C++11---nullptr

"1" About 0 and NULL

"2" on the nullptr and void* of the law

Nullptr habits are called pointer null values

Void* habits are called untyped pointers

"3" nullptr and nullptr_t

Nullptr habits are called pointer null values

The nullptr_t habit is called the pointer null type

That is, the pointer null value type is not just one instance of nullptr

You can declare a variable with a pointer to a null value type by nullptr_t

Except for nullptr and nullptr_t, there are various built-in types in C + +.

The C++11 standard strictly specifies the relationship between the data. The common rules are simple as follows:

1. All data defined as nullprt_t type is equivalent and behaves exactly the same

2. nullprt_t type data can be implicitly converted to any pointer type

3. nullptr_t type data cannot be converted to a non-pointer type.

Even using reinterpret_cast<nullptr_t> is not possible.

4. nullptr_t type data does not apply to arithmetic operation expressions

5. nullptr_t type data can be used for relational operation expressions,

But can only be compared with nullptr_t type data or pointer type data

Returns True when and only if the relational operator is ==,<=,>=, etc.

The sample code is as follows:

1#include <iostream>2 using namespacestd;3 4 voidFunintN) {cout <<"Fun (int n):"<< N <<Endl;};5 voidFunint*p) {cout <<"Fun (int *p):"<< P <<Endl;};6 7 voidMain ()8 {9     intNzero =0;Ten     intNvalue = NULL;//OK One     int*pzero =0;//OK A     int*pnull = NULL;//OK -     int*pnullptr = nullptr;//OK -     void*pempty = nullptr;//OK the  - //int ntemp = nullptr; //Error -     /* - the compilation error message for this statement is as follows: + error C2440: "Initialize": Cannot convert from "nullptr" to "int" - native nullptr can only be converted to bool or converted to integers using reinterpret_cast +     */ A     BOOLBIs =nullptr; at     intNtemp = reinterpret_cast<int>(nullptr); -  -Fun0);//-Fun (int n): 0 -Fun (NULL);//-->fun (int n): 0 -Fun ((int*)0);//-->fun (int *p): 00000000 -Fun (nullptr);//-->fun (int *p): 00000000 in  - nullptr_t pnull; toFun (Pnull);//-->fun (int *p): 00000000 +  -     Char* Pchar =Pnull; the     int* PInt =Pnull; *  $ //int n1 = pnull;Panax Notoginseng //int n2 = reinterpret_cast<int>pnull; -  the     if(0==nullptr) +     {} A //if (nullptr) the //    {} +  - //nullptr + = 1; $ //Pnull * TEN; $  -cout <<sizeof(nullptr) << Endl;//4 -}

Good good Study, day.

Sequential Selection Cycle Summary

C++11---nullptr