https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113111
Bug ID: 113111
Summary: -Werror=uninitialized is not consistent for
optimization level 0 or -std=before-c++20
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: MikeSmith32564 at mail dot com
Target Milestone: ---
The following snippet:
#include <string>
#include <iostream>
struct Dummy
{
std::string val;
};
int main()
{
Dummy d =
{
d.val = "random text
#########################################################"
};
std::cout<<d.val<<"\n";
}
when built with:
g++ -std=c++20 -O0 -Wall -Werror main.cpp -o a.out
should generate a warning a.k.a. compilation error due to -Werror about trying
to assign from an uninitialized variable. When -O1, -O2 or -O3 are used the
expected warning is shown:
include/c++/14.0.0/bits/basic_string.h:1084:16: error:
'd.Dummy::val.std::__cxx11::basic_string<char>::_M_string_length' is used
uninitialized [-Werror=uninitialized]
1084 | { return _M_string_length; }
| ^~~~~~~~~~~~~~~~
The example triggers undefined behavior when executed of course due to running
std::string::operator= with the this pointer pointing to uninitialized memory
but I believe a warning should be raised when building regardless of the
optimization level selected.
Strangely, standards before c++20 also do not report the warning.
