• robinm@programming.dev
    0·
    12 days ago
    void foo() {
    std::vector v = {0, 1, 2, 4};
    const auto& ref = v[1];
    add_missing_values(v);
    std::cout << ref << "\n";
}

void add_missing_values(std::vector<int>& v) {
    // ...
    v.push_back(3);
}

    Neither foo(), nor add_missing_values() looks suspicious. Nonetheless, if v.push_back(3) requires v to grow, then ref becomes an invalid reference and std::cout << ref becomes UB (use after free). In Rust this would not compiles.

    It is order of magnitudes easier to have lifetime errors in C++ than in Rust (use after free, double free, data races, use before initialisation, …)

      • robinm@programming.dev
        0·
        9 days ago

        I think you have a hard time understanding the différence between “not possible” and “much harder”.

        In Rust, the code does not compile.

        In C++ the code compile, but

        • if you have a test case
        • this test case triggers the bug (it is not guarateed to properly reproduce you production environment since it depends on the parameters of the allocator of your vector)
        • you use ubsan

        … then the bug will be caught.

        Yes it is possible, noone says the opposite. But you can’t deny it’s harder. And because its harder, more bugs get past review, most notably security bugs as demonstrated again and again in many studies. The