I have to check some methods of std::string (thats a manual page from libstdc++6-doc package).
when i type "std::string" in search box in yelp_2.14 I get a lot of other
links insetead the correct one.

I can run juest
$ pinfo std::string
and It shows me what I needed

I can do the same in konqueror typing main:/std::string in the address field.

I also have old yelp_2.4 on the other machine (the lastest
usable version of this progam), and even here typing std::string
takes my directly to the right manual page.

Why the newer version is broken ?

But it is not possible to find this manual by entering it's name (title).

[Screenshot attached]

Hi,

I forwarded this bug report to the upstream developers, I suggest you
subscribe to this bug report and add any comments there,
http://bugzilla.gnome.org/show_bug.cgi?id=399850