ptrA = ptrB等同于ptrA =＆* ptrB？，并且空值共享一个地址空间吗？

Question

我有几个关于指针重新分配，指针比较以及是否在Q1，Q2和Q3中分别共享地址空间的问题。

int main() 
{ 
int var2 = 2; 
int varnull = NULL; 
int* myPtr_simple = &var2; 

//Q1) are these 2 statements equivalent in terms of reassigning 
//both myPtr_long and myPtr_short to what myPtr_simple points to? 
int* myPtr_long = &*myPtr_simple; 
int* myPtr_short = myPtr_simple; 

//Q2) are these 2 statements equivalent? 
std::cout<<(myPtr_short==myPtr_long)<<std::endl; //TRUE 
std::cout<<(*myPtr_short==*myPtr_long)<<std::endl; //TRUE 

//if var2 is non-null 
//(address spaces of var2, myPtr_short, myPtr_long are equal) 
std::cout<<(&*myPtr_short==&*myPtr_long)<<std::endl; //TRUE 
std::cout<<(&*myPtr_short==&var2)<<std::endl; //TRUE 
std::cout<<(&var2==&*myPtr_long)<<std::endl; //TRUE 

//Q3) if varnull is null 
//(myPtr_short and myPtr_long share address space, but not same as varnull...why?) 
myPtr_long = NULL; 
myPtr_short = NULL; 
std::cout<<(&*myPtr_short==&*myPtr_long)<<std::endl; //TRUE 
std::cout<<(&*myPtr_short==&varnull)<<std::endl; //FALSE 
std::cout<<(&varnull==&*myPtr_long)<<std::endl; //FALSE 

return 0; 
} 

Answer 1

Q1）是等价的重新分配都myPtr_long和myPtr_short什么myPtr_simple点而言这2条语句？

int* myPtr_long = &*myPtr_simple; 
int* myPtr_short = myPtr_simple; 

是，这些有同样的效果。

Q2）这两个语句是否相等？

std::cout<<(myPtr_short==myPtr_long)<<std::endl; //TRUE 
std::cout<<(*myPtr_short==*myPtr_long)<<std::endl; //TRUE 

不，绝对不是。 myPtr_short==myPtr_long检查myPtr_short和myPtr_long是否是指向同一对象的指针。 （这不完全正确，但现在已足够接近。）*myPtr_short==*myPtr_long检查两个引用的对象是否保持相同的值。

int i = 0, j = 0; 
int* pi = &i; 
int* pj = &j; 

现在，pi == pj是不正确的。 pi和pj指向不同的对象。

但*pi == *pj是真实的，因为两个i和j正好有值0，并且0 == 0显然是正确的。

Q3）如果varnull为空（myPtr_short和myPtr_long共享地址空间，但不一样的varnull ......为什么？）

myPtr_long = NULL; 
myPtr_short = NULL; 
std::cout<<(&*myPtr_short==&*myPtr_long)<<std::endl; //TRUE 
std::cout<<(&*myPtr_short==&varnull)<<std::endl; //FALSE 

&*myPtr_short和&*myPtr_long只是myPtr_short和myPtr_long。他们都是NULL，因为这是你刚刚分配给他们的价值。

&varnull不是NULL：它是一个指向对象的有效指针。您用来初始化该对象的价值无关紧要，因为这不会检查varnull的价值。