A list of user-visible changes, in chronological order
Extensions moved to include/ext.
  
Include files from the SGI/HP sources that pre-date the ISO standard
are added. These files are placed into
the include/backward directory and a deprecated warning
is added that notifies on inclusion (-Wno-deprecated
deactivates the warning.)
Deprecated include backward/strstream added.
Removal of include builtinbuf.h, indstream.h, parsestream.h, PlotFile.h, SFile.h, stdiostream.h, and stream.h.
Extensions from SGI/HP moved from namespace std
to namespace __gnu_cxx. As part of this, the following
new includes are
added: ext/algorithm, ext/functional, ext/iterator, ext/memory, and ext/numeric.
Extensions to basic_filebuf introduced: __gnu_cxx::enc_filebuf, and __gnu_cxx::stdio_filebuf.
Extensions to tree data structures added in ext/rb_tree.
Removal of ext/tree, moved to backward/tree.h.
Symbol versioning introduced for shared library.
Removal of include backward/strstream.h.
Allocator changes. Change __malloc_alloc to malloc_allocator and __new_alloc to new_allocator. 
 For GCC releases from 2.95 through the 3.1 series, defining
   __USE_MALLOC on the gcc command line would change the
   default allocation strategy to instead use  malloc and
   free. For the 3.2 and 3.3 release series the same
   functionality was spelled _GLIBCXX_FORCE_NEW. From
   GCC 3.4 onwards the functionality is enabled by setting
   GLIBCXX_FORCE_NEW in the environment, see
   the mt allocator chapter
   for details.
   
Error handling in iostreams cleaned up, made consistent.
Large file support.
 Extensions for generic characters and char_traits added in ext/pod_char_traits.h.
Support for wchar_t specializations of basic_filebuf enhanced to support UTF-8 and Unicode, depending on host. More hosts support basic wchar_t functionality.
Support for char_traits beyond builtin types.
Conformant allocator class and usage in containers. As
part of this, the following extensions are
added: ext/bitmap_allocator.h, ext/debug_allocator.h, ext/mt_allocator.h, ext/malloc_allocator.h,ext/new_allocator.h, ext/pool_allocator.h.
This is a change from all previous versions, and may require
source-level changes due to allocator-related changes to structures
names and template parameters, filenames, and file locations. Some,
like __simple_alloc, __allocator, __alloc,  and 
_Alloc_traits have been removed.
Default behavior of std::allocator has changed.
   Previous versions prior to 3.4 cache allocations in a memory
   pool, instead of passing through to call the global allocation
   operators (i.e., __gnu_cxx::pool_allocator).  More
   recent versions default to the
   simpler __gnu_cxx::new_allocator.
 Previously, all allocators were written to the SGI
   style, and all STL containers expected this interface. This
   interface had a traits class called _Alloc_traits that
   attempted to provide more information for compile-time allocation
   selection and optimization. This traits class had another allocator
   wrapper, __simple_alloc<T,A>, which was a
   wrapper around another allocator, A, which itself is an allocator
   for instances of T. But wait, there's more:
   __allocator<T,A> is another adapter.  Many of
   the provided allocator classes were SGI style: such classes can be
   changed to a conforming interface with this wrapper:
   __allocator<T, __alloc> is thus the same as
   allocator<T>.
   
 The class allocator used the typedef
   __alloc to select an underlying allocator that
   satisfied memory allocation requests. The selection of this
   underlying allocator was not user-configurable.
   
Table B.6. Extension Allocators
| Allocator (3.4) | Header (3.4) | Allocator (3.[0-3]) | Header (3.[0-3]) | 
|---|---|---|---|
| __gnu_cxx::new_allocator<T> | ext/new_allocator.h | std::__new_alloc | memory | 
| __gnu_cxx::malloc_allocator<T> | ext/malloc_allocator.h | std::__malloc_alloc_template<int> | memory | 
| __gnu_cxx::debug_allocator<T> | ext/debug_allocator.h | std::debug_alloc<T> | memory | 
| __gnu_cxx::__pool_alloc<T> | ext/pool_allocator.h | std::__default_alloc_template<bool,int> | memory | 
| __gnu_cxx::__mt_alloc<T> | ext/mt_allocator.h | ||
| __gnu_cxx::bitmap_allocator<T> | ext/bitmap_allocator.h | 
Releases after gcc-3.4 have continued to add to the collection of available allocators. All of these new allocators are standard-style. The following table includes details, along with the first released version of GCC that included the extension allocator.
Table B.7. Extension Allocators Continued
| Allocator | Include | Version | 
|---|---|---|
| __gnu_cxx::array_allocator<T> | ext/array_allocator.h | 4.0.0 | 
| __gnu_cxx::throw_allocator<T> | ext/throw_allocator.h | 4.2.0 | 
Debug mode first appears.
Precompiled header support PCH support.
Macro guard for changed, from _GLIBCPP_ to _GLIBCXX_.
Extension ext/stdio_sync_filebuf.h added.
Extension ext/demangle.h added.
TR1 features first appear.
Extension allocator ext/array_allocator.h added.
Extension codecvt specializations moved to ext/codecvt_specializations.h.
Removal of ext/demangle.h.
Removal of cassert from all standard headers: now has to be explicitly included for std::assert calls.
 Extensions for policy-based data structures first added. New includes,
types, namespace pb_assoc.
 Extensions for typelists added in ext/typelist.h.
 Extension for policy-based basic_string first added: __gnu_cxx::__versa_string in ext/vstring.h.
 Default visibility attributes applied to namespace std. Support for -fvisibility.
TR1 random, complex, and C compatibility headers added.
 Extensions for concurrent programming consolidated
into ext/concurrence.h and ext/atomicity.h,
including change of namespace to __gnu_cxx in some
cases. Added types
include _Lock_policy, __concurrence_lock_error, __concurrence_unlock_error, __mutex, __scoped_lock.
 Extensions for type traits consolidated
into ext/type_traits.h. Additional traits are added
(__conditional_type, __enable_if, others.)
 Extensions for policy-based data structures revised. New includes,
types, namespace moved to __pb_ds.
 Extensions for debug mode modified: now nested in namespace
std::__debug and extensions in namespace
__gnu_cxx::__debug.
 Extensions added: ext/typelist.h
and ext/throw_allocator.h.
C++0X features first appear.
TR1 regex and cmath's mathematical special function added.
Backward include edit.
Removed
algobase.h algo.h alloc.h bvector.h complex.h
defalloc.h deque.h fstream.h function.h hash_map.h hash_set.h
hashtable.h heap.h iomanip.h iostream.h istream.h iterator.h
list.h map.h multimap.h multiset.h new.h ostream.h pair.h queue.h rope.h set.h slist.h stack.h streambuf.h stream.h tempbuf.h
tree.h vector.h
  
Added
  hash_map and hash_set
  
Added in C++11
    auto_ptr.h and binders.h
  
Header dependency streamlining.
algorithm no longer includes climits, cstring, or iosfwd 
bitset no longer includes istream or ostream, adds iosfwd 
functional no longer includes cstddef
iomanip no longer includes istream, istream, or functional, adds ioswd 
numeric no longer includes iterator
string no longer includes algorithm or memory
valarray no longer includes numeric or cstdlib
tr1/hashtable no longer includes memory or functional
tr1/memory no longer includes algorithm
tr1/random no longer includes algorithm or fstream
Debug mode for unordered_map and unordered_set.
Parallel mode first appears.
Variadic template implementations of items in tuple and
    functional.
Default what implementations give more elaborate
    exception strings for bad_cast,
    bad_typeid, bad_exception, and
    bad_alloc.
PCH binary files no longer installed. Instead, the source files are installed.
Namespace pb_ds moved to __gnu_pb_ds.
C++0X features.
Added.
    atomic,
    chrono,
    condition_variable,
    forward_list,
    initializer_list,
    mutex,
    ratio,
    thread
  
Updated and improved.
    algorithm,
    system_error,
    type_traits
  
Use of the GNU extension namespace association converted to inline namespaces.
    Preliminary support for initializer_list
    and defaulted and deleted constructors in container classes.
  
    unique_ptr.
  
    Support for new character types char16_t
    and char32_t added
    to char_traits, basic_string, numeric_limits,
    and assorted compile-time type traits.
  
    Support for string conversions to_string
    and to_wstring.
  
    Member functions taking string arguments were added to iostreams
    including basic_filebuf, basic_ofstream,
    and basic_ifstream.
  
    Exception propagation support,
    including exception_ptr, current_exception, copy_exception,
    and rethrow_exception.
  
Uglification of try to __try
and catch to __catch.
  
Audit of internal mutex usage, conversion to functions returning static local mutex.
 Extensions
added: ext/pointer.h
and ext/extptr_allocator.h. Support
for non-standard pointer types has been added
to vector
and forward_list.
C++0X features.
Added.
    functional,
    future,
    random
  
Updated and improved.
    atomic,
    system_error,
    type_traits
  
Add support for explicit operators and standard layout types.
Profile mode first appears.
Support for decimal floating-point arithmetic, including decimal32, decimal64, and decimal128.
Python pretty-printers are added for use with appropriately-advanced versions of gdb.
Audit for application of function attributes notrow, const, pure, and noreturn.
The default behavior for comparing typeinfo names changed, so
in typeinfo, __GXX_MERGED_TYPEINFO_NAMES
now defaults to zero.
 Extensions modified: ext/throw_allocator.h.