C++ priority_queue with lambda comparator error

Question

I have the following erroneous code which I am trying to compile in VC2010, but I\'m getting the error C2974 this only occurs when I include the lambda expression, so I\'m g

Answer 1

priority_queue takes the comparator as a template argument. Lambda functions are objects, and thus can't be used as template arguments (only very few types can be, among them integral types).

You can try using decltype there:

priority_queue< adjlist_edge , vector,
               decltype( [](adjlist_edge a, adjlist_edge b) -> bool {
                if(a.second > b.second){ return true; } else { return false; }
               })>
adjlist_pq( [](adjlist_edge a, adjlist_edge b) -> bool {
                if(a.second > b.second){ return true; } else { return false; }
             } );

Failing that (and it will), you can use function<>:

priority_queue< adjlist_edge , vector,
                function >
adjlist_pq( [](adjlist_edge a, adjlist_edge b) -> bool {
                if(a.second > b.second){ return true; } else { return false; }
            } );