Repository navigation
"May be used uninitialized" warning from g++ 15.2.1 with -O2 #629
Description
First of all, thanks for the library, it is very useful!
I included the library sources (reflectcpp.cpp, reflectcpp_json.cpp and yyjson.c) to my sources and tried building them unoptimized and optimized. Build succeeds without -O flag and with -O1, but some warnings appear with -O2.
Example code (main.cpp):
#include <cstdint>
#include <variant>
#include <vector>
#include <iostream>
#include "rfl/json.hpp"
#include "rfl.hpp"
enum class Enum1 {
Val1, Val2
};
enum class Enum2 {
Val1, Val2
};
enum class Enum3 {
Val1, Val2
};
struct Struct1 {
Enum1 e1;
Enum2 e2;
};
struct Struct2 {
Enum3 e3;
};
using Variant = std::variant<Struct1, Struct2>;
using Vector = std::vector<Variant>;
int main() {
Struct1 s1{Enum1::Val1, Enum2::Val2};
Struct2 s2{Enum3::Val1};
Vector vec{s1, s2};
std::stringstream stream;
rfl::json::write<rfl::AddTagsToVariants>(vec, stream);
const auto res = rfl::json::read<Vector, rfl::AddTagsToVariants>(stream);
if (res) {
rfl::json::write<rfl::AddTagsToVariants>(res.value(), std::cout) << '\n';
} else {
std::cerr << "Failed to read Vector: " << res.error().what() << '\n';
}
}Compiler command:
g++ -Wall -std=c++23 -Werror main.cpp src/reflectcpp.cpp src/reflectcpp_json.cpp src/yyjson.c -I lib/reflect-cpp/include/ -I lib/reflect-cpp/include/rfl/thirdparty/ -O2 >& error.txt
Compiler output is very big, so I'm attaching a separate file: error.txt
reflect-cpp is checked out on tag v0.24.0, g++ version is 15.2.1
Activity
liuzicheng1987 commentedon Mar 8, 2026
@Kirisummer , this does not even appear to be from our library, this piece of code is from the C++ standard library. I also don't know how exactly Object<...>:i_ could be used uninitialized.
liuzicheng1987 commentedon Mar 8, 2026
@Kirisummer , this is very weird, I'll have to take a closer look. Thanks for reporting.
Kirisummer commentedon Mar 8, 2026
The warnings happen on lines with creation of Generic from Array or Null, and Generic is immediately passed to vector::push_back. Some warnings say that is used before initialization. I suspect this might be the case where a temporary value is optimized out.
I will try to create a variable which is then moved inside the vector, or to use emplace_back instead of push_back to avoid creating a temporary value at all.
[Bugfix] Something to do with temporaries