Re: loop a queue

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Sun, 01 Feb 2009 18:59:55 -0600

Message-ID:

<m1hco4da6v63ndgeoh9h1s638e0nqqjmd9@4ax.com>

On Sun, 01 Feb 2009 16:12:35 -0800, Carl Forsman <fatwallet951@yahoo.com>
wrote:

I have a queue of IDs object <ID, timestamp>

why when I use an iterator to loop through the queue and get each of
the ID inside IDs object.

I got following error?

===========

typedef const char* id_type;
typedef unsigned int timestamp_type;
typedef std::pair<id_type, timestamp_type> entry_type;

std::queue< entry_type > * IDs;

for ( std::queue<entry_type>::const_iterator iter = IDs.begin();
iter != IDs.end(); ++iter )
cout << iter '\n';

===========
error C2039: 'const_iterator' : is not a member of 'std::queue<_Ty>'
1> with
1> [
1> _Ty=entry_type
1> ]
error C2065: 'const_iterator' : undeclared identifier
error C2146: syntax error : missing ';' before identifier 'iter'
error C2065: 'iter' : undeclared identifier
error C2228: left of '.begin' must have class/struct/union
1> type is 'std::queue<_Ty> *'
1> with
1> [
1> _Ty=entry_type
1> ]
1> did you intend to use '->' instead?

As indicated by the error messages, there are two mistakes:

1. std::queue does not define iterator types or support iteration. You can
use deque or even list instead.

2. You're using . where you need to use ->.

In addition, I'm assuming IDs is set to a valid pointer value in code you
didn't show. Finally, due to lifetime issues, it's often an error to store
char* representing strings in a container; it'll work only if the lifetime
of the stored strings exceeds the lifetime of the container. One way to
avoid this problem is to use std::string.

--
Doug Harrison
Visual C++ MVP