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Use only documented StringType members in json_pointer (#5692)

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contains(const json_pointer&) and operator/=(std::size_t) (and hence
operator/(std::size_t)) used string_t operations that the StringType
template parameter documentation explicitly does not require:
comparing string_t with a const char* literal, c_str(), and
constructibility from std::string. This made both functions fail to
compile for a conforming custom StringType, even though the
documentation's own reference StringType satisfies the requirements.

Fix contains() to compare individual chars ('0'..'9') instead of
comparing string_t with const char* literals, and to call data()
(documented to be null-terminated) instead of c_str(). Fix
operator/=(std::size_t) to build the array-index token via the
existing detail::to_string<StringType> helper (ADL int_to_string() or
assignment from std::to_string()) instead of via std::to_string()
directly, matching how diff(), items(), and std::hash already convert
a std::size_t to a StringType.

Add regression tests to tests/src/unit-alt-string.cpp: contains() for
present/missing keys and indices, "-", a leading zero, and a
non-numeric token on an array, plus json_pointer::operator/(std::size_t).

Fixes #5666.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-30 20:13:31 +02:00
committed by GitHub
parent 6fc0d501f3
commit fdcc569eee
4 changed files with 45 additions and 6 deletions
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include/nlohmann/detail/json_pointer.hpp
+4 -3
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@@ -26,6 +26,7 @@
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/string_concat.hpp>
#include <nlohmann/detail/string_escape.hpp>
#include <nlohmann/detail/string_utils.hpp>
#include <nlohmann/detail/value_t.hpp>
NLOHMANN_JSON_NAMESPACE_BEGIN
@@ -116,7 +117,7 @@ class json_pointer
/// @sa https://json.nlohmann.me/api/json_pointer/operator_slasheq/
json_pointer& operator/=(std::size_t array_idx)
{
return *this /= std::to_string(array_idx);
return *this /= detail::to_string<string_t>(array_idx);
}
/// @brief create a new JSON pointer by appending the right JSON pointer at the end of the left JSON pointer
@@ -752,7 +753,7 @@ class json_pointer
// would throw out_of_range.404 -- contains() must not throw (see #5395)
return false;
}
if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !("0" <= reference_token && reference_token <= "9")))
if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !('0' <= reference_token[0] && reference_token[0] <= '9')))
{
// invalid char
return false;
@@ -780,7 +781,7 @@ class json_pointer
// not throw (see #5395), so such a reference token is treated as "not found"
errno = 0; // strtoull() does not reset errno on success
char* p_end = nullptr; // NOLINT(misc-const-correctness)
const unsigned long long magnitude = std::strtoull(reference_token.c_str(), &p_end, 10); // NOLINT(runtime/int)
const unsigned long long magnitude = std::strtoull(reference_token.data(), &p_end, 10); // NOLINT(runtime/int)
if (JSON_HEDLEY_UNLIKELY(errno == ERANGE // the value exceeds ULLONG_MAX
|| magnitude >= static_cast<unsigned long long>((std::numeric_limits<typename BasicJsonType::size_type>::max)()))) // NOLINT(runtime/int)
{