问题描述
这段代码在概念上对三个指针（安全指针初始化）有同样的作用：
This piece of code conceptually does the same thing for the three pointers (safe pointer initialization):
int* p1 = nullptr;
int* p2 = NULL;
int* p3 = 0;
因此，赋值指针的优点是 nullptr over给它们赋值 NULL 或 0 ？
And so, what are the advantages of assigning pointers nullptr over assigning them the values NULL or 0?
推荐答案
在该代码中，似乎没有优势。但是请看这些重载函数：
In that code, there doesn't seem to be an advantage. But see these overloaded functions:
void f(char const *ptr);
void f(int v);
f(NULL); //which function will be called?
将调用哪个函数？当然，这里的意图是调用 f（char const *），但实际上 f（int）叫做！！这是一个大问题，不是吗？
Which function will be called? Of course, the intention here is to call f(char const *), but in reality f(int) will be called!! That is a big problem, isn't it?
所以，解决这样的问题是使用 nullptr ：
So, the solution to such problems is to use nullptr:
f(nullptr); //first function is called
当然，不是 nullptr 的唯一优势。这里是另一个：
Of course, that is not the only advantage of nullptr. Here is another:
template<typename T, T *ptr>
struct something{}; //primary template
template<>
struct something<nullptr_t, nullptr>{}; //partial specialization for nullptr
由于在模板中， nullptr 被推导为 nullptr_t ，因此您可以写成：
Since in template, the type of nullptr is deduced as nullptr_t, so you can write this:
template<typename T>
void f(T *ptr); //function to handle non-nullptr argument
void f(nullptr_t); //an overload to handle nullptr argument!!!
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