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Joe Laughlin
Guest

Posted: Fri Oct 22, 2004 1:02 am Post subject: weird error

(file and class names changed to protect the innocent) g++ -Wall -c file.cpp: In member function `std::string Some_Class::get_member(const std::string&) const': file.cpp:46: passing `const std::map<std::string, std::string, std::less std::string, std::string> > >' as `this' argument of `_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = std::string, _Tp = std::string, _Compare = std::less<std::string>, _Alloc = std::allocator<std::pair]' discards qualifiers I can't make heads or tails of this error. I'm guessing it has something to do with calling a non-const function on some const object. Any ideas? The function SomeClass::get_member is: std::string SomeClass::get_member(const std::string &name) const { return _member[name]; } where _member is a std::map<std::string, std::string>.

Victor Bazarov
Guest

Posted: Fri Oct 22, 2004 2:07 am Post subject: Re: weird error

"Joe Laughlin" <Joseph.V.Laughlin (AT) boeing (DOT) com> wrote...

Quote:

(file and class names changed to protect the innocent)

g++ -Wall -c file.cpp: In member function `std::string
Some_Class::get_member(const std::string&) const':
file.cpp:46: passing `const std::map<std::string,
std::string, std::less std::string, std::string> > >' as `this' argument of `_Tp&
std::map<_Key,
_Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key =
std::string,
_Tp = std::string, _Compare = std::less<std::string>, _Alloc =
std::allocator<std::pair]' discards
qualifiers

I can't make heads or tails of this error. I'm guessing it has something
to
do with calling a non-const function on some const object. Any ideas?

The function SomeClass::get_member is:

std::string SomeClass::get_member(const std::string &name) const
{
return _member[name];
}

where _member is a std::map<std::string, std::string>.

You declared this member function ('get_member') "const". That means that
the object (and all its data member except 'mutable' ones) are not going to
change. Indexing operator for 'map' template is a _non-const_ function.
I.e. it cannot be called for a const map. It has to be non-const because
it may insert a new object if it's not there yet.

You need to either make peace with the fact that it may insert another
object into your _member (and declare '_member' "mutable") or use some other
way. It seems that your function _assumes_ that there is an element with
the
key 'name' in the map. What if there isn't?

Victor

Brian Riis
Guest

Posted: Fri Oct 22, 2004 5:37 am Post subject: Re: weird error

Joe Laughlin wrote:

Quote:

(file and class names changed to protect the innocent)

g++ -Wall -c file.cpp: In member function `std::string
Some_Class::get_member(const std::string&) const':
file.cpp:46: passing `const std::map<std::string,
std::string, std::less std::string, std::string> > >' as `this' argument of `_Tp& std::map<_Key,
_Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = std::string,
_Tp = std::string, _Compare = std::less<std::string>, _Alloc =
std::allocator<std::pair]' discards
qualifiers

I can't make heads or tails of this error. I'm guessing it has something to
do with calling a non-const function on some const object. Any ideas?

The function SomeClass::get_member is:

std::string SomeClass::get_member(const std::string &name) const
{
return _member[name];

Your function is declared const, but you cannot guarantee that the
subscript operator of the map doesn't change the value at 'name'. In
other words: In a const member function you can only use other const
functions (in regard to your own members). In the above, if 'name' does
not exist in _member, *it will be created*. You are not allowed to do
that in a const function.

Quote:

}

try this:

std::string SomeClass::get_member(std::string const & name) const
{
_member.const_iterator it;
it = _member.find(name);
if(it != _member.end())
_return it->second;
else
<...> // Whatever you want to do, if 'name' isn't there...
}

Takes up a bit more space, but it works. On most compilers I should
think it is as efficient too.

--
/Brian Riis

Joe Laughlin
Guest

Posted: Fri Oct 22, 2004 7:03 pm Post subject: Re: weird error

Brian Riis wrote:

Quote:

Joe Laughlin wrote:
(file and class names changed to protect the innocent)

g++ -Wall -c file.cpp: In member function `std::string
Some_Class::get_member(const std::string&) const':
file.cpp:46: passing `const std::map<std::string,
std::string, std::less std::allocator<std::pair std::string> > >' as `this' argument of `_Tp&
std::map<_Key, _Tp, _Compare,
_Alloc>::operator[](const _Key&) [with _Key =
std::string, _Tp = std::string, _Compare =
std::less<std::string>, _Alloc =
std::allocator<std::pair ]' discards qualifiers

I can't make heads or tails of this error. I'm guessing
it has something to do with calling a non-const function
on some const object. Any ideas?

The function SomeClass::get_member is:

std::string SomeClass::get_member(const std::string
&name) const {
return _member[name];

Your function is declared const, but you cannot guarantee
that the subscript operator of the map doesn't change the
value at 'name'. In other words: In a const member
function you can only use other const functions (in
regard to your own members). In the above, if 'name' does
not exist in _member, *it will be created*. You are not
allowed to do that in a const function.

}

try this:

std::string SomeClass::get_member(std::string const &
name) const {
_member.const_iterator it;
it = _member.find(name);
if(it != _member.end())
_return it->second;
else
...> // Whatever you want to do, if 'name' isn't
there... }

Takes up a bit more space, but it works. On most
compilers I should think it is as efficient too.

Thanks you guys.

Is:
_member.const_iterator it;
legal? The compiler didn't like that line, but it did like:
std::map<std::string, std::string>::const_iterator it;

Joe

John Harrison
Guest

Posted: Fri Oct 22, 2004 7:17 pm Post subject: Re: weird error

Quote:

try this:

std::string SomeClass::get_member(std::string const &
name) const {
_member.const_iterator it;
it = _member.find(name);
if(it != _member.end())
_return it->second;
else
...> // Whatever you want to do, if 'name' isn't
there... }

Takes up a bit more space, but it works. On most
compilers I should think it is as efficient too.

Thanks you guys.

Is:
_member.const_iterator it;
legal?

Quote:

The compiler didn't like that line, but it did like:
std::map<std::string, std::string>::const_iterator it;

I'm sure that's what Brian meant to say.

john

Joe Laughlin
Guest

Posted: Fri Oct 22, 2004 8:03 pm Post subject: Re: weird error

Joe Laughlin wrote:

Quote:

(file and class names changed to protect the innocent)

g++ -Wall -c file.cpp: In member function `std::string
Some_Class::get_member(const std::string&) const':
file.cpp:46: passing `const std::map<std::string,
std::string, std::less std::allocator<std::pair std::string> > >' as `this' argument of `_Tp&
std::map<_Key, _Tp, _Compare,
_Alloc>::operator[](const _Key&) [with _Key =
std::string, _Tp = std::string, _Compare =
std::less<std::string>, _Alloc =
std::allocator<std::pair ]' discards qualifiers

I can't make heads or tails of this error. I'm guessing
it has something to do with calling a non-const function
on some const object. Any ideas?

The function SomeClass::get_member is:

std::string SomeClass::get_member(const std::string
&name) const {
return _member[name];
}

where _member is a std::map

Here's another one, probably related to my lack of understanding about the
STL. (These error messages sure aren't very clear!)

Error is:
could not convert `
(&iter)->std::_List_iterator<_Tp, _Ref, _Ptr>::operator*() const [with
_Tp =
SomeClass, _Ref = const SomeClass&, _Ptr = const
SomeClass*]()' to `SomeClass&'

SomeClass is a std::list of a user-defined class.

The error gets raised on the return statement of this function:
SomeClass& AnotherClass::get_element(const string& tag) const
{
std::list<SomeClass>::const_iterator iter = _elements.begin();

// This isn't very well written, and I'm sure there's better
// ways of doing it. Feel free to give me ideas on how to improve it.
while (iter != _elements.end())
{
if (iter->get_member("tag") == tag)
return *iter; // error rasied here
++iter;
}
// throw exception cuz not found
}

Victor Bazarov
Guest

Posted: Fri Oct 22, 2004 8:21 pm Post subject: Re: weird error

Joe Laughlin wrote:

Quote:

Joe Laughlin wrote:

(file and class names changed to protect the innocent)

g++ -Wall -c file.cpp: In member function `std::string
Some_Class::get_member(const std::string&) const':
file.cpp:46: passing `const std::map<std::string,
std::string, std::less std::allocator<std::pair std::string> > >' as `this' argument of `_Tp&
std::map<_Key, _Tp, _Compare,
_Alloc>::operator[](const _Key&) [with _Key =
std::string, _Tp = std::string, _Compare =
std::less<std::string>, _Alloc =
std::allocator<std::pair
]' discards qualifiers

I can't make heads or tails of this error. I'm guessing
it has something to do with calling a non-const function
on some const object. Any ideas?

The function SomeClass::get_member is:

std::string SomeClass::get_member(const std::string
&name) const {
return _member[name];
}

where _member is a std::map

Here's another one, probably related to my lack of understanding about the
STL. (These error messages sure aren't very clear!)

Error is:
could not convert `
(&iter)->std::_List_iterator<_Tp, _Ref, _Ptr>::operator*() const [with
_Tp =
SomeClass, _Ref = const SomeClass&, _Ptr = const
SomeClass*]()' to `SomeClass&'

SomeClass is a std::list of a user-defined class.

The error gets raised on the return statement of this function:
SomeClass& AnotherClass::get_element(const string& tag) const
{
std::list<SomeClass>::const_iterator iter = _elements.begin();

// This isn't very well written, and I'm sure there's better
// ways of doing it. Feel free to give me ideas on how to improve it.
while (iter != _elements.end())
{
if (iter->get_member("tag") == tag)
return *iter; // error rasied here
++iter;
}
// throw exception cuz not found
}

Your 'const' is all screwed up again. The return value of this function
is 'SomeClass&', a reference to non-const SomeClass object. The 'iter'
is declared as 'const_iterator', whose operator* (dereference operator)
yields a 'SomeClass const&', a reference to a const SomeClass object.
Of course it cannot convert a const ref to a non-const ref.

Victor

Joe Laughlin
Guest

Posted: Fri Oct 22, 2004 9:00 pm Post subject: Re: weird error

Victor Bazarov wrote:

Quote:

Joe Laughlin wrote:
Joe Laughlin wrote:

(file and class names changed to protect the innocent)

g++ -Wall -c file.cpp: In member function `std::string
Some_Class::get_member(const std::string&) const':
file.cpp:46: passing `const std::map<std::string,
std::string, std::less std::allocator<std::pair std::string> > >' as `this' argument of `_Tp&
std::map<_Key, _Tp, _Compare,
_Alloc>::operator[](const _Key&) [with _Key =
std::string, _Tp = std::string, _Compare =
std::less<std::string>, _Alloc =
std::allocator<std::pair
]' discards qualifiers

I can't make heads or tails of this error. I'm guessing
it has something to do with calling a non-const function
on some const object. Any ideas?

The function SomeClass::get_member is:

std::string SomeClass::get_member(const std::string
&name) const {
return _member[name];
}

where _member is a std::map

Here's another one, probably related to my lack of
understanding about the STL. (These error messages sure
aren't very clear!)

Error is:
could not convert `
(&iter)->std::_List_iterator<_Tp, _Ref,
_Ptr>::operator*() const [with _Tp =
SomeClass, _Ref = const SomeClass&, _Ptr = const
SomeClass*]()' to `SomeClass&'

SomeClass is a std::list of a user-defined class.

The error gets raised on the return statement of this
function: SomeClass& AnotherClass::get_element(const
string& tag) const {
std::list<SomeClass>::const_iterator iter =
_elements.begin();

// This isn't very well written, and I'm sure
there's better // ways of doing it. Feel free to
give me ideas on how to improve it. while (iter !=
_elements.end()) {
if (iter->get_member("tag") == tag)
return *iter; // error rasied here
++iter;
}
// throw exception cuz not found
}

Your 'const' is all screwed up again. The return value
of this function is 'SomeClass&', a reference to
non-const SomeClass object. The 'iter' is declared as
'const_iterator', whose operator* (dereference operator)
yields a 'SomeClass const&', a reference to a const
SomeClass object. Of course it cannot convert a const ref
to a non-const ref.

Victor

Ah, I understand. So what's the correct thing to do here? (Can I return a
const reference?)

Victor Bazarov
Guest

Posted: Fri Oct 22, 2004 9:48 pm Post subject: Re: weird error

Joe Laughlin wrote:

Quote:

Victor Bazarov wrote:

Joe Laughlin wrote:

Joe Laughlin wrote:

(file and class names changed to protect the innocent)

g++ -Wall -c file.cpp: In member function `std::string
Some_Class::get_member(const std::string&) const':
file.cpp:46: passing `const std::map<std::string,
std::string, std::less std::allocator<std::pair std::string> > >' as `this' argument of `_Tp&
std::map<_Key, _Tp, _Compare,
_Alloc>::operator[](const _Key&) [with _Key =
std::string, _Tp = std::string, _Compare =
std::less<std::string>, _Alloc =
std::allocator<std::pair
]' discards qualifiers

I can't make heads or tails of this error. I'm guessing
it has something to do with calling a non-const function
on some const object. Any ideas?

The function SomeClass::get_member is:

std::string SomeClass::get_member(const std::string
&name) const {
return _member[name];
}

where _member is a std::map

Here's another one, probably related to my lack of
understanding about the STL. (These error messages sure
aren't very clear!)

Error is:
could not convert `
(&iter)->std::_List_iterator<_Tp, _Ref,
_Ptr>::operator*() const [with _Tp =
SomeClass, _Ref = const SomeClass&, _Ptr = const
SomeClass*]()' to `SomeClass&'

SomeClass is a std::list of a user-defined class.

The error gets raised on the return statement of this
function: SomeClass& AnotherClass::get_element(const
string& tag) const {
std::list<SomeClass>::const_iterator iter =
_elements.begin();

// This isn't very well written, and I'm sure
there's better // ways of doing it. Feel free to
give me ideas on how to improve it. while (iter !=
_elements.end()) {
if (iter->get_member("tag") == tag)
return *iter; // error rasied here
++iter;
}
// throw exception cuz not found
}

Your 'const' is all screwed up again. The return value
of this function is 'SomeClass&', a reference to
non-const SomeClass object. The 'iter' is declared as
'const_iterator', whose operator* (dereference operator)
yields a 'SomeClass const&', a reference to a const
SomeClass object. Of course it cannot convert a const ref
to a non-const ref.

Victor

Ah, I understand. So what's the correct thing to do here? (Can I return a
const reference?)

You can of course. I don't know if your algorithm allows you to, though.
Why did you need a non-const ref before?

V

Mike Wahler
Guest

Posted: Fri Oct 22, 2004 9:49 pm Post subject: Re: weird error

"Joe Laughlin" <Joseph.V.Laughlin (AT) boeing (DOT) com> wrote

Quote:

Victor Bazarov wrote:
Your 'const' is all screwed up again. The return value
of this function is 'SomeClass&', a reference to
non-const SomeClass object. The 'iter' is declared as
'const_iterator', whose operator* (dereference operator)
yields a 'SomeClass const&', a reference to a const
SomeClass object. Of course it cannot convert a const ref
to a non-const ref.

Victor

Ah, I understand. So what's the correct thing to do here?

return a const reference.

Quote:

(Can I return a
const reference?)

:-)

-Mike

Joe Laughlin
Guest

Posted: Fri Oct 22, 2004 11:14 pm Post subject: Re: weird error

Joe Laughlin wrote:

Quote:

These weird errors just keep on coming! Thanks everyone again for your
help.

Please don't tell me this error is because of const again... Sad

But I'd
wager it is.

// 6-9 from Accelerated C++
// Use library algorithm to cat all elements of a vector<string>

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>

int main()
{
std::vector<std::string> vec;
vec.push_back("Hi!");
vec.push_back(" How ");
vec.push_back("are ");
vec.push_back("you ");
vec.push_back("doing?");

std::string new_string;

copy(vec.begin(), vec.end(), std::back_inserter(new_string));

std::cout << new_string << std::endl;

return 0;
}

g++ -Wall -pedantic -o 6-9 6-9.cpp
/usr/include/c++/3.2.2/bits/stl_algobase.h: In function `_OutputIter
std::__copy(_RandomAccessIter, _RandomAccessIter, _OutputIter,
std::random_access_iterator_tag) [with _RandomAccessIter = std::string*,
_OutputIter = std::back_insert_iterator /usr/include/c++/3.2.2/bits/stl_algobase.h:260: instantiated from
`_OutputIter std::__copy_aux2(_InputIter, _InputIter, _
OutputIter, __false_type) [with _InputIter = std::string*, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:303: instantiated from
`_OutputIter std::__copy_ni2(_InputIter, _InputIter, _O
utputIter, __false_type) [with _InputIter = std::string*, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:314: instantiated from
`_OutputIter std::__copy_ni1(_InputIter, _InputIter, _O
utputIter, __true_type) [with _InputIter =
__gnu_cxx::__normal_iterator<std::string*, std::vector std::allocat
or >, _OutputIter = std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:349: instantiated from
`_OutputIter std::copy(_InputIter, _InputIter, _OutputI
ter) [with _InputIter = __gnu_cxx::__normal_iterator<std::string*,
std::vector >
, _OutputIter = std::back_insert_iterator<std::string>]'
6-9.cpp:22: instantiated from here
/usr/include/c++/3.2.2/bits/stl_algobase.h:241: no match for `
std::back_insert_iterator<std::string>& = std::basic_string<char,
std::char_traits&' operator
/usr/include/c++/3.2.2/bits/stl_iterator.h:355: candidates are:
std::back_insert_iterator<_Container>&

std::back_insert_iterator<_Container>::operator=(_Container::const_reference
)
[with _Container = std::string]
/usr/include/c++/3.2.2/bits/stl_iterator.h:330:
std::back_insert_iterator<std::string>&
std::back_insert_iterator<std::string>::operator=(const
std::back_insert_iterator<std::string>&)

Mike Wahler
Guest

Posted: Sat Oct 23, 2004 12:03 am Post subject: Re: weird error

"Joe Laughlin" <Joseph.V.Laughlin (AT) boeing (DOT) com> wrote

Quote:

Joe Laughlin wrote:

These weird errors just keep on coming! Thanks everyone again for your
help.

Please don't tell me this error is because of const again... Sad

But I'd
wager it is.

Not this time. Smile

See below.

Quote:

// 6-9 from Accelerated C++
// Use library algorithm to cat all elements of a vector<string

#include #include #include #include #include
int main()
{
std::vector vec.push_back("Hi!");
vec.push_back(" How ");
vec.push_back("are ");
vec.push_back("you ");
vec.push_back("doing?");

std::string new_string;

copy(vec.begin(), vec.end(), std::back_inserter(new_string));

std::cout << new_string << std::endl;

return 0;
}

g++ -Wall -pedantic -o 6-9 6-9.cpp
/usr/include/c++/3.2.2/bits/stl_algobase.h: In function `_OutputIter
std::__copy(_RandomAccessIter, _RandomAccessIter, _OutputIter,
std::random_access_iterator_tag) [with _RandomAccessIter =
std::string*,
_OutputIter = std::back_insert_iterator /usr/include/c++/3.2.2/bits/stl_algobase.h:260: instantiated from
`_OutputIter std::__copy_aux2(_InputIter, _InputIter, _
OutputIter, __false_type) [with _InputIter = std::string*, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:303: instantiated from
`_OutputIter std::__copy_ni2(_InputIter, _InputIter, _O
utputIter, __false_type) [with _InputIter = std::string*, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:314: instantiated from
`_OutputIter std::__copy_ni1(_InputIter, _InputIter, _O
utputIter, __true_type) [with _InputIter =
__gnu_cxx::__normal_iterator<std::string*, std::vector std::allocat
or >, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:349: instantiated from
`_OutputIter std::copy(_InputIter, _InputIter, _OutputI
ter) [with _InputIter = __gnu_cxx::__normal_iterator<std::string*,
std::vector , _OutputIter = std::back_insert_iterator 6-9.cpp:22: instantiated from here
/usr/include/c++/3.2.2/bits/stl_algobase.h:241: no match for `
std::back_insert_iterator<std::string>& = std::basic_string<char,
std::char_traits&' operator
/usr/include/c++/3.2.2/bits/stl_iterator.h:355: candidates are:
std::back_insert_iterator<_Container>&

std::back_insert_iterator<_Container>::operator=(_Container::const_reference
)
[with _Container = std::string]
/usr/include/c++/3.2.2/bits/stl_iterator.h:330:
std::back_insert_iterator<std::string>&
std::back_insert_iterator<std::string>::operator=(const
std::back_insert_iterator<std::string>&)

'back_insert_iterator' requires that the container type specified by
its template argument defines members 'push_back()' and 'value_type'.
'std::string' defines the latter, but not the former.

IOW you cannot use 'back_insert_iterator' with a 'std::string'.
('std::string', while sharing much commonality with them, isn't
strictly a 'container').

-Mike

Joe Laughlin
Guest

Posted: Sat Oct 23, 2004 1:04 am Post subject: Re: weird error

Mike Wahler wrote:

Quote:

"Joe Laughlin" <Joseph.V.Laughlin (AT) boeing (DOT) com> wrote in
message news:I60Dvs.FqL (AT) news (DOT) boeing.com...
Joe Laughlin wrote:

These weird errors just keep on coming! Thanks everyone
again for your help.

Please don't tell me this error is because of const
again... Sad

But I'd wager it is.

Not this time. Smile

See below.

// 6-9 from Accelerated C++
// Use library algorithm to cat all elements of a
vector<string

#include #include #include #include #include
int main()
{
std::vector vec.push_back("Hi!");
vec.push_back(" How ");
vec.push_back("are ");
vec.push_back("you ");
vec.push_back("doing?");

std::string new_string;

copy(vec.begin(), vec.end(),
std::back_inserter(new_string));

std::cout << new_string << std::endl;

return 0;
}

g++ -Wall -pedantic -o 6-9 6-9.cpp
/usr/include/c++/3.2.2/bits/stl_algobase.h: In function
`_OutputIter std::__copy(_RandomAccessIter,
_RandomAccessIter, _OutputIter,
std::random_access_iterator_tag) [with
_RandomAccessIter = std::string*, _OutputIter =
std::back_insert_iterator /usr/include/c++/3.2.2/bits/stl_algobase.h:260:
instantiated from `_OutputIter
std::__copy_aux2(_InputIter, _InputIter, _
OutputIter, __false_type) [with _InputIter =
std::string*, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:303:
instantiated from `_OutputIter
std::__copy_ni2(_InputIter, _InputIter, _O
utputIter, __false_type) [with _InputIter =
std::string*, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:314:
instantiated from `_OutputIter
std::__copy_ni1(_InputIter, _InputIter, _O
utputIter, __true_type) [with _InputIter =
__gnu_cxx::__normal_iterator<std::string*,
std::vector or >, _OutputIter =
std::back_insert_iterator<std::string>]'
/usr/include/c++/3.2.2/bits/stl_algobase.h:349:
instantiated from `_OutputIter std::copy(_InputIter,
_InputIter, _OutputI
ter) [with _InputIter =
__gnu_cxx::__normal_iterator<std::string*,
std::vector , _OutputIter = std::back_insert_iterator 6-9.cpp:22: instantiated from here
/usr/include/c++/3.2.2/bits/stl_algobase.h:241: no
match for ` std::back_insert_iterator<std::string>& =
std::basic_string<char, std::char_traits std::allocator<char> >&' operator
/usr/include/c++/3.2.2/bits/stl_iterator.h:355:
candidates are: std::back_insert_iterator<_Container>&

std::back_insert_iterator<_Container>::operator=(_Container::const_reference
)
[with _Container = std::string]
/usr/include/c++/3.2.2/bits/stl_iterator.h:330:
std::back_insert_iterator<std::string>&

std::back_insert_iterator<std::string>::operator=(const
std::back_insert_iterator<std::string>&)

'back_insert_iterator' requires that the container type
specified by its template argument defines members
'push_back()' and 'value_type'. 'std::string' defines the
latter, but not the former.

IOW you cannot use 'back_insert_iterator' with a
'std::string'. ('std::string', while sharing much
commonality with them, isn't strictly a 'container').

-Mike

Argh.

From "Accelerated C++", pg 121:

"back_inserter(c)
Yields an iterator on the container c that appends elements to c. The
container must support push_back, which the list, vector, and the string
types all do."

Joe Laughlin
Guest

Posted: Mon Oct 25, 2004 7:13 pm Post subject: Re: weird error

Joe Laughlin wrote:

Quote:

Mike Wahler wrote:
"Joe Laughlin" <Joseph.V.Laughlin (AT) boeing (DOT) com> wrote in
message news:I60Dvs.FqL (AT) news (DOT) boeing.com...
Joe Laughlin wrote:

These weird errors just keep on coming! Thanks everyone
again for your help.

Please don't tell me this error is because of const
again... Sad

But I'd wager it is.

Not this time. Smile

So, was the book correct? Or wrong?

Mike Wahler
Guest

Posted: Tue Oct 26, 2004 5:20 pm Post subject: Re: weird error

"Joe Laughlin" <Joseph.V.Laughlin (AT) boeing (DOT) com> wrote

Quote:

Joe Laughlin wrote:

From "Accelerated C++", pg 121:

"back_inserter(c)
Yields an iterator on the container c that appends
elements to c. The container must support push_back,
which the list, vector, and the string types all do."

So, was the book correct? Or wrong?

I think it's wrong. As far as I can tell from the standard,
'std::basic_string<>' is not required to provide 'push_back()',
but neither is it prohibited from doing so.

Of course I invite anyone else to give their interpretation,
so we can know for sure.

I scanned the AC++ errata pages, but I don't see this issue
mentioned.

Anyone else?

-Mike

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