default parameter to NULL

[Gary Wessle]

I have a method with the last arguments having defaults like this

void filing(long, double,
const myType& r_mo=NULL,
const herType& r_tr=NULL);

is that acceptable, if not how is it done?
when I do the above, I get errors like

file.h:19: error: default argument for parameter of type ‘const myType&’ has type ‘int’
file.h:20: error: default argument for parameter of type ‘const herType&’ has type ‘int’

[Jim Langston]

Re: default parameter to NULL

"Gary Wessle" <phddas@yahoo.c omwrote in message
news:m34prp959a .fsf@localhost. localdomain...

>
I have a method with the last arguments having defaults like this
>
void filing(long, double,
const myType& r_mo=NULL,
const herType& r_tr=NULL);
>
is that acceptable, if not how is it done?
when I do the above, I get errors like
>
file.h:19: error: default argument for parameter of type 'const myType&'
has type 'int'
file.h:20: error: default argument for parameter of type 'const herType&'
has type 'int'

A reference can't have a NULL value, one reason being becasue you can't
check for it. You can do that with a pointer, but not a reference.

[Greg]

Re: default parameter to NULL

Gary Wessle wrote:

I have a method with the last arguments having defaults like this
>
void filing(long, double,
const myType& r_mo=NULL,
const herType& r_tr=NULL);
>
is that acceptable, if not how is it done?
when I do the above, I get errors like

No, it is not reasonable to attempt to pass NULL for any parameter
declared a reference - a reference requires that the caller always
supply an object (of a suitable type) in order to call the function.

To indicate that values for myType and herType are not required in
order to call filing(), there are a few options available. One approach
is for filing to accept pointers instead of references for those
values:

void filing( long, double,
const myType* r_mo = NULL,
const herType* r_tr = NULL);

A better approach would probably be to overload filing() - with one
overload accepting the two reference parameters and another overload of
filing() that does not:

void filing( long, double, const myType& r_mo, const herType&);
void filing( long, double);

Greg

[zhao.kaiyong@gmail.com]

Re: default parameter to NULL


"Greg дµÀ£º
"

Gary Wessle wrote:

I have a method with the last arguments having defaults like this

void filing(long, double,
const myType& r_mo=NULL,
const herType& r_tr=NULL);

is that acceptable, if not how is it done?
when I do the above, I get errors like

>
No, it is not reasonable to attempt to pass NULL for any parameter
declared a reference - a reference requires that the caller always
supply an object (of a suitable type) in order to call the function.
>
To indicate that values for myType and herType are not required in
order to call filing(), there are a few options available. One approach
is for filing to accept pointers instead of references for those
values:
>
void filing( long, double,
const myType* r_mo = NULL,
const herType* r_tr = NULL);
>
A better approach would probably be to overload filing() - with one
overload accepting the two reference parameters and another overload of
filing() that does not:
>
void filing( long, double, const myType& r_mo, const herType&);
void filing( long, double);

Greg

I agree with you.