From:

SG <s.gesemann@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 10 May 2009 10:50:01 -0700 (PDT)

Message-ID:

<b2140b9b-e5a2-49b9-af3d-fa83397d4612@v4g2000vba.googlegroups.com>

I understand more about references than it appears. Suppose int& f

(int, int) is a function that returns a reference to a static local

variable. Then f(x,y) == f(a,b) is always true for all integers

x,y,a,b .

(int, int) is a function that returns a reference to a static local

variable. Then f(x,y) == f(a,b) is always true for all integers

x,y,a,b .

No. This is not true for this function:

int& f(int a, int b) {

static int p = 3;

static int q = 4;

if (((p^q) & 1)==0) return p;

return q;

}

int main() {

assert( f(0,0) == f(0,1) ); // fails

}

I'm not clear exactly why although I've seen several

attempts to explain it.

attempts to explain it.

People tried to explain because you don't seem to understand

references. Once a reference has been initialized the reference will

be just another name for the object it refers to. So, if you use the

equality comparison you'll be comparing the values of the aliased

objects and not their addresses. Here are a bunch of other examples:

int main() {

int i = 23;

int j = 23;

int& x = i; // x is an alias for i

int& y = j; // y is an alias for j

assert( x == y); // #1

assert(&x != &y); // #2

assert(&x == &i); // #3

assert(&y == &j); // #4

x = 42;

assert( x != y); // #5

assert(&x != &y); // #2

assert(&x == &i); // #3

assert(&y == &j); // #4

}

1. x and y refer to variables of the same value (23)

2. x and y refer to different variables

3. x refers to i

4. y refers to j

5. x and y refer to variables of different values (23,42)

Cheers!

SG

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