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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>
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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()), ") ");
}