Hi,
I'm having some trouble overloading the '==' operator. I've snipped
irrelevant parts to demonstrate the problem. Perhaps someone can see
what I'm doing wrong.

I have a template class:

template<class T> class testFile {

private:
T data;
public:

bool operator==(testFile &val) {
return(data == val.data);
}

--------------------------------------------------------

The above works fine for any instance of testFile<{insert data type}>

However, when I do the following

class testFile2 {
private:

std::vector< testFile<{some-data-type}> > testThis;

public:

bool operator==(testFile2 &this_test) {
return(testThis == this_test.testThis);
}
}

I get the following compile error:

/usr/lib/gcc/i386-redhat-linux/3.4.6/../../../../include/c++/3.4.6/
bits/stl_algobase.h: In function `bool std::equal(_InputIterator1,
_InputIterator1, _InputIterator2) [with _InputIterator1 =
__gnu_cxx::__normal_iterator<const testFile<float>*,
std::vector<testFile<float>, std::allocator<testFile<float> > > >,
_InputIterator2 = __gnu_cxx::__normal_iterator<const testFile<float>*,
std::vector<testFile<float>, std::allocator<testFile<float> > > >]':
/usr/lib/gcc/i386-redhat-linux/3.4.6/../../../../include/c++/3.4.6/
bits/stl_vector.h:878: instantiated from `bool std:perator==(const
std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)[with _Tp =
testFile<float>, _Alloc = std::allocator<testFile<float> >]'
.../../src/include/../testFile2.h:24: instantiated from here
/usr/lib/gcc/i386-redhat-linux/3.4.6/../../../../include/c++/3.4.6/
bits/stl_algobase.h:691: error:no match for 'operator==' in
'(&__first1)->__gnu_cxx::__normal_iterator<_Iterator,
_Container>:perator* [with _Iterator = const testFile<float>*,
_Container = std::vector<testFile<float>,
std::allocator<testFile<float> > >]() == (&__first2)-
>__gnu_cxx::__normal_iterator<_Iterator, _Container>:perator* [with
_Iterator = const testFile<float>*, _Container =
std::vector<testFile<float>, std::allocator<testFile<float> > >]()'
/../../src/include/../testFile.h:24: note: candidates are: bool
testFile<T>:perator==(testFile<T>&) [with T = float]

Apparently the vector is having some trouble in its operator locating
the proper template operator. Any idea how to handle this?

Thanks,

Dennis

D-Dog wrote:
> bool operator==(testFile &val) {
> return(data == val.data);
> }

The signature is wrong. Use:

bool operator==(const testFile &val) const {


> However, when I do the following
>
> class testFile2 {
> private:
>
> std::vector< testFile<{some-data-type}> > testThis;
>
> public:
>
> bool operator==(testFile2 &this_test) {
> return(testThis == this_test.testThis);
> }

Same here, but vector depend on correct signature.


Marcel

D-Dog wrote:

> Hi,
> I'm having some trouble overloading the '==' operator. I've snipped
> irrelevant parts to demonstrate the problem. Perhaps someone can see
> what I'm doing wrong.
>
> I have a template class:
>
> template<class T> class testFile {
>
> private:
> T data;
> public:
>
> bool operator==(testFile &val) {
> return(data == val.data);
> }

So this operator claims to modify both the left hand and the right hand
operand.


> bits/stl_algobase.h:691: error:no match for 'operator==' in
> '(&__first1)->__gnu_cxx::__normal_iterator<_Iterator,
> _Container>:perator* [with _Iterator = const testFile<float>*,
> _Container = std::vector<testFile<float>,
> std::allocator<testFile<float> > >]() == (&__first2)-
>>__gnu_cxx::__normal_iterator<_Iterator, _Container>:perator* [with
> _Iterator = const testFile<float>*, _Container =
> std::vector<testFile<float>, std::allocator<testFile<float> > >]()'
> /../../src/include/../testFile.h:24: note: candidates are: bool
> testFile<T>:perator==(testFile<T>&) [with T = float]
>
> Apparently the vector is having some trouble in its operator locating
> the proper template operator.

Because there isn't one. It's searching for an operator that does not modify
its operands.

> Any idea how to handle this?

Make your operator:

bool operator==(const testFile &val) const {
return(data == val.data);
}

And read up on const correct programming.

On Apr 7, 11:23 am, Marcel Müller <news.5.ma...@spamgourmet.org>
wrote:
> D-Dog wrote:
> > bool operator==(testFile &val) {
> > return(data == val.data);
>
> > }
>
> The signature is wrong. Use:
>
> bool operator==(const testFile &val) const {
>
> > However, when I do the following
>
> > class testFile2 {
> > private:
>
> > std::vector< testFile<{some-data-type}> > testThis;
>
> > public:
>
> > bool operator==(testFile2 &this_test) {
> > return(testThis == this_test.testThis);
> > }
>
> Same here, but vector depend on correct signature.
>
> Marcel

Won't using a const lead to a "discards qualifier" error when trying
to compile?

On Apr 7, 11:34 am, Rolf Magnus <ramag...@t-online.de> wrote:
> D-Dog wrote:
> > Hi,
> > I'm having some trouble overloading the '==' operator. I've snipped
> > irrelevant parts to demonstrate the problem. Perhaps someone can see
> > what I'm doing wrong.
>
> > I have a template class:
>
> > template<class T> class testFile {
>
> > private:
> > T data;
> > public:
>
> > bool operator==(testFile &val) {
> > return(data == val.data);
> > }
>
> So this operator claims to modify both the left hand and the right hand
> operand.
>
> > bits/stl_algobase.h:691: error:no match for 'operator==' in
> > '(&__first1)->__gnu_cxx::__normal_iterator<_Iterator,
> > _Container>:perator* [with _Iterator = const testFile<float>*,
> > _Container = std::vector<testFile<float>,
> > std::allocator<testFile<float> > >]() == (&__first2)-
> >>__gnu_cxx::__normal_iterator<_Iterator, _Container>:perator* [with
> > _Iterator = const testFile<float>*, _Container =
> > std::vector<testFile<float>, std::allocator<testFile<float> > >]()'
> > /../../src/include/../testFile.h:24: note: candidates are: bool
> > testFile<T>:perator==(testFile<T>&) [with T = float]
>
> > Apparently the vector is having some trouble in its operator locating
> > the proper template operator.
>
> Because there isn't one. It's searching for an operator that does not modify
> its operands.
>
> > Any idea how to handle this?
>
> Make your operator:
>
> bool operator==(const testFile &val) const {
> return(data == val.data);
> }
>
> And read up on const correct programming.

The second const was the key. Thanks for your .

D-Dog wrote:
> On Apr 7, 11:23 am, Marcel Müller <news.5.ma...@spamgourmet.org>
> wrote:
>> D-Dog wrote:
>>> bool operator==(testFile &val) {
>>> return(data == val.data);
>>
>> > }
>>
>> The signature is wrong. Use:
>>
>> bool operator==(const testFile &val) const {
>>
>>> However, when I do the following
>>
>>> class testFile2 {
>>> private:
>>
>>> std::vector< testFile<{some-data-type}> > testThis;
>>
>>> public:
>>
>>> bool operator==(testFile2 &this_test) {
>>> return(testThis == this_test.testThis);
>>> }
>>
>> Same here, but vector depend on correct signature.
>>
>> Marcel
>
> Won't using a const lead to a "discards qualifier" error when trying
> to compile?

(a) Why don't you try it and see?
(b) Why would it "discard" qualifier? Are you using "T" with the
operator== that requires it to be non-const?

V
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