g++ 4.6 issue no <bits/c++config.h> file as required by the header cstring

Question

There is no file called bits/c++config.h in the c++ include directory which is required by the cstring header file. But when I include the the header cstring and compile with g++, it does not give me error. The problem occurred when I tried to compile the program with clang++ compiler in the following way.

$clang++ -cc1 -I/usr/include -I/usr/include/c++/4.6.1 -I/usr/lib/gcc/i686-linux-gnu/4.6.1 -I/usr/include/i386-linux-gnu -I opt_149739_build/include hello.cpp

In file included from /media/space/hello.cpp:2:
In file included from /media/space/opt_149739_build/include/clang/Driver/Driver.h:13:
In file included from /media/space/opt_149739_build/include/clang/Basic/Diagnostic.h:17:
In file included from /media/space/opt_149739_build/include/clang/Basic/DiagnosticIDs.h:18:
In file included from /media/space/opt_149739_build/include/llvm/ADT/StringRef.h:14:
/usr/include/c++/4.6.1/cstring:42:10: fatal error: 'bits/c++config.h' file not found
#include <bits/c++config.h>

I am using g++ 4.6.1 on Ubuntu 11.04

What went wrong?

Answer 1

The file bits/c++config.h is the platform specific include relative to the current compiler, so it is hidden in another directory, searched by default by g++, but not by clang++, as it seems.

In my machine, running locate c++config.h gives the following (relevant) files:

/usr/include/c++/4.6/i686-linux-gnu/64/bits/c++config.h
/usr/include/c++/4.6/i686-linux-gnu/bits/c++config.h

The first one is for 64-bits and the second one for 32-bits.

So just add -I/usr/include/c++/4.6/i686-linux-gnu or -I/usr/include/c++/4.6/i686-linux-gnu/64 or whatever you need for your platform.

Answer 2

It can be related to how clang++ search its headers files.

You'll find a sample patch of how they fix it for fedora 15, 4 months ago, here.

See this red hat bugzilla post for more info.