I'm running Debian so the package names may be diffent, but you might as well give it a try:
robin@Robin-Latitude-D620 ~ $ aptitude search libstdc++
v libstdc++-dev -
v libstdc++-dev-armel-cross -
v libstdc++-dev-armel-dcv1 -
p libstdc++5 - The GNU Standard C++ Library v3
i libstdc++6 - De GNU stdc++ bibliotheek versie 3
p libstdc++6-4.3-dbg - The GNU Standard C++ Library v3 (debugging
p libstdc++6-4.3-dev - De GNU Standaard C++ bibliotheek v3 (voor
p libstdc++6-4.3-doc - The GNU Standard C++ Library v3 (documenta
p libstdc++6-4.3-pic - The GNU Standard C++ Library v3 (shared li
p libstdc++6-4.4-dbg - The GNU Standard C++ Library v3 (debugging
p libstdc++6-4.4-dbg-armel-cross - The GNU Standard C++ Library v3 (debugging
i A libstdc++6-4.4-dev - The GNU Standard C++ Library v3 (developme
p libstdc++6-4.4-dev-armel-cross - De GNU Standaard C++ bibliotheek v3 (voor
p libstdc++6-4.4-doc - The GNU Standard C++ Library v3 (documenta
p libstdc++6-4.4-pic - The GNU Standard C++ Library v3 (shared li
p libstdc++6-4.4-pic-armel-cross - The GNU Standard C++ Library v3 (shared li
p libstdc++6-4.5-dbg - The GNU Standard C++ Library v3 (debugging
p libstdc++6-4.5-dbg-armel-cross - The GNU Standard C++ Library v3 (debugging
p libstdc++6-4.5-dev - The GNU Standard C++ Library v3 (developme
p libstdc++6-4.5-dev-armel-cross - De GNU Standaard C++ bibliotheek v3 (voor
p libstdc++6-4.5-doc - The GNU Standard C++ Library v3 (documenta
p libstdc++6-4.5-pic - The GNU Standard C++ Library v3 (shared li
p libstdc++6-4.5-pic-armel-cross - The GNU Standard C++ Library v3 (shared li
p libstdc++6-armel-cross - The GNU Standard C++ Library v3
v libstdc++6-armel-dcv1 -
v libstdc++6-dbg-armel-dcv1 -
v libstdc++6-dev-armel-dcv1 -
v libstdc++6-pic-armel-dcv1
I think libstdc++6-4.5-doc might be what you're looking for? Maybe the package name is the same in your distro's repositories?
Anyway, I don't know yum very well (only used it twice), but if I remember correctly, it's got a search command as well, just like aptitude has.
Doesn't yum search libstdc++ give you anything useful?
--
Found something that's probably more useful to you: ftp://fr2.rpmfind.net/linux/fedora/releases/15/Everything/i386/os/Packages/libstdc++-docs-4.6.0-6.fc15.i686.rpm
Found it here: http://fr2.rpmfind.net/linux/rpm2html/search.php?query=libstdc%2B%2B-docs
yum searchto see if you have a typo in the package name? – Didier Trosset May 30 '11 at 15:02