Python descriptor details

pointer Vs. reference

Firstly, reference is the concept of C++, it is a simple reference data type that is less powerful but safer than the pointer type.

int a=2;
int& ra=a; // define a reference ra
std::cout << ra; // 2

Reference is a sort of alias for the target. For example, ra is a sort of alias for the r in the above example. When we refer to the ra, practically refer to the a. ra and a are conceptually one. Changing ra means changing a, and changing a means changing ra.

Essentially, reference is same as the pointer, reference is the grammar sugar of the pointer.

Because from the assembly code, the implementation of reference is almost same as pointer. Therefore, reference is also need to be allocated the memory.

• Reference is the grammar sugar of the pointer, it is intended as the const pointer which can do the address-of operation(&) and the dereference operation(*) by the compiler.
• Reference must be initialized when it is created, pointer not.
• Reference is a sort of alias of the target, therefore, reference must be non-null, pointer not.
• Reference is the target value execute the increment(++) or decrement(--) operation, but the pointer is itself executes the increment or decrement operation.

Particularly, the reference can be used as the formal parameter to avoid the check of if the passed parameter is 0. For example:

void fun1(int *point)
{
    // need to check whether the point is NULL
     if(!point)
     {
        return;
     }
}

void fun2(int &reference)
{
     // reference is must be non-null 
}

sizeof(*pointer) will get the memory space of a pointer, sizeof(&reference) will get the referenced object’s memory space.

References

• zhihu
• wiki)
• overflow
• assembly perspective

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