https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116742
Bug ID: 116742
Summary: -Wuninitialized failed to issue uninitialized variable
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xiaohuba2021 at 163 dot com
Target Milestone: ---
The following code WON'T generate any warning with -O2 -Wuninitialized
-Wmaybe-uninitialized:
```
#include <iostream>
using namespace std;
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n, s = n; // n is uninitialized
cin >> n;
cout << s << endl;
return 0;
}
```
Turning on -Wall -Wextra does not help.
However, with `ios_base::sync_with_stdio(false)` and `cin.tie(0)` commented,
the compiler will notice that n is uninitialized.
g++ version:
```
Using built-in specs.
COLLECT_GCC=/opt/compiler-explorer/gcc-snapshot/bin/g++
Target: x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.0 20240916 (experimental)
(Compiler-Explorer-Build-gcc-4f2cd256aace732bff511c59f5871456a564a3a5-binutils-2.42)
```
compiler explorer: https://godbolt.org/z/dWbcjq7vn
