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JSON_DIAGNOSTIC_POSITIONS: comparing a value-initialized iterator throws instead of crashing (#6003)

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

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>

* Declare the value-initialized iterator in the test const

clang-tidy (misc-const-correctness) flags it, as it is only compared.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasAgbDGG28MqXjQvLqp
Signed-off-by: Claude <noreply@anthropic.com>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Signed-off-by: Claude <noreply@anthropic.com>
Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Niels LohmannandClaude Opus 5.5 authored and GitHub committed 2026-11-02 17:47:48 +01:00
1 parent 76dbe8f9c9
commit 03d408aafa
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()), ") ");
}