pass a function into a priority queue

[Michael]

#include<queue>
using namespace std;
bool comp(int,int);
priority_queue<int>q(comp);

test.cpp:4: error: no matching function for call to
‘std:riority_queue<int, std::vector<int, std::allocator<int> >,
std::less<int> >:riority_queue(bool (&)(int, int))’
/usr/include/c++/4.3/bits/stl_queue.h:403: note: candidates are:
std:riority_queue<_Tp, _Sequence, _Compare>:riority_queue(const
_Compare&, const _Sequence&) [with _Tp = int, _Sequence = std::vector<int,
std::allocator<int> >, _Compare = std::less<int>]
/usr/include/c++/4.3/bits/stl_queue.h:374: note:
std:riority_queue<int, std::vector<int, std::allocator<int> >,
std::less<int> >:riority_queue(const std:riority_queue<int,
std::vector<int, std::allocator<int> >, std::less<int> >&)

How can I make comp as the comparison function for q?

 

[Alf P. Steinbach]

* Michael:

#include<queue>
using namespace std;
bool comp(int,int);
priority_queue<int>q(comp);

test.cpp:4: error: no matching function for call to
‘std:riority_queue<int, std::vector<int, std::allocator<int> >,
std::less<int> >:riority_queue(bool (&)(int, int))’
/usr/include/c++/4.3/bits/stl_queue.h:403: note: candidates are:
std:riority_queue<_Tp, _Sequence, _Compare>:riority_queue(const
_Compare&, const _Sequence&) [with _Tp = int, _Sequence = std::vector<int,
std::allocator<int> >, _Compare = std::less<int>]
/usr/include/c++/4.3/bits/stl_queue.h:374: note:
std:riority_queue<int, std::vector<int, std::allocator<int> >,
std::less<int> >:riority_queue(const std:riority_queue<int,
std::vector<int, std::allocator<int> >, std::less<int> >&)

How can I make comp as the comparison function for q?

Reading the documentation will help.

Reading the error message above may also help (just read one little bit at a
time, going forward slowly enough that it makes sense) -- what does it say?

If you don't have documentation of the standard library, try downloading the
latest draft of the C++0x standard, and/or visit e.g. Microsoft's MSDN Library
pages and/or Dinkumware's library docs and/or StlLib pages or whatever.


Cheers & hth.,

- Alf

 

[pasa]

#include<queue>
using namespace std;
bool comp(int,int);
priority_queue<int>q(comp);
How can I make comp as the comparison function for q?

http://msdn.microsoft.com/en-us/library/4ef4dae9.aspx
use comp as third parameter of the template

 

[James Kanze]

http://msdn.microsoft.com/en-us/library/4ef4dae9.aspx
use comp as third parameter of the template

The third parameter of the template is a type parameter, and
requires a type. The symbol comp isn't a type. He has to both
specify the correct type "bool (*)( int, int )" as third
argument, and pass the function as argument, e.g.:

priority_queue< int,
std::vector< int >,
bool (*)( int, int ) >
q( &comp ) ;