deleting the contents of a std::map
Author
Hello!
Nice xmas theme.....
I have a puzzle over the best way to delete the contents of a std::map, in MSVC2003
Using a std::vector, I normally iterate thru the vector, SAFE_DELETEing, then do a .clear();
I tried this:
std::map< int, cProxyObject*, std::less<int> >::iterator iter;
for ( iter = m_objectList.begin(); iter != m_objectList.end(); ++iter )
delete *iter;
m_objectList.clear();
but it doesnt like the delete *iter; line.
Any suggestions gratefully appreciated!
Si
Haven't messed with C++ in a while, but...
the pointer is sitting at the value portion in the map. so you would want to do
delete iter->second
the pointer is sitting at the value portion in the map. so you would want to do
delete iter->second
Of course you can save yourself some headaches by using a map of smart pointers or possibly boost::ptr_map.
Author
Following up on this subject, I have now come across a further problem. Here's my code:
for ( iter = m_objectList.begin(); iter != m_objectList.end(); ++iter )
{
SAFE_DELETE( iter->second );
//m_objectList.erase( iter );
g_log->Log( L"%d objects remaining\n", m_objectList.size() );
}
This is a puzzle. The code successfully deletes all the objects stored in iter->second, but the m_objectList still contains NULLed entries.
Okay, so by uncommenting the above line, the m_objectList.size() reflects only the undeleted objects. Seems greats but......
Unfortunately, by using .erase() I seem to be mucking up the iterator loop. How can I loop though something which I am deleting!!!
I tried:
m_objectList.erase( iter->first );
but same results.
Thanks in advance
Simon
for ( iter = m_objectList.begin(); iter != m_objectList.end(); ++iter )
{
SAFE_DELETE( iter->second );
//m_objectList.erase( iter );
g_log->Log( L"%d objects remaining\n", m_objectList.size() );
}
This is a puzzle. The code successfully deletes all the objects stored in iter->second, but the m_objectList still contains NULLed entries.
Okay, so by uncommenting the above line, the m_objectList.size() reflects only the undeleted objects. Seems greats but......
Unfortunately, by using .erase() I seem to be mucking up the iterator loop. How can I loop though something which I am deleting!!!
I tried:
m_objectList.erase( iter->first );
but same results.
Thanks in advance
Simon
Quote:Original post by sipickles
Unfortunately, by using .erase() I seem to be mucking up the iterator loop. How can I loop though something which I am deleting!!!
This just came up here, but it was for a list, so for a map, it's still the same logics [wink]
iter = m_objectList.begin();while(iter != m_objectList.end()){ SAFE_DELETE( iter->second ); m_objectList.erase( iter ); g_log->Log( L"%d objects remaining\n", m_objectList.size() ); iter = m_objectList.begin();}That's it! Of course if you look further down the page on that last link, SiCrane suggests just calling clear at the end rather than try to delete as you go - which is the best thing to do, unless you are not erasing all the tiems in the map. For example, you would want to use my code if you had:
iter = m_objectList.begin();while(iter != m_objectList.end()){ SAFE_DELETE( iter->second ); m_objectList.erase( iter ); g_log->Log( L"%d objects remaining\n", m_objectList.size() ); if(objectList.size() % 2 == 0) break; iter = m_objectList.begin();}In which case, you definitly don't want to call clear at the end. [wink]
If you are going to erase as you go you might as well do:
As Drew says above, it would probably be faster to delete them and then clear at the end. I haven't looked at how they code clear() but hopefully it isn't by iteratoring through each one and deleting them one at a time (while relinking everything)
while (!m_objectList.empty()){ SAFE_DELETE(m_objectList->begin()->second); m_objectList.erase(m_objectList.begin()); g_log->Log( L"%d objects remaining\n", m_objectList.size() );}As Drew says above, it would probably be faster to delete them and then clear at the end. I haven't looked at how they code clear() but hopefully it isn't by iteratoring through each one and deleting them one at a time (while relinking everything)
But what if you only want to delete some of them?
[edit - add code for delete_if_we_should. :P]
[edit - add code for delete_if_we_should. :P]
bool delete_if_we_should(iterator I){ if (some_test_involving_I) { delete I->second; return true; } return false;}for (iterator I = container.begin(); I != container.end(); ){ if (delete_if_we_should(I)) I = container.erase(I); else ++I;}Quote:Original post by Deyja
But what if you only want to delete some of them?for (iterator I = container.begin(); I != container.end(); ){ if (delete_if_we_should(I)) I = container.erase(I); else ++I;}
In a map, erase doesn't return an iterator.
for (iterator I = container.begin(); I != container.end(); ){ if (delete_if_we_should(I)) { iterator nextI = I; nextI++; container.erase(I); I = nextI; } else ++I;}Quote:Original post by SiCrane
Of course you can save yourself some headaches by using a map of smart pointers or possibly boost::ptr_map.
You see this post? These are some of the headaches you could have saved.
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