Iterator Confusion

I'm sure once I see the solution to this problem I'll be banging my head on the desk but anyway, here goes.

I created a std::map that I'm iterating through checking for a value. If the value matches, I delete the entry in map and continue on until I reach the end of the list.

The problem I'm having is when I try to delete the last element in the map. It would make sense that there are no further elements after deleting it. A this point the program backs out with a debug error.

I thought to add a check, if(it = map.end()) but I'm getting " conditional expression of type 'std::_Tree<_Traits>::iterator' is illegal" error. So clearly I'm using it incorrectly.

Here's the block of code that I'm using. The only real relevant part is the for() loop iterating through mTextureArray which is a std::map:

Code:

---

for(map<Image*, pair<GLuint, int> >::iterator i  ; i != mTextureArray.end(); i++)
{
        if((currentTick - i->second.second) > TEXTURE_EXPIRE_TIME)
        {
                glDeleteTextures(1, &i->second.first);
                mTextureArray.erase(i);
        }
}

---

Quote:

---

Originally Posted by leeor_net

I created a std::map that I'm iterating through checking for a value. If the value matches, I delete the entry in map and continue on until I reach the end of the list.

---

Are you sure that a std::map is the correct container for this? Anyway, what you to do is this:

Code:

---

map<Image*, pair<GLuint, int> >::iterator i = mTextureArray.begin();
while(i != mTextureArray.end())
{
    if((currentTick - i->second.second) > TEXTURE_EXPIRE_TIME)
    {
        glDeleteTextures(1, &i->second.first);
        mTextureArray.erase(i++);
    }
    else
    {
        ++i;
    }
}

---

Quote:

---

Originally Posted by laserlight

Are you sure that a std::map is the correct container for this?

---

No, not really. I asked about it yesterday and somebody suggested I use a std:: pair<>. The comparisons work but I don't know if there's a better solution.

This now works as I expect it to. Now I'm interested in why it works like this so I can have a better understanding of how to properly use iterators.

Thanks for the tip. I always appreciate your help!

Quote:

---

Originally Posted by leeor_net

This now works as I expect it to. Now I'm interested in why it works like this so I can have a better understanding of how to properly use iterators.

---

When an element is erased from a std::map, iterators that refer to it are invalidated. Therefore we should advance the iterator before using it to erase the element, and post-increment works just right to do that.

Ah, I understand now. That makes perfect sense. I knew a bit about invalidating iterators but never thought I had come across it.

Thank you!