Not really sure how serious this is, but I found this problem installing under RedHat9,

gcc --version
gcc (GCC) 3.2.2 20030222 (Red Hat Linux 3.2.2-5)

Full error message...

g++ -O cd-hit.c++ -c
In file included from /usr/include/c++/3.2.2/backward/iostream.h:31,
from cd-hi.h:22,
from cd-hit.c++:17:
/usr/include/c++/3.2.2/backward/backward_warning.h:32:2: warning: #warning This
file includes at least one deprecated or antiquated header. Please consider using one of the 32 headers found in section 17.4.1.2 of the C++ standard. Examples
include substituting the <X> header for the <X.h> header for C++ includes, or <sstream> instead of the deprecated header <strstream.h>. To disable this warning
use -Wno-deprecated.

And again (same message) from

In file included from /usr/include/c++/3.2.2/backward/iostream.h:31,
from cd-hi.h:22,
from cd-hi-class.c++:22:

Then we get warnings about...

cd-hi-class.c++:497: no matching function for call to `
std::basic_ifstream<char, std::char_traits<char> >::read(int*&, unsigned int
)'

And again (io related functions)...

cd-hi-class.c++:498:
cd-hi-class.c++:516:
cd-hi-class.c++:517:

make: *** [cd-hi-class.o] Error 1