[unwind]

Uh, okay. I didn't read the original, sounds somewhat scary.

Anyway, please don't cast the return value of malloc() in C (http://stackoverflow.com/a/605858/28169).

Also, of course len should be const and sizeof (char) should be removed. Also testing whether malloc() succeeded before relying on the result being valid is a good idea (but perhaps there's machinery in place to abort on error), as is deciding what to do if the input string is NULL.

[dchest]

Anyway, please don't cast the return value of malloc() in C (http://stackoverflow.com/a/605858/28169).

It's C++.