Reference question

LiYS

It is said that "Once a reference is initialized to an object, it cannot be changed to refer to another object." But does this only apply locally. The following codes can compile successfully inside function which is controdict with the rule

int x;
int y;
int& r = x;
r = y;

----------- Another question

extern class A;
void h(A*& a)
{
...
}
int main() {
A a;
h(&a); // Error ,Line# 2
A *b = New A;
h(b) // Correct

Why line 2 can't pass the compilation? I see no difference between "&a" and "b"

Bhaskar

There's no contradiction. Check this modified code int x = 10; int y = 20; int& r = x; // make r refer to x r = y; // this does not change the reference, value of y is copied to r, i.e., to x r += 10; // this will modify x, not y, because r still refers to x, not y cout << r << " " << x << " " << y ; // prints 30 30 20 For the second one, you have created reference to a pointer in the function parameter A*& a. By this it means a refers to a pointer of type A which it can modify. However when you pass &a to the function h, &a is not modifiable. Check this sample code A a1, a2; A* p1; A* &r1 = p1; // Ok, r1 refers to a modifiable pointer p1 p1 = &a1; // p1 points to a1 r1 = &a2; // now p1 points to a2 A* &r2 = &a2; // ERROR: &a2 is not modifiable, &a2 is a constant pointer

LiYS

I see your point.

int x = 3;
int y = 1;
int& r = x;
r = y;

int main() {}

The above codes can't pass the compilation and with a error message "'r' : missing storage-class or type specifiers", It doesn't make sense to me, here the last line just assign "y" to the object "r" refers which is "x", and when I move it to local function the error disappears, why?

Jose Lamas Rios

YongSheng Li wrote: int x = 3; int y = 1; int& r = x; r = y; int main() {} The first three lines are variable declarations that include their initialization. That's valid at the file scope. The fourth line (r = y;) is an assignment, which is not legal at the file scope; it's only valid in the body of a function. -- jlr http://jlamas.blogspot.com/[^]

S Senthil Kumar

You can only declare and initialize variables outside of functions, you can't write statements like r=y. Regards Senthil _____________________________ My Blog | My Articles | WinMacro

S Senthil Kumar

Beat me to it by a minute :) Regards Senthil _____________________________ My Blog | My Articles | WinMacro

Jose Lamas Rios

It's ok. I'll share the prize with you :) -- jlr http://jlamas.blogspot.com/[^]

LiYS

S. Senthil Kumar wrote: Beat me to it by a minute What that supposed to means?