Reading pathnames from registry

I am reading a pathname from the registry and storing it in a char*.  For example "C:\Winnt\file.txt" is stored in a char*.  Now, when I want to open up this file, the "\"'s are escape sequences so the stream that I am trying to open doesn't exist (C:Winntfile.txt).  So my question is how do I add the escape sequence "\" in front of the "\"'s already in the char*?  Is there a way when reading from the registry to automatically add these extra slashes?  If not, how can I search for the single slashes in the string?