使用 nullptr 有什么好处?
这段代码概念上对三个指针做了同样的事情(安全指针初始化):
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;
那么，分配指针 nullptr 与分配值 NULL 或 0 相比有什么优势?
And so, what are the advantages of assigning pointers nullptr over assigning them the values NULL or 0?
推荐答案
在那段代码中，似乎没有什么优势.但请考虑以下重载函数:
In that code, there doesn't seem to be an advantage. But consider the following overloaded functions:
void f(char const *ptr);
void f(int v);
f(NULL); //which function will be called?
会调用哪个函数?当然，这里的意图是调用f(char const *)，但实际上会调用f(int)！这是个大问题1，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 problem1, isn't it?
所以，解决此类问题的方法是使用nullptr:
So, the solution to such problems is to use nullptr:
f(nullptr); //first function is called
<小时>
当然，这不是 nullptr 的唯一优势.这是另一个:
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的类型被推导出为nullptr_t，所以你可以这样写:
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!!!
<小时>
1.在C++中，NULL被定义为#define NULL 0，所以基本上是int，这就是为什么f(int) 被调用.
1. In C++, NULL is defined as #define NULL 0, so it is basically int, that is why f(int) is called.
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