c++ - 字符串文字的模板参数推导

Question

template<typename T>
void print_size(const T& x)
{
    std::cout << sizeof(x) << '\n';
}

int main()
{
    print_size("If you timidly approach C++ as just a better C or as an object-oriented language, you are going to miss the point.");
    // prints 115
}

这在最近的 g++ 编译器上打印 115。显然，T 被推导为数组(而不是指针)。标准是否保证了这种行为？我有点惊讶，因为下面的代码打印了指针的大小，我认为 auto 的行为与模板参数推导完全一样？

int main()
{
    auto x = "If you timidly approach C++ as just a better C or as an object-oriented language, you are going to miss the point.";
    print_size(x);
    // prints 4
}

Answer 1

auto 的行为与模板参数推导完全相同¹。完全像 T!

比较这个:

template<typename T>
void print_size(T x)
{
    std::cout << sizeof(x) << '\n';
}

int main()
{
    print_size("If you timidly approach C++ as just a better C or as an object-oriented language, you are going to miss the point.");
    // prints 4
    auto x = "If you timidly approach C++ as just a better C or as an object-oriented language, you are going to miss the point.";
    print_size(x);
    // prints 4
}

有了这个:

template<typename T>
void print_size(const T& x)
{
    std::cout << sizeof(x) << '\n';
}

int main()
{
    print_size("If you timidly approach C++ as just a better C or as an object-oriented language, you are going to miss the point.");
    // prints 115
    const auto& x = "If you timidly approach C++ as just a better C or as an object-oriented language, you are going to miss the point.";
    print_size(x);
    // prints 115
}

---

¹ 不完全是，但这不是极端情况之一。