“ std :: string const& s”和“ std :: string const& s”之间有什么区别？和“ const std :: string& s”？

std :: string const& 是等同于 const std :: string& 。

const std :: string& ; 是Stroustrup的 C ++编程语言中采用的样式，并且可能是传统样式。

const std::string & is the style adopted in Stroustrup's The C++ Programming Language and probably is "the traditional style".

std :: string const& 可能比替代方法更一致：

std::string const & can be more consistent than the alternative:

the const-on-the-right样式始终将 const 置于其所表示的内容的右侧，而另一种样式有时会将 const 在左侧，有时在右侧。

the const-on-the-right style always puts the const on the right of what it constifies, whereas the other style sometimes puts the const on the left and sometimes on the right.

使用const-on-the-right样式，可以用const定义const局部变量。在右边： int const a = 42; 。同样，将const静态变量定义为 static double const x = 3.14; 。基本上，每个 const 都位于它所构成的事物的右侧，包括 const 必须位于正确：具有const成员函数。

With the const-on-the-right style, a local variable that is const is defined with the const on the right: int const a = 42;. Similarly a static variable that is const is defined as static double const x = 3.14;. Basically every const ends up on the right of the thing it constifies, including the const that is required to be on the right: with a const member function.

（请参见 X const& x和 X const * p是什么意思？）。

如果您决定使用const-on-the-right样式，请确保不要误输入 std :: string const& s 作为荒谬的 std :: string& const s ：

If you decide to use const-on-the-right style, make sure to don't mis-type std::string const &s as the nonsensical std::string & const s:

以上声明的意思是： s 是 const 引用 std :: string 。
这是多余的，因为引用始终为 const （您永远都不能重置引用以使其引用其他对象）。

The above declaration means: "s is a const reference to a std::string". It's redundant since references are always const (you can never reset a reference to make it refer to a different object).