API Evolution and Deprecation History
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## API Evolution and Deprecation History

A list of user-visible changes, in chronological order

### `3.0`

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>`.

### `3.1`

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>`.

### `3.2`

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.

### `3.3`

### `3.4`

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.

### `4.0`

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>`.

### `4.1`

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>`.

### `4.2`

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>`.

### `4.3`

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.

### `4.4`

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`.

### `4.5`

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>`.

### `4.6`

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`.

### `4.7`

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.

### `4.8`

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.

### `4.9`

Implementation of `regex` completed.

C++14 library and TS implementations are added.

`copy_exception` deprecated.

`__gnu_cxx::array_allocator` deprecated.

### `5`

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.

#### `5.3`

Experimental implementation of the C++ Filesystem TS added.

### `6`

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.

### `7`

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.

Profile Mode was deprecated.

#### `7.2`

Library Fundamentals TS header `<experimental/source_location>` added.

#### `7.3`

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.

### `8`

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`.

### `9`

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>`.

### `10`

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.

### `11`

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.

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