comma operator

[bb]

Hi,

Please could someone throw some light on why the following definitions
are not the same?

class A {

const int& a, b; // b does not get defined as a
ref. but a plain int

const int& x; const int& y; // obviously, both are refs.

...

};

Thanks.

 

[Victor Bazarov]

Please could someone throw some light on why the following definitions
are not the same?

class A {

const int& a, b; // b does not get defined as a
ref. but a plain int

const int& x; const int& y; // obviously, both are refs.

...

};

It really has nothing to do with comma operator, you know.

The rules of declarations are such that '*' and '&' are part of the
individual object declaration, whereas the type (the 'const int' part
in your example) is common for all objects. IOW, the same thing would
happen if you declared 'a' as a pointer to const int:

const int* a, b; // 'a' is a pointer, 'b' is not.

To avoid mistakes like that, declare each object in its own separate
statement, or use typedefs:

typedef const int *pointerToConstInt;

pointerToConstInt a, b; // both 'a' and 'b' are pointers now

V

 

[Supat Wongwirawat]

It is the C++ syntax.
For reference and pointer you cannot declare like this

T& a,b,c;
T* a,b,c;

Only a will be reference/ pointer.
You have to specify * or & for every variable in the declaration.

const int &a, &b; will do what you want to accomplish.

Hope that helps.

 

[bb]

Thanks guys for the explanation.

 

[Default User]

It is the C++ syntax.

Please don't top-post. Your replies belong following or interspersed
with properly trimmed quotes. See the majority of other posts in the
newsgroup, or the group FAQ list:
<http://www.parashift.com/c++-faq-lite/how-to-post.html>

 

[Tomás Ó hÉilidhe]

bb:

const int& a, b; // b does not get defined as a
ref. but a plain int

const int& x; const int& y; // obviously, both are refs.

In the "grammar" of C++, the ampersand and the asterisk are part of the
object's name rather than its type. That's why I write: int *p instead of
int* p.

Write a type, then write the names after it, separated by commas:

int *a, *b, *c, *d;

This grammar is what leads to declarations such as:

int (*p(double))[5];

Also don't confuse the comma within structs with the _actual_ comma
operator.