Standard Template Library map:find() returns garbage

[cyndykoobs]

I have run into a problem that I cannot seem to figure out regarding a method call to STL map::find(). When the key value can't be found in the map (this is an expected scenario), it returns end() that has _MyValue = unitialized memory (it appears). Thus, the returned iterator is garbage and an exception is thrown eventually. I thought that find() returned the location succeeding the last element in the map if a match was not found. It seems to be returning end(). The map looks like this:

typedef list< CpProts > SRCP_PROTS_LIST;
typedef map< long, SRCP_PROTS_LIST*, CpProtsCmp, CpProtsList2 >    SRCP_PROTS_LISTMAP;

where:
- CpProts is a class containing methods and fields
- class CpProtsCmp : public less< long > {};
- class CpProtsList : public allocator< CpProts > {};
- class CpProtsList2 : public allocator< std::list<CpPro ts,CpProtsList> *> {};

here is the code where the exception occurs:

DWORD imageType = 0x1000007F;
SRCP_PROTS_LISTMAP m_ProtsListMap;
SRCP_PROTS_LISTMAP::iterator listMapIt = m_ProtsListMap.find(imageType);
SRCP_PROTS_LIST* pList = (*listMapIt).second;  <<-- 
 
listMapIt.ptr->second =  0xbaadf00d 

a little complicated but it has worked up until we changed from VS 6.0 to VS 2005 earlier this year. I've inspected the map once all of the values are added and everything looks like I would expect. Using a debug build, I've crawled through the MS code and it seems like the compares (lessthan) are working correctly except in the case where the key cannot be found in the map.

I am using Visual Studio 2005 on Windows XP SP2, Dell 670 workstation. I'm at the end of my rope so I am hopeful that someone out there can see what I can't see.

thanks,
Cyndy

[weaknessforcats]

DWORD imageType = 0x1000007F;
SRCP_PROTS_LIST MAP m_ProtsListMap;
SRCP_PROTS_LIST MAP::iterator listMapIt = m_ProtsListMap. find(imageType) ;
SRCP_PROTS_LIST * pList = (*listMapIt).se cond; <<--

listMapIt.ptr->second = 0xbaadf00d

When the find fails, listMapIt is m_ProtsListMap. end(). That means listMapIt is garbage.

You need to:

DWORD imageType = 0x1000007F;
SRCP_PROTS_LISTMAP m_ProtsListMap;
SRCP_PROTS_LISTMAP::iterator listMapIt = m_ProtsListMap.find(imageType);
SRCP_PROTS_LIST* pList;
 
if (listMapIt != m_ProtsListMap.end())
{
     plist = (*listMapIt).second;  
}
else
{
     //whatever you do when it's not found.
} 
 

[cyndykoobs]

When the find fails, listMapIt is m_ProtsListMap. end(). That means listMapIt is garbage.

You need to:

DWORD imageType = 0x1000007F;
SRCP_PROTS_LISTMAP m_ProtsListMap;
SRCP_PROTS_LISTMAP::iterator listMapIt = m_ProtsListMap.find(imageType);
SRCP_PROTS_LIST* pList;
 
if (listMapIt != m_ProtsListMap.end())
{
     plist = (*listMapIt).second;  
}
else
{
     //whatever you do when it's not found.
} 
 

Thanks "WeaknessForCat s" (I'm a cat lover so I appreciate your 'name'). What you suggested so makes sense and I will try and incorporate that into the logic somehow (this is not my code so I'm not exactly sure what the person needs to happen if it's not found). I am so curious why this used to work and doesn't now. No code changes were made in this file except to get rid of some compiler warnings for VS2005. I walked through the code using VS 6.0 and I get back the same result. However, the line of code

SRCP_PROTS_LIST* pList = (*listMapIt).second;

doesn't crash the application even when the iterator passed back is end(). Perhaps it's a case of several things being wrong that made it work right before.

anway, thanks again for taking the time to point out something that's pretty darn obvious now.