std::nullptr_t

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Defined in header <cstddef>
typedef decltype(nullptr) nullptr_t;
 （C++11 起）
std::nullptr_t是空指针类型的文字，nullptr.
Original:
std::nullptr_t is the type of the null pointer literal, nullptr.
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[编辑] 为例

如果两个或两个以上的重载接受不同的指针类型，过载std::nullptr_t是需要接受一个空指针参数.
Original:
If two or more overloads accept different pointer types, an overload for std::nullptr_t is necessary to accept a null pointer argument.
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#include <cstddef>
#include <iostream>
 
void f(int* pi)
{
   std::cout << "Pointer to integer overload\n";
}
 
void f(double* pd)
{
   std::cout << "Pointer to double overload\n";
}
 
void f(std::nullptr_t nullp)
{
   std::cout << "null pointer overload\n";
}
 
int main()
{
    int* pi; double* pd;
 
    f(pi);
    f(pd);
    f(nullptr);  // would be ambiguous without void f(nullptr_t)
    // f(NULL);  // ambiguous overload: all three functions are candidates
}

Output: 

Pointer to integer overload
Pointer to double overload
null pointer overload

[编辑] 另请参阅

nullptr
指针常量，它指定一个空指针（C++11）
Original:
the pointer literal which specifies a null pointer value （C++11）
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[edit]
实现定义的空指针常量
Original:
implementation-defined null pointer constant
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（宏不变） [edit]
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/types/nullptr_t&oldid=27213”