I have a situation where the wrong constructor is being called. I
have defined 2 constructors with different parameter types that are
defined as follows...
class __declspec(dlle xport)CColumn : public CColumnBase
{
public:
CColumn(CString columnType,CObj ect *aOwner, CString anId);
CColumn(CString columnType,CObj ect *aOwner, bool batchUpdated);
....
}
The implementation of these functions looks like this...
CColumn::CColum n(CString columnType, CObject *aOwner, CString anId)
{
setColumnType(c olumnType);
setOwner(aOwner );
setId(anId);
setLength(10);
setPrecision(5) ;
setField();
setBatchUpdated (false);
}
CColumn::CColum n(CString columnType, CObject *aOwner, bool
batchUpdated)
{
setColumnType(c olumnType);
setOwner(aOwner );
setId("");
setLength(10);
setPrecision(5) ;
setField();
setBatchUpdated (batchUpdated);
}
When the line below in the CDual() constructor gets called, the
constructor with the signature of CColumn::CColum n(CString columnType,
CObject *aOwner, bool batchUpdated) gets invoked, rather than the one
I want.
//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////
IMPLEMENT_DYNCR EATE( CDual, CDomain )
CDual::CDual()
{
...
addColumn(new CColumn(TIMESTA MP_COLUMN,this, "TIMESTAMP" ));
...
}
Does anyone have any idea why this is happening and how to avoid this
issue?
Thanks,
Joe
17  1662 
"Joe" <jr*****@purina .com> wrote in message news:ec******** *************** ***@posting.goo gle.com... When the line below in the CDual() constructor gets called, the
constructor with the signature of CColumn::CColum n(CString columnType,
CObject *aOwner, bool batchUpdated) gets invoked, rather than the one
I want.
Because the bool is a better match for char* than CString is. Any pointer
can be converted to bool, and that is a standard conversion sequence.
I assume CString has a converting constructor that takes a char*. This
is a user-defined conversion sequence. The standard conversion sequence
wins out.
You'll either have to make your overloads less ambiguous, or explicitly do
something to the call to make it not match bool (like converting it to CString yourself).
new CColumn(TIMESTA MP_COLUMN, this, CString("TIMEST AMP"));
Joe wrote:
CDual::CDual()
{
...
addColumn(new CColumn(TIMESTA MP_COLUMN,this, "TIMESTAMP" ));
...
}
Does anyone have any idea why this is happening
I am not sure if this is a compiler bug or not.
But obviously the compiler prevers the conversion
from a character pointer to a bool over the construction
of a temporary object.
and how to avoid this
issue?
Simple. Force the compiler to do it:
{
...
addColumn(new CColumn(TIMESTA MP_COLUMN,this, CString( "TIMESTAMP" )));
...
}
another workaround would be to introduce a third constructor which
takes a const char*
--
Karl Heinz Buchegger kb******@gascad .at
"Ron Natalie" <ro*@sensor.com > wrote in message
news:40******** *************@n ews.newshosting .com...
"Joe" <jr*****@purina .com> wrote in message
news:ec******** *************** ***@posting.goo gle.com... When the line below in the CDual() constructor gets called, the
constructor with the signature of CColumn::CColum n(CString columnType,
CObject *aOwner, bool batchUpdated) gets invoked, rather than the one
I want.
Because the bool is a better match for char* than CString is. Any
pointer can be converted to bool, and that is a standard conversion sequence.
I assume CString has a converting constructor that takes a char*. This
is a user-defined conversion sequence. The standard conversion sequence
wins out.
Is this true for the language as part of the standard, or is it compiler
dependent and you're inferring that's his implementation?
"Joe" <jr*****@purina .com> wrote in message
news:ec******** *************** ***@posting.goo gle.com... I have a situation where the wrong constructor is being called. I
have defined 2 constructors with different parameter types that are
defined as follows...
class __declspec(dlle xport)CColumn : public CColumnBase
{
public:
CColumn(CString columnType,CObj ect *aOwner, CString anId);
CColumn(CString columnType,CObj ect *aOwner, bool batchUpdated);
...
}
[SNIP implementation details]
CDual::CDual()
{
...
addColumn(new CColumn(TIMESTA MP_COLUMN,this, "TIMESTAMP" ));
...
}
Does anyone have any idea why this is happening and how to avoid this
issue?
Thanks,
Joe
It's because you aren't calling the constructor with a (CString) - you are
calling it with "TIMESTAMP" which is a (char const*). There is a
language-defined conversion from a pointer to a bool (non-NULL -> true,
NULL -> false), which beats out the user-defined conversion from (char
const*) to (CString). I don't remember the exact language rule here, but
it's come up in my code before. You have several options:
1) Instead call CColumn (TIMESTAMP_COLU MN, this, CString ("TIMESTAMP" ));
2) Create a new constructor CColumn (CString columnType,CObj ect *aOwner,
char const *anId);
3) Change the argument orders, or add an argument to a constructor.
4) Use the named constructor idiom. (static CColumn *createById (...);
static CColumn *createBatch (...).
5) Passing a bool to a constructor is often a hint to break the class into
two, using polymorphism.
What you do depends on several factors, including what code is yours. I
don't recall if CColumn is an MFC class or not.
HTH
--
KCS
"Karl Heinz Buchegger" <kb******@gasca d.at> wrote in message news:40******** *******@gascad. at... I am not sure if this is a compiler bug or not.
But obviously the compiler prevers the conversion
from a character pointer to a bool over the construction
of a temporary object.
It's not a bug. The conversion of a pointer to bool is a standard
conversion sequence. The conversion to CString is a user-defined
conversion. A standard conversion sequence is preferred over a
user-defined conversion. That's the language.
"jeffc" <no****@nowhere .com> wrote in message news:40******** @news1.prserv.n et... Is this true for the language as part of the standard, or is it compiler
dependent and you're inferring that's his implementation?
It's the way the C++ language works. There's nothing wrong
with his compiler in this regard.
Ron Natalie wrote:
"Karl Heinz Buchegger" <kb******@gasca d.at> wrote in message news:40******** *******@gascad. at... I am not sure if this is a compiler bug or not.
But obviously the compiler prevers the conversion
from a character pointer to a bool over the construction
of a temporary object.
It's not a bug. The conversion of a pointer to bool is a standard
conversion sequence. The conversion to CString is a user-defined
conversion. A standard conversion sequence is preferred over a
user-defined conversion. That's the language.
Thank's for clearification.
--
Karl Heinz Buchegger kb******@gascad .at
"Joe" <jr*****@purina .com> wrote in message
news:ec******** *************** ***@posting.goo gle.com... I have a situation where the wrong constructor is being called. I
have defined 2 constructors with different parameter types that are
defined as follows...
[SNIP] Does anyone have any idea why this is happening and how to avoid this
issue?
This is a problem of the conversion sequence. The standard states that the
order of conversions are 1. standard-conversion, 2. user defined
conversions, 3. elipsis conversions. The conversion to bool is a valid
standard conversion for any pointer as it is indicated in section 4.12 of
the standard. CString has a ctor enable implicit user conversions for string
literals. However, the standard conversion to bool wins due to the ordering.
What you have to do is to disamiguate the ctor call by supplying a CString
object as the 3rd parameter or provide another ctor which can take a const
char*.
Regards
Chris
"jeffc" <no****@nowhere .com> wrote in message
news:40******** @news1.prserv.n et...
"Ron Natalie" <ro*@sensor.com > wrote in message
news:40******** *************@n ews.newshosting .com...
"Joe" <jr*****@purina .com> wrote in message
news:ec******** *************** ***@posting.goo gle.com... When the line below in the CDual() constructor gets called, the
constructor with the signature of CColumn::CColum n(CString columnType,
CObject *aOwner, bool batchUpdated) gets invoked, rather than the one
I want.
Because the bool is a better match for char* than CString is. Any
pointer can be converted to bool, and that is a standard conversion sequence.
I assume CString has a converting constructor that takes a char*. This
is a user-defined conversion sequence. The standard conversion
sequence wins out.
Is this true for the language as part of the standard, or is it compiler
dependent and you're inferring that's his implementation?
It's defined by the standard in section 13.3.3.1 (ISO:IEC 14882:1998(E))
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