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From: 3DCoderGuy on 7 May 2008 19:49
This is my XYZ_POINT.h file

template<typename T>
class XYZ_POINT
{
private:
T x;
T y;
T z;
public:
XYZ_POINT(void) {};
XYZ_POINT(const T allVals) : x(allVals), y(allVals), z(allVals) {};
bool const operator==(const XYZ_POINT<T> &xyzTest);
}

In my cpp file I have this.
template<typename T>
bool const XYZ_POINT<T>::operator ==(const XYZ_POINT<T> &xyzTest)
{
return ((x == xyzTest.GetX()) &&(y == xyzTest.GetY()) &&(z ==
xyzTest.GetZ()));
}

In the main file I have this

int _tmain(int arc, _TCHAR* argv[])
{
XYZ_POINT<double> dXYZPnt1(1,0,0);
XYZ_POINT<double> dXYZPnt2(3,0,0);

if (dXYZPnt1 == dXYZPnt2)
{
bool b = true;
b = false;
}
}

Doesn't compile with the following error
error LNK2019: unresolved external symbol "public: bool const __thiscall
XYZ_POINT<double>::operator==(class XYZ_POINT<double> const &)"
(??8?$XYZ_POINT@N@@QAE?B_NABV0@@Z) referenced in function _main

If I move the implimentation to the header file it compiles fine.

What am I doing wrong?

The actual implimentation is more complex then I'm demonstrating and I need
to include some header files that I don't want in the declaration.

Thanks

Mark


From: Alf P. Steinbach on 7 May 2008 20:59
* 3DCoderGuy:
> This is my XYZ_POINT.h file
>
> template<typename T>
> class XYZ_POINT
> {
> private:
> T x;
> T y;
> T z;
> public:
> XYZ_POINT(void) {};
> XYZ_POINT(const T allVals) : x(allVals), y(allVals), z(allVals) {};
> bool const operator==(const XYZ_POINT<T> &xyzTest);
> }
>
> In my cpp file I have this.
> template<typename T>
> bool const XYZ_POINT<T>::operator ==(const XYZ_POINT<T> &xyzTest)
> {
> return ((x == xyzTest.GetX()) &&(y == xyzTest.GetY()) &&(z ==
> xyzTest.GetZ()));
> }
>
> In the main file I have this
>
> int _tmain(int arc, _TCHAR* argv[])
> {
> XYZ_POINT<double> dXYZPnt1(1,0,0);
> XYZ_POINT<double> dXYZPnt2(3,0,0);
>
> if (dXYZPnt1 == dXYZPnt2)
> {
> bool b = true;
> b = false;
> }
> }
>
> Doesn't compile with the following error
> error LNK2019: unresolved external symbol "public: bool const __thiscall
> XYZ_POINT<double>::operator==(class XYZ_POINT<double> const &)"
> (??8?$XYZ_POINT@N@@QAE?B_NABV0@@Z) referenced in function _main
>
> If I move the implimentation to the header file it compiles fine.
>
> What am I doing wrong?

Quite a lot. But to answer directly what you're probably most interested in, see

<http://www.parashift.com/c++-faq-lite/templates.html#faq-35.12>.

It's very often a good idea to check the C++ FAQ before asking.

Now as to other wrongdoings.

The class name XYZ_POINT, in all uppercase, is an invitation to name clashes
with macros, and besides it hurts the eyes and ears (all uppercase is perceived
as shouting and is visually distracting). Preferentially reserve all uppercase
names for macros, and make sure that your own macros are always defined with all
uppercase names. That way you minimize the chance of macro name clashes.

Using 'void' to indicate "no arguments": this is a C-ism, not meaningful in C++.

Declaring and defining a default constructor that does not initialize the
members: they will have arbitrary (formally invalid) values.

Semicolon after closing '}' of function definition.

Defining a copy constructor when the one you get by default is just fine.

Not defining operator<, which is the one you really need for algorithms,
containers etc.

Missing semicolon after closing '}' of class definition.

"int _tmain(int arc, _TCHAR* argv[])". This is something some Microsoft
employee scooped up from drainage system and it smelled so bad that all her
co-workers just loved it, and even though they failed to find any reasonable use
for it they just added it everywhere, luv it luv it. Standard for what you need
here is "int main()".

Style: "if( something ) { assign to boolean }". Instead do "boolean =
something". I'm assuming the intent was not to have the boolean as a local
variable.


> The actual implimentation is more complex then I'm demonstrating and I need
> to include some header files that I don't want in the declaration.

When you fix your "main" the above code does not need any headers.


Cheers, & hth.,

- Alf


--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
From: David Wilkinson on 7 May 2008 21:03
3DCoderGuy wrote:
> This is my XYZ_POINT.h file
>
> template<typename T>
> class XYZ_POINT
> {
> private:
> T x;
> T y;
> T z;
> public:
> XYZ_POINT(void) {};
> XYZ_POINT(const T allVals) : x(allVals), y(allVals), z(allVals) {};
> bool const operator==(const XYZ_POINT<T> &xyzTest);
> }
>
> In my cpp file I have this.
> template<typename T>
> bool const XYZ_POINT<T>::operator ==(const XYZ_POINT<T> &xyzTest)
> {
> return ((x == xyzTest.GetX()) &&(y == xyzTest.GetY()) &&(z ==
> xyzTest.GetZ()));
> }
>
> In the main file I have this
>
> int _tmain(int arc, _TCHAR* argv[])
> {
> XYZ_POINT<double> dXYZPnt1(1,0,0);
> XYZ_POINT<double> dXYZPnt2(3,0,0);
>
> if (dXYZPnt1 == dXYZPnt2)
> {
> bool b = true;
> b = false;
> }
> }
>
> Doesn't compile with the following error
> error LNK2019: unresolved external symbol "public: bool const __thiscall
> XYZ_POINT<double>::operator==(class XYZ_POINT<double> const &)"
> (??8?$XYZ_POINT@N@@QAE?B_NABV0@@Z) referenced in function _main
>
> If I move the implimentation to the header file it compiles fine.
>
> What am I doing wrong?
>
> The actual implimentation is more complex then I'm demonstrating and I need
> to include some header files that I don't want in the declaration.

Mark:

Template function/member definitions must be visible to the caller, so they must
be in the .h file. This has nothing to do with operator ==() in particular.

--
David Wilkinson
Visual C++ MVP
From: Alexander Grigoriev on 7 May 2008 23:52
And, by the way, you want the operator== to be const. Not returning const
bool, which doesn't make sense.

bool operator==(const XYZ_POINT<T> &xyzTest) const;

"3DCoderGuy" <nobody(a)nospam.com> wrote in message
news:uzopyzJsIHA.4476(a)TK2MSFTNGP06.phx.gbl...
> This is my XYZ_POINT.h file
>
> template<typename T>
> class XYZ_POINT
> {
> private:
> T x;
> T y;
> T z;
> public:
> XYZ_POINT(void) {};
> XYZ_POINT(const T allVals) : x(allVals), y(allVals), z(allVals) {};
> bool const operator==(const XYZ_POINT<T> &xyzTest);
> }
>
> In my cpp file I have this.
> template<typename T>
> bool const XYZ_POINT<T>::operator ==(const XYZ_POINT<T> &xyzTest)
> {
> return ((x == xyzTest.GetX()) &&(y == xyzTest.GetY()) &&(z ==
> xyzTest.GetZ()));
> }
>
> In the main file I have this
>
> int _tmain(int arc, _TCHAR* argv[])
> {
> XYZ_POINT<double> dXYZPnt1(1,0,0);
> XYZ_POINT<double> dXYZPnt2(3,0,0);
>
> if (dXYZPnt1 == dXYZPnt2)
> {
> bool b = true;
> b = false;
> }
> }
>
> Doesn't compile with the following error
> error LNK2019: unresolved external symbol "public: bool const __thiscall
> XYZ_POINT<double>::operator==(class XYZ_POINT<double> const &)"
> (??8?$XYZ_POINT@N@@QAE?B_NABV0@@Z) referenced in function _main
>
> If I move the implimentation to the header file it compiles fine.
>
> What am I doing wrong?
>
> The actual implimentation is more complex then I'm demonstrating and I
> need to include some header files that I don't want in the declaration.
>
> Thanks
>
> Mark
>
>


From: 3DCoderGuy on 8 May 2008 11:17
"David Wilkinson" <no-reply(a)effisols.com> wrote in message
news:%23bvicdKsIHA.552(a)TK2MSFTNGP06.phx.gbl...
> 3DCoderGuy wrote:
>> This is my XYZ_POINT.h file
>>
>> template<typename T>
>> class XYZ_POINT
>> {
>> private:
>> T x;
>> T y;
>> T z;
>> public:
>> XYZ_POINT(void) {};
>> XYZ_POINT(const T allVals) : x(allVals), y(allVals), z(allVals) {};
>> bool const operator==(const XYZ_POINT<T> &xyzTest);
>> }
>>
>> In my cpp file I have this.
>> template<typename T>
>> bool const XYZ_POINT<T>::operator ==(const XYZ_POINT<T> &xyzTest)
>> {
>> return ((x == xyzTest.GetX()) &&(y == xyzTest.GetY()) &&(z ==
>> xyzTest.GetZ()));
>> }
>>
>> In the main file I have this
>>
>> int _tmain(int arc, _TCHAR* argv[])
>> {
>> XYZ_POINT<double> dXYZPnt1(1,0,0);
>> XYZ_POINT<double> dXYZPnt2(3,0,0);
>>
>> if (dXYZPnt1 == dXYZPnt2)
>> {
>> bool b = true;
>> b = false;
>> }
>> }
>>
>> Doesn't compile with the following error
>> error LNK2019: unresolved external symbol "public: bool const __thiscall
>> XYZ_POINT<double>::operator==(class XYZ_POINT<double> const &)"
>> (??8?$XYZ_POINT@N@@QAE?B_NABV0@@Z) referenced in function _main
>>
>> If I move the implimentation to the header file it compiles fine.
>>
>> What am I doing wrong?
>>
>> The actual implimentation is more complex then I'm demonstrating and I
>> need to include some header files that I don't want in the declaration.
>
> Mark:
>
> Template function/member definitions must be visible to the caller, so
> they must be in the .h file. This has nothing to do with operator ==() in
> particular.
>
> --
> David Wilkinson
> Visual C++ MVP

Thanks David,
This is my first go at templates. I was trying to convert some old classes
over since it just made sence.

Thanks again.


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