https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104492
Bug ID: 104492
Summary: Bogus dangling pointer warning (dangling pointer to
‘candidates’ may be used [-Werror=dangling-pointer=])
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: thiago at kde dot org
Target Milestone: ---
Created attachment 52409
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52409&action=edit
Preprocessed sources for qlibrary.cpp
Workaround: https://codereview.qt-project.org/c/qt/qtbase/+/394894
Original sources:
https://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/plugin/qlibrary.cpp?id=5e378aaff61c9708e0657f3ee29517c06cb075fa#n618
https://github.com/qt/qtbase/blob/5e378aaff61c9708e0657f3ee29517c06cb075fa/src/corelib/plugin/qlibrary.cpp#L618-L677
Code snippet:
auto isValidSuffix = [](QStringView s) {
const QLatin1String candidates[] = {
QLatin1String("so"),
};
return std::find(std::begin(candidates), std::end(candidates), s) !=
std::end(candidates);
};
auto suffixes = qTokenize(completeSuffix, u'.');
auto it = suffixes.begin();
const auto end = suffixes.end();
while (it != end) {
if (isValidSuffix(*it++))
return true;
}
return false;
This code above produces the warning:
qlibrary.cpp:114:9: error: dangling pointer to ‘candidates’ may be used
[-Werror=dangling-pointer=]
114 | if (isValidSuffix(*it++))
| ^~
qlibrary.cpp:76:29: note: ‘candidates’ declared here
76 | const QLatin1String candidates[] = {
| ^~~~~~~~~~
The 'candidates' variable has indeed gone out of scope, but there's no use of
its pointer where the lambda is used. The lambda does a std::find, which
returns a pointer into the array, but that pointer is compared to std::end and
the lambda returns a boolean.
Compile the attached preprocessed sources with:
g++ -march=x86-64-v3 -Wall -Wextra -O3 -o /dev/null -c qlibrary.cpp.ii
GCC commit 1ce5395977f37e8d0c03394f7b932a584ce85cc7 (master branch dated
2022-02-09).
