(arr), end(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.array = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
j.m_data.m_value.array = created;
j.set_parents();
j.assert_invariant();
}
@@ -198,15 +210,17 @@ struct external_constructor<value_t::array>
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());
typename BasicJsonType::array_t elements;
elements.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());
elements.push_back(x);
}
const typename BasicJsonType::json_value value(std::move(elements));
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;
j.set_parents();
j.assert_invariant();
}
@@ -214,11 +228,12 @@ struct external_constructor<value_t::array>
enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
static void construct(BasicJsonType& j, const std::valarray<T>& arr)
{
typename BasicJsonType::array_t elements(arr.size());
std::copy(std::begin(arr), std::end(arr), elements.begin());
const typename BasicJsonType::json_value value(std::move(elements));
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.m_data.m_value = value;
j.set_parents();
j.assert_invariant();
}
@@ -228,13 +243,15 @@ struct external_constructor<value_t::array>
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;
typename BasicJsonType::array_t elements;
for (auto&& x : std::forward<CompatibleArrayType>(arr))
{
j.m_data.m_value.array->push_back(x);
elements.push_back(x);
}
const typename BasicJsonType::json_value value(std::move(elements));
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;
// 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
@@ -250,9 +267,10 @@ struct external_constructor<value_t::object>
template<typename BasicJsonType>
static void construct(BasicJsonType& j, const typename BasicJsonType::object_t& obj)
{
const typename BasicJsonType::json_value value(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.m_data.m_value = value;
j.set_parents();
j.assert_invariant();
}
@@ -260,9 +278,10 @@ struct external_constructor<value_t::object>
template<typename BasicJsonType>
static void construct(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
{
const typename BasicJsonType::json_value value(std::move(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.m_data.m_value = value;
j.set_parents();
j.assert_invariant();
}
@@ -274,9 +293,10 @@ struct external_constructor<value_t::object>
using std::begin;
using std::end;
auto* created = j.template create<typename BasicJsonType::object_t>(begin(obj), end(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.object = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
j.m_data.m_value.object = created;
j.set_parents();
j.assert_invariant();
}
include/nlohmann/json.hpp
+6 -6
View File
@@ -2056,8 +2056,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
if (is_an_object)
{
// the initializer list is a list of pairs -> create an object
m_data.m_type = value_t::object;
m_data.m_value = value_t::object;
m_data.m_type = value_t::object;
for (auto& element_ref : init)
{
@@ -2079,8 +2079,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
}
#endif
// the initializer list describes an array -> create an array
m_data.m_type = value_t::array;
m_data.m_value.array = create<array_t>(init.begin(), init.end());
m_data.m_type = value_t::array;
}
set_parents();
@@ -2093,8 +2093,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
static basic_json binary(const typename binary_t::container_type& init)
{
auto res = basic_json();
res.m_data.m_type = value_t::binary;
res.m_data.m_value = init;
res.m_data.m_type = value_t::binary;
return res;
}
@@ -2104,8 +2104,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
static basic_json binary(const typename binary_t::container_type& init, typename binary_t::subtype_type subtype)
{
auto res = basic_json();
res.m_data.m_type = value_t::binary;
res.m_data.m_value = binary_t(init, subtype);
res.m_data.m_type = value_t::binary;
return res;
}
@@ -2115,8 +2115,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
static basic_json binary(typename binary_t::container_type&& init)
{
auto res = basic_json();
res.m_data.m_type = value_t::binary;
res.m_data.m_value = std::move(init);
res.m_data.m_type = value_t::binary;
return res;
}
@@ -2126,8 +2126,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
static basic_json binary(typename binary_t::container_type&& init, typename binary_t::subtype_type subtype)
{
auto res = basic_json();
res.m_data.m_type = value_t::binary;
res.m_data.m_value = binary_t(std::move(init), subtype);
res.m_data.m_type = value_t::binary;
return res;
}