Quotes and continuous assignments, thank you!

diamond52

For the form a = b = c, both the return value and the reference can be
For the form (a = b) = c, of course, returning an object is not possible, from another perspective
It can also be explained that because the return value creates a temporary object, and the temporary object is in
C ++ is const. It is not possible to assign to a const quantity.
A detailed explanation is given in "effective C ++" item15, comprehensively used in various situations, for = no other choice,
Returns a reference,
For individual cases, you can use some forms to return objects and the like. Step by step analysis, you can draw conclusions.

diamond52

(a = b) = c
====
In this form, if the return is not a reference, the value of c will not be assigned to either a or b.
If a reference is returned, the value of b is assigned to a, and then the value of c is assigned to a, overwriting the former.
If the object is returned, it cannot be executed first. If it can be executed, then the value of c is assigned to the created temporary object (note the const amount). At this time, it will not be assigned to a, and will not be assigned to b.

diamond52

I think it is clear, waiting for the master to summarize and advise

格里弗斯

But for the case of a = b = c, the return result is incorrect.

diamond52

#include <iostream>
using namespace std;

class A
{
public:
A (int i): a (i) {}
A operator = (const A&ra)
{
a = ra.a;
return * this;
}
void display ()
{
cout << a;
}
private:
int a;
};

int main ()
{
A a (1);
A b (2);
A c (3);

a = b = c;
a.display (); // 3
b.display (); // 3
c.display (); // 3
return 0;
}

diamond52

The simple form of a = b = c is wrong. What's the problem with you?

格里弗斯

Take a look at the link I posted. In the case of returning a value, the values ​​of a and b are both 99. Why is this? I also tried that program. Thank you.

diamond52

int main ()
{
A a (1);
A b (2);
A c (3);

a = b = c;
a.display (); // 3
b.display (); // 3
c.display (); // 3

A d (4);
A e (5);
A f (6);

(d = e) = f;
d.display ();
e.display ();
f.display ();
return 0;
}
Correct a statement. According to the test (d = e), the return value does not seem to be a const temporary object. Theoretically, it should be. Is this a compiler related issue?

diamond52

According to the situation of this test (d = e), the return value does not seem to be a const temporary object. In theory, it should be. Is this something related to the compiler, waiting for expert advice?
Found a gap in understanding, well, wait for the master

diamond52

up