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`. See this note for details as to why this was something needing improvement.

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.1. 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.2. 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++0x

  `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.

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