Hi, On Monday, 10. October 2011 11:04:38 Christoph wrote:
[...]
You need to use boost::tie if your iterator types are not already in the boost namespace. The definition of tie is in Boost.Tuple, I think.
Thank you Jeremiah for pointing that out. I think i still have my problems with ADL and name spaces... Off course ADL (Argument Dependant Name Lookup) will not find any definition for 'tie' with the arguments being in the name space 'std', because 'tie' is defined in the name space 'boost' and not in the name space 'std'.
So here is an unhappy example in which i write 'boost::tie' in stead of just 'tie' which compiles without errors but does not do what i expected:
// begin code
#include <iostream> #include <boost/graph/adjacency_list.hpp>
typedef boost::adjacency_list < boost::listS, boost::vecS, boost::bidirectionalS> my_graph;
typedef boost::graph_traits <my_graph> my_graph_traits;
template <typename T> boost::tuple < typename T::iterator, typename T::iterator> elements (T container)
Please note that you are using a _copy_ here and thus you also return the iterators of a _copy_ but not of the "original" container. Therefore, I assume that the iterators returned are not valid and might even lead to a segmentation fault (as they do on my machine, since this container-copy is only valid during the execution of elements() ). Perhaps you want to try "const T& container" in the argument list. When I use that, I get: 1: loop in elements() 2: loop in elements() 3: loop in elements() 4: loop in elements() 1, i = 0 2, i = 1 3, i = 2 4, i = 3 1, i = 4 2, i = 5 3, i = 6 4, i = 7
{ typename T::iterator beg = container.begin(); typename T::iterator end = container.end(); for (;beg != end; ++beg) std::cout << *beg << ": loop in elements()" << std::endl; return boost::make_tuple(container.begin(), container.end()); }
int main () { std::list <int> list; list.push_back(1);list.push_back(2); list.push_back(3);list.push_back(4);
std::list <int>::iterator beg, end; int i = 0;
/* uncomment for testing purpose for (boost::tie(beg, end) = elements <std::list<int> >(list); beg != end; ++beg) { std::cout << *beg << ", i = " << i++ << std::endl; }*/
beg = list.begin(); end = list.end(); for(; beg != end; ++beg) std::cout << *beg << ", i = " << i++ << std::endl; return 0; } // end code
If you compile and run the code as it is the output is: 1, i = 0 2, i = 1 3, i = 2 4, i = 3
However if you uncomment the 'for-loop' part and leave the rest of the code as it is, compile and run, than the output will be: 1: loop in elements() 2: loop in elements() 3: loop in elements() 4: loop in elements() 1, i = 0
I expected the output to be:
1: loop in elements() 2: loop in elements() 3: loop in elements() 4: loop in elements() 1, i = 0 2, i = 1 3, i = 2 4, i = 3 1, i = 0 2, i = 1 3, i = 2 4, i = 3
I do not get it. Maybe you could help me to find out.
Best, Cedric
best regards again Christoph
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