Template operators

[D-Dog]

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>*,

__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

 

[Marcel Müller]

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

 

[Rolf Magnus]

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>*,

__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.

 

[D-Dog]

The signature is wrong. Use:

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




Same here, but vector depend on correct signature.

Marcel

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

 

[D-Dog]

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>*,

__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 help.