[PATCH] New warning when using memset etc on std class data

[Daniel Marjamäki]

Hello!

I try again (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20131111/093111.html).

Sometimes memset is used on classes. In general this is ok. However using memset/memcpy/memmove on standard stl classes, such as std::string, is a bad idea. This patch adds warnings when memset is used on a class that has stl class members.

My patch is hardcoded for std classes. I normally would not suggest hard coding. However when it comes to standard C/C++ classes and functions I wonder if it's ok with hard coding?

There was a comment to make this check more generic by looking at the classes instead. I don't see any trivial class property that makes using memset on the class bad, except when there is a virtual table and when there are reference members. Warnings about that doesn't mean there will be warnings about STL classes.

We could perhaps detect by full analysis of the control and data flow through constructors and functions that it's bad to use memset on a class if it causes for instance memory leak or division by zero.
However:
 * It might not always be possible to see some bad behaviour when std classes are overwritten.
 * I'd say a warning message such as "using memset on class that contains std::string member" is more clear than some more generic "memory leak".

Best regards,
Daniel Marjamäki