C ++列表迭代器不兼容

Question

This is the code that I have in my main.cpp

std::list<AbstractBlock*>::iterator i;

    for (i = universe.getLoadedBlocks().begin(); i != universe.getLoadedBlocks().end(); i++){
        window.draw((*i)->draw());

    }

Universe.cpp:

std::list<AbstractBlock*> Universe::getLoadedBlocks(){
    return chunkManager->getLoadedBlocks();
}

CunkManager.cpp:

std::list<AbstractBlock*> ChunkManager::getLoadedBlocks(){
    return loadedBlocks;
}

And loadedBlocks is an std::list<AbstractBlock*>

I'm experimenting with lists and trying them out for the first time... I'm not sure why I'm getting this error

Answer 1

std::list<AbstractBlock*> Universe::getLoadedBlocks() { ... }
^^^^^^^^^^^^^^^^^^^^^^^^^ // This returns a copy of the list

Therefore, universe.getLoadedBlocks().begin() uses one copy of the list and universe.getLoadedBlocks().end() uses a different copy of the list. This is why the iterators are incompatible (ie, they are from different lists).

Said another way, the begin iterator of one list instance will never be equal to the end iterator from a different list instance.

If you don't change the getLoadedBlocks() function you could try:

std::list<AbstractBlock*> values = universe.getLoadedBlocks();
for (i = values.begin(); i != values.end(); i++) // Note: You should use ++i here (for possible efficiency benefits)
{
    window.draw((*i)->draw());
}

Edit

As Jarod42 points out you could also use the more convenient/succinct range-based for loop, assuming you're using a C++11 compatible compiler.

for (auto& block : universe.getLoadedBlocks())
{
    window.draw(block->draw());
}