API Evolution and Deprecation History

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 default allocator uses new anyway, but for the optional pooling allocators 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])

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


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 nothrow, 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>.


Use constexpr and nullptr where appropriate throughout the library.

The library was updated to avoid including <stddef.h> in order to reduce namespace pollution.

Reference-count annotations to assist data race detectors.

Added make_exception_ptr as an alias of copy_exception.


Use of noexcept throughout library.

Partial support for C++11 allocators first appears.

monotonic_clock renamed to steady_clock as required by the final C++11 standard.

A new clocale model for newlib is available.

The library was updated to avoid including <unistd.h> in order to reduce namespace pollution.

Debug Mode was improved for unordered containers.


New random number engines and distributions. Optimisations for random.

New --enable-libstdcxx-verbose configure option

The --enable-libstdcxx-time configure option becomes unnecessary given a sufficiently recent glibc.


Implementation of regex completed.

C++14 library and TS implementations are added.

copy_exception deprecated.

__gnu_cxx::array_allocator deprecated.


ABI transition adds new implementations of several components, using the abi_tag attribute and the __cxx11 inline namespace to distinguish the new entities from the old ones.

  • Use of the new or old ABI can be selected per-translation unit with the Macros.

  • New non-reference-counted string implementation.

  • New list implementation containing a new data member in order to provide O(1) size().

  • New ios_base::failure implementation inheriting from system_error.

C++11 support completed (movable iostreams, new I/O manipulators, Unicode conversion utilities, atomic operations for shared_ptr, functions for notifying condition variables and making futures ready at thread exit).

Changed formatting of floating point types when ios_base::fixed|ios_base::scientific is set in a stream's format flags.

Improved C++14 support and TS implementations.

New random number engines and distributions.

GDB Xmethods for containers and unique_ptr added.

has_trivial_default_constructor, has_trivial_copy_constructor and has_trivial_copy_assign deprecated.


Experimental implementation of the C++ Filesystem TS added.


C++14 support completed.

Support for mathematical special functions (ISO/IEC 29124:2010) added.

Assertions to check function preconditions can be enabled by defining the _GLIBCXX_ASSERTIONS macro. The initial set of assertions are a subset of the checks enabled by the Debug Mode, but without the ABI changes and changes to algorithmic complexity that are caused by enabling the full Debug Mode.


The type of exception thrown by iostreams changed to the cxx11 ABI version of std::ios_base::failure.

Experimental C++17 support added, including most new library features. The meaning of shared_ptr<T[]> changed to match the C++17 semantics.

Macros added.

has_trivial_default_constructor, has_trivial_copy_constructor and has_trivial_copy_assign removed.

Calling a std::bind result as volatile was deprecated for C++17.

Profile Mode was deprecated.


Library Fundamentals TS header <experimental/source_location> added.


Including new C++14 or C++17 headers without a suitable -std no longer causes compilation to fail via #error. Instead the header is simply empty and doesn't define anything.


The exceptions thrown by iostreams can now be caught by handlers for either version of std::ios_base::failure.

Improved experimental C++17 support. Headers <charconv> and <filesystem>. Experimental implementation of the C++17 Filesystem library added.

Experimental C++2a support (to_address and endian).

AddressSanitizer annotations added to std::vector to detect out-of-range accesses to the unused capacity of a vector.

std::char_traits<char16_t>::to_int_type(u'\uFFFF') now returns 0xFFFD, as 0xFFFF is used for std::char_traits<char16_t>::eof().

The extension allowing arithmetic on std::atomic<void*> and types like std::atomic<R(*)()> was deprecated.

The std::uncaught_exception function was deprecated for C++17 mode.

The nested typedefs std::hash::result_type and std::hash::argument_type were deprecated for C++17 mode.

The deprecated iostream members ios_base::io_state, ios_base::open_mode, ios_base::seek_dir, and basic_streambuf::stossc were removed for C++17 mode.

The non-standard C++0x std::copy_exception function was removed.

For -std=c++11, -std=c++14, and -std=c++17 modes the <complex.h> header no longer includes the C99 <complex.h> header.

For the non-default --enable-symvers=gnu-versioned-namespace configuration, the shared library SONAME has been changed to libstdc++.so.8.

The extension allowing containers to be instantiated with an allocator that doesn't match the container's value type is no longer allowed in strict (-std=c++NN) modes, only in -std=gnu++NN modes.


C++17 header <memory_resource> added.

Experimental C++2a support improved, with new headers <bit> and <version> added. Support for new character type char8_t added to char_traits, basic_string, numeric_limits, and relevant locale facets and type traits.

Experimental implementation of the Networking TS library added, with new headers <experimental/buffer>, <experimental/executor>, <experimental/internet>, <experimental/io_context>, <experimental/net>, <experimental/netfwd>, <experimental/socket>, and <experimental/timer>.


Deprecated features removed:

  • Profile Mode
  • __gnu_cxx::array_allocator

The non-standard std::__is_nullptr_t type trait was deprecated.

The std::packaged_task constructors taking an allocator argument are only defined for C++11 and C++14.

Several members of std::allocator were removed for C++20 mode. The removed functionality has been provided by std::allocator_traits since C++11 and that should be used instead.

The type of the std::iterator base class of std::istreambuf_iterator was changed to be consistent for all -std modes. Before GCC 10.1 the base class had one type in C++98 mode and a different type in C++11 and later modes. The type in C++98 mode was changed to be the same as for C++11 and later.

Experimental C++2a support improved, with new headers <concepts>, <ranges>, <compare>, <coroutine>, <numbers>, <span>, and <stop_token> added.

The extension allowing containers to be instantiated with an allocator that doesn't match the container's value type is no longer allowed in C++20 mode, even in non-strict -std=gnu++20 mode.


The --enable-cheaders=c_std configuration was deprecated.

When compiling as C++20, the operator>> overloads for extracting strings into character buffers only work with arrays, not raw pointers.

std::string::reserve(n) will no longer reduce the string's capacity. Calling reserve() with no arguments is equivalent to shrink_to_fit(), but is deprecated. shrink_to_fit() should be used instead.


The std::random_shuffle algorithms are deprecated for C++14 and later. The C++11 std::shuffle algorithm can be used instead.

The std::unexpected function and related typedef and accessors for the unexpected handler are deprecated for C++11 and later. Dynamic exception specifications should be replaced with noexcept.

C++98 adaptable function utilities (std::bind1st, std::unary_function, std::ptr_fun, std::mem_fun_ref etc.) were deprecated for C++11. std::iterator, std::raw_storage_iterator, get_temporary_buffer, and std::not_fun were deprecated for C++17.

Non-standard std::pair constructors were deprecated. A non-standard default argument for vector<bool>::insert(const_iterator, const bool&) was deprecated.

The bitmap, mt, and pool options for --enable-libstdcxx-allocator were removed. For the new option, std::allocator no longer derives from __gnu_cxx::new_allocator; they both derive from std::__new_allocator instead.

std::condition_variable::wait changed to be noexcept(false) to allow thread cancellation exceptions to be thrown from pthread_cond_wait without aborting the process.


Calling a std::bind result as volatile is ill-formed for C++20 and later.


Tunables <variable>glibcxx.eh_pool.obj_count</variable> and <variable>glibcxx.eh_pool.obj_size</variable> were added.

Static library libstdc++exp.a was added to provide the symbols for the experimental C++ Contracts support.


Symbols for the Filesystem TS and C++23 <stacktrace> header were added to the static library libstdc++exp.a.


Deprecate the non-standard overload that allows std::setfill to be used with std::basic_istream.

The extension allowing std::basic_string to be instantiated with an allocator that doesn't match the string's character type is no longer allowed in C++20 mode.