Q139349: FIX: C2607 Error Passing Ref to Pointer w/ Templated Functions
Article: Q139349
Product(s): Microsoft C Compiler
Version(s): 2.0,2.1,2.20
Operating System(s):
Keyword(s):
Last Modified: 03-AUG-2001
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The information in this article applies to:
- Microsoft Visual C++, versions 2.0, 2.1, 2.20
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SYMPTOMS
========
When you pass a reference to a pointer of the templated type, the compiler
incorrectly generates an error at the point where the function is called. The
error is:
C2607: 'initializing' : cannot implicitly convert a '<type>*' to a
'type**& ' that is not const
where <type> represents the data type to which the templated data type is
being instantiated for the function call.
WORKAROUND
==========
You may be able to accomplish the same thing by remembering that pointers are
similar to references, so you may be able to pass a pointer to a pointer instead
of a reference to a pointer. The problem with this is that it requires code
modification at the point where the function is called because you must pass the
address of the pointer. Also, you need to modify the code at any point within
the function where the pointer is referenced, which means that one more level of
de-referencing is required.
If it is not necessary to change the address the pointer points to, an easier
solution is to simply pass the pointer instead of a reference (or pointer) to
the pointer. This workaround requires no code modification at all, but the
address the pointer points to cannot be permanently changed from within the
function.
STATUS
======
Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem was corrected in Microsoft Visual C++,
32 bit edition, version 4.0.
Sample Code to Demonstrate Problem
----------------------------------
/* Compile options needed: None - build the following as a console app
using default options.
*/
#include <iostream.h>
template <class T>
void fn(T*& ptr)
{
*ptr = 71957;
}
void main()
{
int i = 123;
int* ip = &i;
fn(ip); // <=== error C2607: 'initializing' : cannot implicitly
// convert a 'int*' to a 'int**& ' that is not const
cout << *ip << endl;
cin >> i;
}
Example Workaround
------------------
In this case, the address the pointer points to does not need to be permanently
changed, so you could simply remove the ampersane (&) from this line:
void fn(T*& ptr)
This is sufficient to make the program compile and run correctly. If it was
necessary to change the address that ptr points to permanently within the fn
function, you could change it to void fn(T** ptr), and add an additional level
of indirection to every reference of ptr within fn. It would also be necessary
to add the ampersand (&) operator to every call of fn in order to pass the
address of its argument. In the previous code sample, fn(ip) would have to be
changed to fn(&ip).
Additional query words: 2.00 2.10 2.20 9.0 9.00
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Keywords :
Technology : kbVCsearch kbAudDeveloper kbVC200 kbVC210
Version : :2.0,2.1,2.20
Issue type : kbbug
Solution Type : kbfix
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