Question

I’m trying to run this function:

os::TMXTileset* os::TMXMap::getTilesetFromGid(int gid)
    {
        TMXTileset* tileset;
        std::map<std::string, TMXTileset>::iterator it;
        std::map<std::string, TMXTileset>::iterator comp;

        for (it=tilesetMap.begin(); it != tilesetMap.end(); it++)
        {
            comp = it;
            comp++;
            if ((gid >= it->second.getFirstGid()) && (gid < comp->second.getFirstGid()))
            {
                return &it->second;
            }
        }
        tileset = &it->second;
        return tileset;
    }

..but it is giving me this error:

“map/set iterator not derefrencable”

My first thought was to stop dereferencing it (using it->second instead of (*it).second), but that didn’t change anything at all.

Any ideas?

Answer 1

you first copy it, then you advance the copy and then you dereference the copy. This means you dereference end() whenever it is on the element before the last element.

You can easily test this on a map with 1 entry only – it should always fail to dereference comp.

you should do something like:

TMXTileset* tileset;
std::map<std::string, TMXTileset>::iterator it;
std::map<std::string, TMXTileset>::iterator comp;

for (it=tilesetMap.begin(); /*it != tilesetMap.end() can be ommited due to check for comp */; it++)
{
    comp = it;
    comp++;
    if (comp == tilesetMap.end())
    {
       break;
    }
    ...
}