vector of structs inline initialization. braced-init-list

问题

I ran into a strange issue which unfortunately, I cannot reproduce outside my application itself. The situation is as below. I have the following struct.

struct Foo {
    std::string first;
    std::string second;
    bool flag;
    float value;
};

One of my classes has a member std::vector<Foo> fooList which undergoes the following set of operations periodically.

void someOperation() {
    UpdateFooList(); //< Updates existing members of fooList
    UseFooList(); //< Do some useful stuff with the new values.
    fooList.clear();

    // Repopulate fooList which is where the problem is. The call below
    // has never worked here. It results in either junk values 
    // in fooList[0] or some of the member values at [0] before the clear() call
    // appear to be retained after the emplace_back
    fooList.emplace_back(Foo{"First", "Second", true, 0.0f}); 
}

Here are the things I have tried.

To make sure there was no data corruption, tried putting in mutexes everywhere there is an access to fooList.
Tried creating a 4 value ctor to Foo with the signature Foo(const std::string&, const std::string&, bool, float) and used this ctor instead of the brace-init-list. No luck here.
Tried replacing emplace_back with push_back in the code above. This did not help either.
Tried reproducing these problems in an isolated cpp file and it works exactly as expected.

The only thing that appears to work in the application is if I replace the emplace_back with the following two lines.

auto fooEntry = Foo{"First", "Second", true, 0.0f};
fooList.push_back(fooEntry); //< This works as expected.
fooList.emplace_back(fooEntry); //< This also works as expected

Any thoughts on why the inline calls of fooList.emplace_back(Foo{"First", "Second", true, 0.0f}); does not work?

I am on gcc-7.2.0 and the application is compiled using c++14 standards.

While this bit of information may not be relevant adding it here for completeness. The class under consideration is compiled using c++14 and exposed via a .so file, while the application itself is compiled using c++17 and loads the .so. The members of the class under consideration are not exposed outside the class. Just the class methods are public.

来源：https://stackoverflow.com/questions/53161886/vector-of-structs-inline-initialization-braced-init-list

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c++

stl