Where is this backward_warning.h #warning coming from?

Question

Without looking through every single source file in my XCode project, is there a way to find out which #include is triggering the following 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 <iostream> instead of the deprecated header 
<iostream.h>. To disable this warning use -Wno-deprecated.

Clicking on the error in XCode just opens the backward_warning.h file, which is totally useless.

I know what the warning means, I know how to fix it (when I see the file in question and can look at its #includes)... but I just don't know how to find the file causing the error!

Answer 1

Use the -H option to GCC - that will list the header files that are being included (along with a nesting indication so you can see what file is including which header).

With -H the error will be placed in the output stream clearly showing how the compiler got to backward_warning.h.

For example, when I include hash_map, I'd see:

mikeb@ubuntu:~$ g++  -H -c test.cpp
. /usr/include/c++/4.4/backward/hash_map
.. /usr/include/c++/4.4/backward/backward_warning.h
In file included from /usr/include/c++/4.4/backward/hash_map:60,
                 from test.cpp:3:
/usr/include/c++/4.4/backward/backward_warning.h:28: warning: #warning This file
includes at least one deprecated or antiquated header which may be removed without
further notice at a future date. Please use a non-deprecated interface with equivalent 
functionality instead. For a listing of replacement headers and interfaces, consult 
the file backward_warning.h. To disable this warning use -Wno-deprecated.

... a bunch of snipped output ...

As an aside, /showIncludes performs the same function in MSVC.

Answer 2

As you stated, the file /usr/include/c++/4.2.1/backward/backward_warning.h contains the text you quote. The headers which include backward_warning.h are:

• /usr/include/c++/4.2.1/backward/algo.h
• /usr/include/c++/4.2.1/backward/algobase.h
• /usr/include/c++/4.2.1/backward/alloc.h
• /usr/include/c++/4.2.1/backward/bvector.h
• /usr/include/c++/4.2.1/backward/complex.h
• /usr/include/c++/4.2.1/backward/defalloc.h
• /usr/include/c++/4.2.1/backward/deque.h
• /usr/include/c++/4.2.1/backward/fstream.h
• /usr/include/c++/4.2.1/backward/function.h
• /usr/include/c++/4.2.1/backward/hash_map.h
• /usr/include/c++/4.2.1/backward/hash_set.h
• /usr/include/c++/4.2.1/backward/hashtable.h
• /usr/include/c++/4.2.1/backward/heap.h
• /usr/include/c++/4.2.1/backward/iomanip.h
• /usr/include/c++/4.2.1/backward/iostream.h
• /usr/include/c++/4.2.1/backward/istream.h
• /usr/include/c++/4.2.1/backward/iterator.h
• /usr/include/c++/4.2.1/backward/list.h
• /usr/include/c++/4.2.1/backward/map.h
• /usr/include/c++/4.2.1/backward/multimap.h
• /usr/include/c++/4.2.1/backward/multiset.h
• /usr/include/c++/4.2.1/backward/new.h
• /usr/include/c++/4.2.1/backward/ostream.h
• /usr/include/c++/4.2.1/backward/pair.h
• /usr/include/c++/4.2.1/backward/queue.h
• /usr/include/c++/4.2.1/backward/rope.h
• /usr/include/c++/4.2.1/backward/set.h
• /usr/include/c++/4.2.1/backward/slist.h
• /usr/include/c++/4.2.1/backward/stack.h
• /usr/include/c++/4.2.1/backward/stream.h
• /usr/include/c++/4.2.1/backward/streambuf.h
• /usr/include/c++/4.2.1/backward/strstream
• /usr/include/c++/4.2.1/backward/tempbuf.h
• /usr/include/c++/4.2.1/backward/tree.h
• /usr/include/c++/4.2.1/backward/vector.h

Therefore, the code you are compiling must be including a header such as:

#include <vector.h>

instead of the preferred:

#include <vector>

And the compiler is getting fussy about it. The fix is to find the code which includes the pre-standard header and update it to use the standard header.

(You get similar warnings about deprecated functions if you compile git - the functions are the SHA1 functions from OpenSSL. It is a nuisance, to be polite about it.)