c ++概念帮助,指针

Question

所以我对指针有一个合理的理解,但我被问到这些是什么区别:

void print(int* &pointer)

void print(int* pointer)

我自己还是学生,我不是100%.我很抱歉,如果这是基本但我的googleing技能让我失望.无论如何,你可以帮助我更好地理解这个概念.我很久没有使用过c ++了,我正在努力帮助一个学生,我正在努力为她巩固我的概念知识.

Answer 1

第一个通过引用传递指针,第二个按值传递.

如果使用第一个签名,则可以修改指针指向的内存以及指向的内存.

例如:

void printR(int*& pointer)   //by reference
{
   *pointer = 5;
   pointer = NULL;
}
void printV(int* pointer)    //by value
{
   *pointer = 3;
   pointer = NULL;
}

int* x = new int(4);
int* y = x;

printV(x);
//the pointer is passed by value
//the pointer itself cannot be changed
//the value it points to is changed from 4 to 3
assert ( *x == 3 );
assert ( x != NULL );

printR(x);
//here, we pass it by reference
//the pointer is changed - now is NULL
//also the original value is changed, from 3 to 5
assert ( x == NULL );    // x is now NULL
assert ( *y = 5 ;)