## Changelog

#### 2.8, Boost 1.61

General changes:

- The support for `boost::basic_string_ref` and its specializations is deprecated; users are encouraged to switch to `boost::basic_string_view`, which is now supported for output to the formatting streams. The support for `boost::basic_string_ref` will be removed in future releases.
- Added support for limiting the number of stored log files in the target directory of the file collector. The limit can be specified in the `max_files` named parameter to the `make_collector` or `add_file_log` calls or as the "MaxFiles" parameter for the sink in the settings file. Thanks to Erich Keane for the patch. ( #8746)

Bug fixes:

- Fixed various compilation problems for Windows CE.
- Fixed compilation problems on Solaris.
- Added a workaround for MSVC-10 and 11 generating broken code for formatters in some cases. ( #12025)

#### 2.7, Boost 1.60

General changes:

- On Windows, the configuration macro `BOOST_LOG_USE_WINNT6_API` is no longer used by the library. The target Windows version should be configured by defining macro `BOOST_USE_WINAPI_VERSION` to the desired WinAPI version (e.g. 0x0501 for Windows XP). This macro is used in multiple different Boost libraries besides Boost.Log.
- The default target Windows version is now Vista on compilers with recent enough Windows SDK and XP on others. The default is no longer chosen by Boost.Log but by the common WinAPI submodule used by different Boost libraries.
- Changed internal mutex type in the thread-safe queue implementation that is used in asynchronous sink frontends with the `unbounded_fifo_queue` policy. The updated queue has improved performance in case of heavy thread contention (hundreds and thousands of logging threads) on POSIX-compatible systems.

Bug fixes:

- Fixed compilation for Android using Google NDK. ( #11559)
- Fixed compilation of some logging statements, where the first object to be put into stream is not directly supported by `formatting_ostream`. ( #11549)
- Added a workaround for Solaris Studio 12.4, which should fix the compilation of `formatting_ostream`. ( #11545)
- Fixed compilation when native `wchar_t` type is disabled. Added a note of discouragement to the configuration section. ( #11541)
- Fixed exporting symbols from the `boost_log_setup` library on POSIX-like systems.
- Fixed build failure on Nuxi CloudABI.
- Fixed compilation of character decorators.
- Added a workaround for incorrect file name generation in text file sink backend, when the file name contains date/time placeholders. ( #11691)

#### 2.6, Boost 1.59

General changes:

- On systems with symbol visibility support (e.g. Linux) the library is now built with all internal symbols hidden. API symbols still have default visibility, so this shouldn't affect linking with the library.
- Breaking change: The library has been ported to Boost.TypeIndex for its underlying type info management tool. This improved library compatibility with hidden symbol visibility mode on some compilers. This affected the following public interfaces:
  - `invalid_type` exceptions thrown by the library now have `typeindex::type_index` attached as the description of the offending type. The type was previously identified by `type_info_wrapper`.
  - Boost.Exception `type_info_info` error information now contains `typeindex::type_index` instead of `type_info_wrapper`. This is the error info that can be used to obtain the type info from `invalid_type` exceptions.
  - `attribute_value::get_type()` now returns `typeindex::type_index` instead of `type_info_wrapper`. If the `attribute_value` object is empty, the returned `type_index` is default-constructed (i.e. refers to the `void` type). User-defined attribute value implementations should be similarly changed (the `attribute_value::impl::get_type()` virtual method now also returns `typeindex::type_index`).
- `type_info_wrapper` component has been deprecated and will be removed in future releases. Boost.TypeIndex is recommended as a replacement.
- Removed the previously deprecated headers: `boost/log/utility/intrusive_ref_counter.hpp`, `boost/log/utility/explicit_operator_bool.hpp`, `boost/log/utility/empty_deleter.hpp`.
- Added support for building the library for OpenBSD. ( #11446)
- Improved internal implementation of the event synchronization primitive used for asynchronous logging. The updated implementation relies on Boost.Atomic for atomic operations which provides better portability. On Linux the implementation uses futexes directly. ( #11398)
- Changed the format of dates produced by the default formatter constructed from strings (e.g. when initializing the library from a config file). The new format displays months as numbers instead of abbreviated names. This allows for easier log record ordering when post-processing log files. ( #8839)

Bug fixes:

- Fixed incorrect behavior of `attribute_value_set::insert()` and `attribute_value_set` constructor in some cases. The inserted elements could have made some previously inserted elements not findable. The constructor from `attribute_set`s could leave some of the attribute values acquired from attributes not findable. ( #11190)
- Added missing function template exports. ( #11495)

#### 2.5, Boost 1.58

Bug fixes:

- Fixed thread id formatting. The thread identifiers could be presented as zeros on big-endian platforms. Also the lower 4 bits of the ids were lost in the output.
- Fixed process id formatting. Process ids could have misplaced filler zeros. ( #10926)
- Fixed build failure on GNU Hurd.
- Fixed incorrect behavior of text file sink backend in case if free space on the file system gets exhausted. The sink will no longer create lots of empty files in attempt to recover. ( #11016)
- Fixed incorrect behavior of `attribute_set::insert()` in some cases. The inserted elements could have made some previously inserted elements not findable. ( #11106)
- Fixed incorrect behavior of `attribute_value_set::size()` if a large number of attribute values are inserted into the set. ( #11148)

#### 2.4, Boost 1.57

Bug fixes:

- XML character decorator now escapes quote (") characters.
- The exceptions thrown by asynchronous sinks created as a result of initialization from settings are now silently suppressed instead of terminating the application. If special error handling is needed, it is recommended to register a user-defined sink factory. ( #10638)
- Corrected syslog message composition on MSVC, if message length exceeds 1025 bytes. ( #10700)

#### 2.3, Boost 1.56

General changes:

- For Windows targets, the library now compiles for Windows XP by default.
- Added indexing operators with `attribute_name` arguments to `record` and `record_view`. The operators behave the same way as the similar operators of `attribute_value_set` (i.e. return an `attribute_value` identified by the name).
- Added operators for non-const object output to `basic_formatting_ostream`. ( #9389)
- Added new format flags "%c", "%C" and "%F" to the named scope formatter. The new flags allow putting function names and source file names of named scopes into the formatted strings. ( #9263)
- Added support for incomplete and empty markers to the named scope formatter. The markers can be used to customize the scope list presentation when the list is empty or limited by the `depth` named parameter. ( #9123)
- The default presentation for incomplete named scope lists has changed. In previous releases the incomplete marker included a trailing delimiter, for example "scope1<-scope2<-...". From this release the trailing delimiter is omitted, so in the same case the formatting result would be: "scope1<-scope2..." (note the missing trailing "<-").
- Added a support header for `std::regex`. If `boost/log/support/std_regex.hpp` is included, one can use `std::regex` expressions with string matching filters.
- By default Boost.Log uses Boost.Regex internally as the regular expressions backend. Boost.Xpressive was used in previous releases. This backend is used to implement string matching filters parsed from strings or settings. Using Boost.Regex by default results in smaller executables and also better runtime performance.
- Added build configuration macros for regex backend selection. By defining `BOOST_LOG_USE_STD_REGEX`, `BOOST_LOG_USE_BOOST_REGEX` or `BOOST_LOG_USE_BOOST_XPRESSIVE` at Boost.Log build time the user can select which regex implementation will be used by the library internally for the string matching filters parsed from strings and settings. Note that this selection does not affect string matching filters in expressions.

Bug fixes:

- Fixed `dump` manipulator output on AVX2-enabled CPUs (e.g. Intel Haswell).
- Fixed compilation of `get_attribute` method of loggers.
- Fixed a possible race in `locked_backend()` function implementation of synchronous and asynchronous sink frontends.
- Fixed a possible infinite block of the logging threads in the asynchronous sink enqueue methods when `block_on_overflow` strategy was used.
- Added a workaround for ticket #9363.
- Added a workaround for MSVC bug that caused the `add_value` manipulator produce garbage attribute values when using with immediate integer constants. ( #9320)

#### 2.2, Boost 1.55

General changes:

- Added a new configuration macro `BOOST_LOG_WITHOUT_DEFAULT_FACTORIES`. By defining this macro the user can disable compilation of the default filter and formatter factories used by settings parsers. This can substantially reduce binary sizes while still retaining support for settings parsers. Note that when this macro is defined the user will have to register all attributes in the library.
- Rewritten some of the parsers to reduce the compiled binary size. The rewritten parsers are more robust in detecting ambiguous and incorrect input.
- The header `boost/log/utility/intrusive_ref_counter.hpp` is deprecated and will be removed in future releases. Its contents have been reworked and moved to Boost.SmartPtr, as `boost/smart_ptr/intrusive_ref_counter.hpp`.
- The header `boost/log/utility/explicit_operator_bool.hpp` is deprecated and will be removed in future releases. Its contents have been moved to Boost.Utility, as `boost/utility/explicit_operator_bool.hpp`.
- The header `boost/log/utility/empty_deleter.hpp` is deprecated and will be removed in future releases. Its contents have been moved to Boost.Utility, as `boost/utility/empty_deleter.hpp`.

Bug fixes:

- Fixed `timer` attribute generating incorrect time readings on Windows on heavy thread contention when `QueryPerformanceCounter` API was used.
- Fixed a bug in the filter parser that prevented using parsed filters with some attributes. For example, parsed filters didn't work with a string-typed attribute value, if the value was compared to a numeric operand.
- Fixed thread id formatting discrepancies between the default sink and formatters.
- Fixed parsing RotationTimePoint parameter values from settings, when the time point only included time of day (i.e. daily rotation).
- Closed tickets: #8815, #8819, #8915, #8917, #9139, #9140, #9153, #9155.

#### 2.1, Boost 1.54

Breaking changes:

- `basic_formatting_ostream` no longer derives from `std::basic_ostream`, but rather reimplements its and its base classes interface closely. This solves problems with overloading `operator<<` for `basic_formatting_ostream` and user-defined types. This will break user's code if it relied on the inheritance from the standard stream types (such as passing `basic_formatting_ostream` object as an argument to a function receiving `std::basic_ostream`). Please, use the `stream()` member function to access the standard stream. This change will not break the code that outputs user-defined types to a `basic_formatting_ostream` stream while there are only `operator<<` overloads for the standard stream types - the code will compile and use the standard operator overloads, as before.

General changes:

- Removed the use of deprecated macros of Boost.Config.
- Build system improved. On Windows, presence of Message Compiler is now detected automatically, and support for event log is only enabled when the tool is available.
- Fixed compilation when `BOOST_LOG_USE_COMPILER_TLS` configuration macro is defined.
- Fixed compilation of some uses of the `add_value` manipulator with MSVC.
- Added a new `dump` output manipulator for printing binary data.

#### 2.0, 13 April 2013

General changes:

- The library is now compatible with Boost 1.53 or newer. Boost.Filesystem v2 no longer supported.
- The library now does not introduce separate logging cores for different character types. A lot of other library components also became character type agnostic. The application can now use loggers of different character types with the common logging core. The library performs character code conversion as needed. Boost.Locale can be used to construct locale objects for proper encoding conversion.
- The `BOOST_LOG_NO_COMPILER_TLS` configuration macro has been replaced with `BOOST_LOG_USE_COMPILER_TLS` with the opposite meaning. The support for compiler intrinsics for TLS is now disabled by default.
- Added configuration macros `BOOST_LOG_WITHOUT_DEBUG_OUTPUT`, `BOOST_LOG_WITHOUT_EVENT_LOG` and `BOOST_LOG_WITHOUT_SYSLOG`. `BOOST_LOG_NO_SETTINGS_PARSERS_SUPPORT` macro renamed to `BOOST_LOG_WITHOUT_SETTINGS_PARSERS`. The new macros allow to selectively disable support for the corresponding sink backends.
- The library now uses Boost.Xpressive instead of Boost.Regex internally which makes it unnecessary to build the latter in order to use the library. Boost.Regex is still supported on the user's side.
- Made some internal code to detect Windows NT6 API availability at run time, if not explicitly enabled by the `BOOST_LOG_USE_WINNT6_API` macro. The code compiled without the macro defined will still be able run on NT5, but when run on NT6 it will be more efficient. With the macro defined the resulting code will not run on NT5, but will be a little more efficient on NT6 than without the macro.
- Added a concept of a default sink. The default sink is used when there are no sinks configured in the logging core. The sink is synchronous and thread-safe, it requires no configuration and is overridden by any sinks configured in the core by user. The default sink will write log messages to the console, prepending with a timestamp, thread id and severity level.
- Trivial logging no longer implicitly initializes the library. Instead, the default sink is used to display log messages, unless the library is configured otherwise. It is now possible to use both trivial and advanced logging.
- Attribute values can now be added to log records after filtering. Such values do not participate in filtering but can be used by formatters and sinks. Log record message is now one of such attribute values, it is no longer directly accessible from the log record interface.
- Formatters and sinks no longer operate on log records but rather on `record_view`s. Records are now moved from when pushed to the core for further processing. This is done in order to eliminate the possibility of unsafe record modification after pushing to the core. As a consequence, log records can no longer be copied, only moving is allowed. Record views can be copied and moved; copying is a shallow operation.
- The implementation now provides several stream manipulators. Notably, the `to_log` manipulator allows to customize formatting for particular types and attributes without changing the regular streaming operator. Also, the `add_value` manipulator can be used in logging expressions to attach attribute values to the record.
- Made a lot of improvements to speedup code compilation.

Attributes:

- Changed the interface and the way of handling attribute values. The value is now a pimpl wrapper around the value holder. The `attribute_value` class in various components of the library is no longer pointed to with `shared_ptr`s but instead is handled by value. This allowed to simplify attribute value handling in simple cases.
- Similarly to attribute values, the interface of attributes has been reworked in the pimpl fashion. All attributes now derive from the `attribute` base class, which holds the reference to the implementation. All attributes now have to be created by value rather than wrapped into `shared_ptr` by user, which makes the code more concise.
- Added support for casting attributes from the base class `attribute` to the actual attribute type. This can be useful when the concrete attribute factory provides additional interfaces.
- The attribute value no longer has the `get` method. Use the `extract` function as a replacement.
- The key type of attribute sets and attribute values set has been changed. The new key type is called `attribute_name`. It is constructible from strings, so in most cases users won't need to change the code. See here for more information.
- Attribute values view have been renamed to attribute value set. The container now supports adding more attribute values after being constructed.
- Attribute sets and attribute value sets no longer maintain order of elements. Although it wasn't stated explicitly, the containers used to be ordered associative containers. Now the order of elements is unspecified. The implementation has been reworked to speed up insertion/removal of attributes, as well as attribute lookup and values set construction. The drawback is that memory footprint may get increased in some cases.
- Attribute sets now use small memory pools to speed up element insertion/removal.
- The header `scoped_attribute.hpp` moved from `utility` to the `attributes` directory. The header `attribute_value_extractor.hpp` in `utility` has been replaced with headers `boost/log/attributes/value_extraction.hpp` and `boost/log/attributes/value_visitation.hpp` in the `attributes` directory. The two new headers define the revised API of attribute value extraction and visitation, respectively. See here for more details.
- Scoped attribute macros simplified. The attribute constructor arguments are specified next to the attribute type and tag type is no longer required.
- The `current_thread_id` attribute no longer uses `boost::thread::id` type for thread identification. An internal type is used instead, the type is accessible as `current_thread_id::value_type`. The new thread ids are taken from the underlying OS API and thus more closely correlate to what may be displayed by debuggers and system diagnostic tools.
- Added `current_process_name` attribute. The attribute generates a string with the executable name of the current process.
- The `functor` attribute has been renamed to `function`. The generator function has been renamed from `make_functor_attr` to `make_function`. The header has been renamed from `functor.hpp` to `function.hpp`.

Logging sources:

- Fixed compilation problems with exception handling logger feature.
- Global logger storage made more friendly to the setups in which hidden visibility is set by default.
- Added the macros for separated global logger declaration and definition. Old macros have been renamed to better reflect their effect (`BOOST_LOG_DECLARE_GLOBAL_LOGGER_INIT` to `BOOST_LOG_INLINE_GLOBAL_LOGGER_INIT`, `BOOST_LOG_DECLARE_GLOBAL_LOGGER` to `BOOST_LOG_INLINE_GLOBAL_LOGGER_DEFAULT`, `BOOST_LOG_DECLARE_GLOBAL_LOGGER_CTOR_ARGS` to `BOOST_LOG_INLINE_GLOBAL_LOGGER_CTOR_ARGS`). Also, the macros no longer define the `get_logger` free function for logger acquisition. Use `logger::get` instead. See here for more information.
- The channel logger now supports changing the channel name after construction. The channel name can be set either by calling the modifier method or by specifying the name in the logging statement. Added `BOOST_LOG_STREAM_CHANNEL` and `BOOST_LOG_STREAM_CHANNEL_SEV` (as well as their shorthands `BOOST_LOG_CHANNEL` and `BOOST_LOG_CHANNEL_SEV`) macros that allow to specify channel name for the log record.

Logging sinks:

- Types for integral constants for syslog and event log were renamed to drop the `_t` suffix.
- Formatting functionality moved to sink frontends. Sink backends that support record formatting derive from the `basic_formatting_sink_backend` class template, which indicates to the frontend that record formatting is required. This breaks user-side API of the library: the formatter and locale has to be set to the frontend rather than backend.
- Formatting support no longer makes frontend thread synchronization mandatory. Formatting is done prior to locking for processing the record in the backend and can be performed concurrently in multiple threads.
- Added support for flushing sinks. A sink backend that supports flushing has to define public method with the following signature: `void flush()`.
- Asynchronous sink frontend reworked, ordering asynchronous sink removed. The `asynchronous_sink` class template now allows to specify record queueing strategy. Several strategies provided, including `unbounded_fifo_queue` (the default) and `unbounded_ordering_queue` which cover the functionality of asynchronous sink frontends in 1.x releases. See the asynchronous sink frontend docs for more details.
- Lock-free FIFO record queueing in asynchronous sinks reworked to reduce log record processing stalls.
- Added `Append` configuration file parameter for text file sinks. If this parameter is set to `true`, the sink will append log records to the existing log file instead of overwriting it.
- Added bounded variants of asynchronous sink frontends. Implemented two strategies to handle queue overflows: either log records are dropped or logging threads are blocked until there is space in the queue.

Filters and formatters:

- As a result of character type unification, filters no longer depend on the character type.
- Two new types were introduced to dynamically store filters and formatters: `filter` and `basic_formatter`. Both new types implement type erasure and provide function calling operators to invoke the stored filter or formatter.
- Filters and formatters were rewritten. The new implementation is based on Boost.Phoenix and resides in the `expressions` namespace. Attribute placeholders are now interoperable with other template expressions based on Boost.Phoenix. All template expression headers now reside in the `expressions` subdirectory.
- The library now supports defining keywords for attributes (see `BOOST_LOG_ATTRIBUTE_KEYWORD` macro). Keywords can be used in template expressions instead of attribute placeholders and also as a key in container lookups.
- Filters and formatters do not throw exceptions by default when an attribute value cannot be used to complete the function (e.g. when the value is missing or has inappropriate type). The offending filter subexpression will return `false` in such cases, the formatter will result in empty string instead of the value. The behavior can be changed by calling `or_default` or `or_throw` member functions on the attribute value placeholder in the filtering/formatting expression.
- Date and time formatter implementation is not based on Boost.DateTime IO facets anymore. The new implementation improves formatting performance. The formatter has been renamed to `format_date_time`.
- Named scope formatter now supports scope format specification. The scope format can include the scope name, as well as file name and line number. The formatter has been renamed to `format_named_scope`.
- Character decorators were renamed to `c_decor`, `c_ascii_decor`, `xml_decor` and `csv_decor`. The generic character decorator is named `char_decor` now.
- Added a new channel severity filter. The filter allows to setup severity thresholds for different channels. The filter checks log record severity level against the threshold corresponding to the channel the record belongs to.

Documentation changes:

- Most code examples from the docs have been extracted into compilable standalone examples, which can be used for testing and experimenting with the library.
- Added a lot of cross-references to the documentation, which should simplify navigation.

Miscellaneous:

- Fixed a bug: the logging core could enter an infinite loop inside `push_record` if a sink throws and the exception is suppressed by the exception handler set in the core.
- Changed the type dispatching implementation to reduce the usage of virtual functions. This greatly reduced the library size.
- Type dispatchers made more friendly to the setups in which hidden visibility is set by default.
- The interface of type dispatchers changed. The dispatcher now returns `type_visitor` instance by value, and the visitor is no longer a base for the actual receiver of the dispatched value. Instead, the visitor now refers to the receiver, if one is capable to consume the value. The `visit` method has been renamed to `operator ()`. The static type dispatcher now requires a reference to the receiver on construction, it doesn't imply that the receiver derives from the dispatcher anymore.
- The `slim_string` utility has been removed. There is no replacement.
- The library now uses many features from the latest C++ standard (aka C++11). For instance, many library components now support move semantics. Boost.Move is used for move emulation on C++03-compatible compilers.

#### 1.1, 02 December 2011

This release mostly fixes bugs in the code and documentation.

- Added support for Boost.Filesystem v3.
- A number of bugs fixed.
- Corrections in the documentation.

#### 1.0, 09 May 2010

This release mostly fixes bugs in the code and documentation. The next major release (2.0) will contain breaking changes and feature additions. The 1.0 branch will not receive any feature updates.

- Added some optimization for thread local storage. In Windows setups, if you dynamically load Boost.Log binaries during the application run time, this optimization may lead to crashes. In that case, you may disable it by defining `BOOST_LOG_NO_COMPILER_TLS` during the library build process. The macro also affects other platforms, which may be useful if your compiler does not support TLS.
- Added a few public accessors and convenience constructors to severity and channel loggers.
- Added ability to rotate log files at the specified time points. The `rotation_interval` keyword is no longer available. The same functionality is achieved with the new `time_based_rotation` keyword and the `rotation_at_time_interval` predicate. See here for more details.
- Improved support for MinGW and Cygwin.
- A number of bugs fixed. Added workarounds to compile on GCC 4.2.
- Lots of corrections in the documentation.

#### Release Candidate 4, 08 Jan 2010

- Substantial documentation improvement. The tutorial section has been reorganized.
- Library headers have been reorganized. Some other Boost libraries that were previously included by headers have been made optional. Such dependencies have been extracted into separate headers in the `support` directory. Top level library headers now mostly include nested headers.
- Keywords have moved into a dedicated `keywords` namespace. There are no longer nested `keywords` namespaces in `sinks`, `attributes`, etc. All keywords have been extracted into separate headers in the `keywords` directory.
- Removed rotating file stream. As a replacement, a new file sink has been added, which allows to achieve the same results ans adds a few more features.
- Added a new multifile sink backend.
- Added a new ordering asynchronous sink frontend.
- The syslog sink backend is now supported on Windows, too. The sink no longer requires native support for POSIX API for syslog, but is able to send syslog packets to a remote server over UDP.
- Loggers implementation has been improved. Feature composition mechanism has been cleaned up.
- Added support for scoped logging. There is now a distinct log record entity, which is returned by the core as a result of filtering. It is possible to fill in the record message in any way the user wants, not necessarily with a streaming expression. The record object is now processed by sinks and formatters.
- Added support for exception control. User can register exception handlers at one of the three layers: for a particular sink, at the core layer, and for a particular logger (given that it has the appropriate feature). Sinks and core will not suppress exceptions by default. Filter and formatters will throw if the requested attribute value is not found.
- Added a few new formatters, called character decorators. These can be useful to post-process the formatted output before passing it on to the sink.
- Added attributes for thread and process identifiers. These identifiers are automatically added after the call to `add_common_attributes`.
- Helper initialization functions, such as `init_log_to_file` now accept more customization options as named arguments.
- A new initialization interface has been exposed. One can fill a settings container and use it to initialize the library.
- The library setup support code has been extracted into a separate binary. Further on, this binary will be made optional to build.
- Added a new mode of logging, called trivial logging. In this mode the library requires no initialization at all, however it does not offer many ways of customization.
- A number of bugs fixed.
- A few optimizations added to improve multithreaded applications performance.
- Removed some bug workarounds for older Boost releases. The library now requires Boost 1.39 or newer.

#### Release Candidate 3, 08 Feb 2009

- Substantial documentation improvement.
- Added several Windows-specific sinks: Event Log (simplified and advanced), Windows debugger and experimental Event Trace for Windows Vista and later.
- Loggers now consist of a number of independent features that can be composed the way the user needs. User-defined features can be developed and injected into the mix.
- Attribute value extractors improved. With the new extract function attribute values can be extracted from the attribute values view by employing lambda functors.
- Some files and classes were moved or renamed to improve code clarity and shorten names.
- A number of bugs fixed.
- Added tests.

#### Release Candidate 2

No one really remembers these dark ages...