Strange Error with Vectors in C++ - c++

Question

Every time I compile the code for a RTS Project I am working on, I get this error:
error C2664: 'std::_Vector_iterator<_Ty,_Alloc> std::vector<_Ty>::erase(std::_Vector_const_iterator<_Ty,_Alloc>)' : cannot convert parameter 1 from 'MAPTILE *' to 'std::_Vector_const_iterator<_Ty,_Alloc>'
The code area that I have for this method is this:
MAPTILE *startTile = GetTile(start);
MAPTILE *goalTile = GetTile(goal);
...
std::vector<MAPTILE*> open; //Create Our Open list
startTile->g = 0; //Init our starting point (SP)
startTile->f = H(start, goal);
startTile->open = true;
open.push_back(startTile); //Add SP to the Open list
bool found = false; // Search as long as a path hasnt been found,
while(!found && !open.empty()) // or there is no more tiles to search
{
MAPTILE * best = open[0]; // Find the best tile (i.e. the lowest F value)
int bestPlace = 0;
for(int i=1;i<open.size();i++)
if(open[i]->f < best->f)
{
best = open[i];
bestPlace = i;
}
if(best == NULL)break; //No path found
open[bestPlace]->open = false;
open.erase(&open[bestPlace]); // Take the best node out of the Open list
I have searched on this website and a few others, but I could not find the correct area.
I am reading "Programming a RTS Game With Direct3D" By Carl Granberg.
All of my code is right because I matched it with the source code, and I got the same error.
I am using Visual C++ 2008 Express Edition.
I have never gotten this error before.

Answer 1

erase wants an iterator and you are giving it a pointer to an element within the array. Use std::advance or keep a handle to an iterator.
std::vector<MAPTILE*> p = open.begin();
std::advance(p, bestPlace);
open.erase(p);
EDIT I forgot that std::advance doesn't return anything. Sorry about that. I haven't done serious C++ development for about five years.
I would rewrite your for loop to use iterators instead of indexes.
I believe that the following snippet is equivalent to your snippet after replacing the array indexing with iterators. I had to add the typedef to make it more readable.
MAPTILE *startTile = GetTile(0);
startTile->g = 0;
startTile->f = H(0, 10);
startTile->open = true;
std::vector<MAPTILE*> open;
open.push_back(startTile);
typedef std::vector<MAPTILE*>::iterator Iterator;
bool found = false;
while (!found && !open.empty()) {
Iterator best = open.begin();
for (Iterator iter=best+1, end=open.end();
iter!=end; ++iter)
{
if ((*iter)->f < (*best)->f) {
best = iter;
}
}
if (*best == NULL) {
break;
}
(*best)->open = false;
open.erase(best);
}
I'm not completely convinced that the if (*best == NULL) condition will ever be matched though. This compiles without error under clang++ (sorry, no visual studio in my house). When I run your snippet through clang++, I get comparable failures to yours:
foo.cpp:85:14: error: calling a private constructor of class
'std::__1::__wrap_iter<MAPTILE *const *>'
open.erase(&open[bestPlace]);
^
/Library/Developer/CommandLineTools/usr/include/c++/v1/iterator:1381:31: note:
declared private here
_LIBCPP_INLINE_VISIBILITY __wrap_iter(iterator_type __x) _NOEXCEPT_D...
^
1 error generated.
I don't know what else to say, std::vector<>::erase takes a std::vector<>::iterator parameter and that's all that there is to it. My guess is that the book was written against a version of VC++ that used pointers for vector iterators though I don't recall one that ever did that.