Question

我经常听说＆＃34; C ++源代码需要花费大量的时间和内存来编译＃34;

我也听说C ++模板是Turing完成的，所以它可能会受Halting problem的影响。

我还构建了一个C ++项目，需要花费8 GiB的内存和2小时的时间。

所以，问题是：是否存在可以无限时间编译的C ++代码？

（嵌套包含或嵌套模板是可检测的，因此不应计算。）

相关问题：Is there a C++ code that compiles with infinite memory?（我将它们分开，因为我期待不同的答案。）

Answer 1

理论上，这将编译为“无限”。时间因为模板扩展是无限递归的：

template <size_t N>
struct eat
{
    static constexpr size_t value = eat<N+1>::value;
};

但是，我使用的所有编译器都会对这种代码进行防御，发出的错误很像：

/Users/richardh/Documents/dev/Scratchpad/tryit/tryit/words.cpp:136:37: fatal error: recursive template instantiation exceeded maximum depth of 256
    static constexpr size_t value = eat<N+1>::value;
                                    ^
/Users/richardh/Documents/dev/Scratchpad/tryit/tryit/words.cpp:136:37: note: in instantiation of template class 'eat<257>' requested here
    static constexpr size_t value = eat<N+1>::value;
                                    ^
/Users/richardh/Documents/dev/Scratchpad/tryit/tryit/words.cpp:136:37: note: in instantiation of template class 'eat<256>' requested here
    static constexpr size_t value = eat<N+1>::value;
                                    ^
/Users/richardh/Documents/dev/Scratchpad/tryit/tryit/words.cpp:136:37: note: in instantiation of template class 'eat<255>' requested here
    static constexpr size_t value = eat<N+1>::value;
                                    ^
/Users/richardh/Documents/dev/Scratchpad/tryit/tryit/words.cpp:136:37: note: in instantiation of template class 'eat<254>' requested here
    static constexpr size_t value = eat<N+1>::value;

...等

编辑：好吧，我认为这个真的是无限的：

template <class T>
struct eat2
{
    using inner = eat2<eat2<T>>;
    static constexpr int value() {
        return inner::value();
    }
};

int main()
{
    eat2<int> e;
    cout << e.value() << endl;
    return 0;
}

是否有编译无限时间的C ++代码？

1 个答案: