Why did MSVC emit the C24695 warning?

[Mq-b]

I was using the MSVC toolchain and CMake on windows when I got a C26495 warning telling me that m_data was uninitialized.

https://github.com/nlohmann/json/blob/620034e/include/nlohmann/json.hpp#L1142

Testing other compilers does not have this problem.

code:

#include <iostream>
#include <string>
#include <vector>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

struct Person {
    std::string name;
    int age;
    std::vector<std::string> hobbies;

    friend void to_json(json& j, const Person& p) {
        j = json{{"name", p.name}, {"age", p.age}, {"hobbies", p.hobbies}};
    }

    friend void from_json(const json& j, Person& p) {
        j.at("name").get_to(p.name);
        j.at("age").get_to(p.age);
        j.at("hobbies").get_to(p.hobbies);
    }
};

int main() {
    Person person = {"John Doe", 30, {"Reading", "Traveling", "Swimming"}};

    json j = person;
    std::cout << "Serialized JSON:\n" << j.dump(4) << std::endl;

    std::string serialized_json = j.dump();

    json j2 = json::parse(serialized_json);
    Person new_person = j2.get<Person>();

    std::cout << "Deserialized Person:\n"
              << "Name: " << new_person.name << "\n"
              << "Age: " << new_person.age << "\n"
              << "Hobbies: ";
    for (const auto& hobby : new_person.hobbies) {
        std::cout << hobby << " ";
    }
    std::cout << std::endl;
}

https://godbolt.org/z/WTb78WvaW

CMakeList.txt:

find_package(nlohmann_json 3.2.0 REQUIRED)
target_link_libraries(${PROJECT_NAME} PRIVATE nlohmann_json::nlohmann_json)

Image:

[Mq-b]

But I looked at the definition and it was initialized. Is this a BUG in MSVC?

    data m_data = {};

https://github.com/nlohmann/json/blob/620034e/include/nlohmann/json.hpp#L4221

[frederick-vs-ja]

This is actually a bug of MSVC. Reduced and reported DevCom-10815325.

[Mq-b]

Thanks