Help with map iterator

[Bill Oliver]

Help! I am writing an image processing package. For
one constructor, I allow creating an image from a
map of points and color values. The points are
of a "position" class and the colors are just a
vector. It starts thusly:

template <class T>
image<T>::image(map<position<int, vector<T >& in_map){

cerr<< "***** ***** ***** ***** ***** *****\n";
cerr<< "making image from map \n";
cerr<< "***** ***** ***** ***** ***** *****\n";

// make an iterator into the input map
map< position<int>, vector<T::iterator mapit;
mapit = in_map.begin();
.... do stuff with the iterator

}
Oddly, this compiled just fine a month or so ago before I
upgraded my OS from Mandriva 2006 to Mandriva 2007.

Now, however, I get the error:

constructors.cpp: In constructor 'image<T>::image(std::map<position<int>, std::vector<T, std::allocator<_CharT, std::less<position<int, std::allocator<std::pair<const position<int>, std::vector<T, std::allocator<_CharT >&)':
constructors.cpp:127: error: expected `;' before 'mapit'
constructors.cpp:128: error: 'mapit' was not declared in this scope

Even more oddly, to me, if I add another iterator, I don't get
an additional error:
template <class T>
image<T>::image(map<position<int, vector<T >& in_map){

cerr<< "***** ***** ***** ***** ***** *****\n";
cerr<< "making image from map \n";
cerr<< "***** ***** ***** ***** ***** *****\n";

// make an iterator into the input map
map<char,int>::iterator testiterator;
map< position<int>, vector<T::iterator mapit;
mapit = in_map.begin();
.... do stuff with the iterator

}

gives the same error -- it doesn't choke on testiterator.

Configuration:

HP Pavilion zd8000 Pentium4 laptop
Mandriva 2007 linux
gcc version 4.1.1 20060724 (prerelease) (4.1.1-3mdk)
Any pointers would be appreciated!!

Thanks,

billo

[Gianni Mariani]

Bill Oliver wrote:

Help! I am writing an image processing package. For
one constructor, I allow creating an image from a
map of points and color values. The points are
of a "position" class and the colors are just a
vector. It starts thusly:

template <class T>
image<T>::image(map<position<int, vector<T >& in_map){

cerr<< "***** ***** ***** ***** ***** *****\n";
cerr<< "making image from map \n";
cerr<< "***** ***** ***** ***** ***** *****\n";

// make an iterator into the input map
map< position<int>, vector<T::iterator mapit;

replace the line above with:

typename map< position<int>, vector<T::iterator mapit;

mapit = in_map.begin();

....

Any pointers would be appreciated!!

Types from dependant classes need a "typename" specifier.

[Bill Oliver]

In article <12*************@corp.supernews.com>,
Bill Oliver <bi***@radix.netwrote:

>
Help! I am writing an image processing package..

Here's some further data. The error goes away, and
the program runs fine if I replace:

map<position<int>,vector<T::iterator mapit;

with

map<position<int>,vector<float::iterator mapit;
even though T is set to float in the calling routine.
billo

[Bill Oliver]

In article <45**********************@per-qv1-newsreader-01.iinet.net.au>,
Gianni Mariani <gi*******@mariani.wswrote:

>
Types from dependant classes need a "typename" specifier.

Thank you!!!! That was exactly the problem. Doh.

Now I am wondering why it *used* to work OK.

billo

[Kai-Uwe Bux]

Bill Oliver wrote:

>
Help! I am writing an image processing package. For
one constructor, I allow creating an image from a
map of points and color values. The points are
of a "position" class and the colors are just a
vector. It starts thusly:

template <class T>
image<T>::image(map<position<int, vector<T >& in_map){

cerr<< "***** ***** ***** ***** ***** *****\n";
cerr<< "making image from map \n";
cerr<< "***** ***** ***** ***** ***** *****\n";

// make an iterator into the input map
map< position<int>, vector<T::iterator mapit;

typename map< position<int>, vector<T::iterator mapit;

mapit = in_map.begin();
.... do stuff with the iterator

}
Oddly, this compiled just fine a month or so ago before I
upgraded my OS from Mandriva 2006 to Mandriva 2007.

Now, however, I get the error:

constructors.cpp: In constructor 'image<T>::image(std::map<position<int>,
std::vector<T, std::allocator<_CharT, std::less<position<int,
std::allocator<std::pair<const position<int>, std::vector<T,
std::allocator<_CharT >&)': constructors.cpp:127: error: expected
`;' before 'mapit' constructors.cpp:128: error: 'mapit' was not declared
in this scope

Even more oddly, to me, if I add another iterator, I don't get
an additional error:
template <class T>
image<T>::image(map<position<int, vector<T >& in_map){

cerr<< "***** ***** ***** ***** ***** *****\n";
cerr<< "making image from map \n";
cerr<< "***** ***** ***** ***** ***** *****\n";

// make an iterator into the input map
map<char,int>::iterator testiterator;
map< position<int>, vector<T::iterator mapit;
mapit = in_map.begin();
.... do stuff with the iterator

}

gives the same error -- it doesn't choke on testiterator.

You only need the typename keyword for dependent names. Since
map<char,int>::iterator does not involve the template paramenter T, it is
not a dependent name, hence no "typename" is needed.
Best

Kai-Uwe Bux

[Kai-Uwe Bux]

Bill Oliver wrote:

In article <45**********************@per-qv1-newsreader-01.iinet.net.au>,
Gianni Mariani <gi*******@mariani.wswrote:

>>
Types from dependant classes need a "typename" specifier.

Thank you!!!! That was exactly the problem. Doh.

Now I am wondering why it *used* to work OK.

I bet, you upgraded you g++.
Best

Kai-Uwe Bux