I just learned C++, and I don't understand the below:
The code part:
int *i = new int;
*i = 0;
int &j = *i;
j++;
Question: which the meaning of the last line: j++?
Answer: Increments the value pointed to by i by one.
My confusion:
I am not sure the meaning of int &j = *i;
What's the relationship between j and pointer i? j is the pointer or other?
I am not sure the meaning of int &j = *i; what's the relationship between j and pointer i? j is the pointer or other?
int &j is declaring a variable j, of type int&, or integer reference (see What is a reference variable in C++?).
int &j = *i is assigning the value at address i to the reference variable j. So whenever you modify j, you'll be modifying *i (and vice versa).
See also: What are the differences between a pointer variable and a reference variable in C++?
I am not sure the meaning of
int &j = *i;
i has been previously initialised as a pointer to a (dynamically allocated using operator new) int. *i is a reference to that same dynamically allocated int.
In the declaration, int &j declares j to be a reference to an int. The = *i causes j to be a reference to the same int as *i.
In subsequent code where j is visible, j is now a reference to (an alternative name, or an alias, for) the int pointed to by i.
Any operation on j will affect that int, in exactly the same way that doing that same operation on *i would.
So, j++ has the effect of post-incrementing *i.
Be aware of rules of operator precedence and associativity though.
++*i and ++j are equivalent because the pre-increment (prefix ++) and * (for pointer dereference) have the same precedence and associativity.*i++ is NOT equivalent to j++, since post-increment (postfix ++) has higher precedence than the *. So *i++ is equivalent to *(i++) but j++ is equivalent to (*i)++.