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JSON_DIAGNOSTIC_POSITIONS: comparing a value-initialized iterator throws instead of crashing

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With JSON_DIAGNOSTIC_POSITIONS, comparing a value-initialized iterator
(which has no container) with another iterator built the
invalid_iterator.212 message from the byte positions of the iterator's
value, which is a null pointer: UBSan reports "member call on null
pointer" in exception::get_byte_positions(), then the process crashes.
Every other configuration throws invalid_iterator.212.

get_byte_positions() now returns no positions for a null value, as the
JSON_DIAGNOSTICS path already does.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-11-02 06:58:15 +01:00
1 parent b2674a4a2f
commit 0eabcc51eb
3 files changed
+15 -2
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include/nlohmann/detail/exceptions.hpp
+2 -1
View File
@@ -222,7 +222,8 @@ class exception : public std::exception
template<typename BasicJsonType>
static std::string get_byte_positions(const BasicJsonType* leaf_element)
{
if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
// a value-initialized iterator has no value (invalid_iterator.212)
if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
{
return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
}
single_include/nlohmann/json.hpp
Generated
+2 -1
View File
@@ -5719,7 +5719,8 @@ class exception : public std::exception
template<typename BasicJsonType>
static std::string get_byte_positions(const BasicJsonType* leaf_element)
{
if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
// a value-initialized iterator has no value (invalid_iterator.212)
if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
{
return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
}
tests/src/unit-diagnostic-positions.cpp
+11
View File
@@ -243,3 +243,14 @@ TEST_CASE("values read from a binary format have no positions")
check_no_positions(j);
}
}
TEST_CASE("comparing a value-initialized iterator throws invalid_iterator.212")
{
// such an iterator has no value to take the byte positions from; the
// comparison used to dereference the null pointer instead of throwing
json j = {1, 2};
json::iterator it{};
CHECK_THROWS_WITH_AS(it == j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
CHECK_THROWS_WITH_AS(it < j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
CHECK_THROWS_WITH_AS(j.begin() == it, "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
}