Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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Configuring and building the library

The library has a separately compiled part which should be built as described in the Getting Started guide. One thing should be noted, though. If your application consists of more than one module (e.g. an exe and one or several dll's) that use Boost.Log, the library must be built as a shared object. If you have a single executable or a single module that works with Boost.Log, you may build the library as a static library.

The library supports a number of configuration macros:

Table 1.1. Configuration macros

Macro name

Effect

BOOST_LOG_DYN_LINK

If defined in user code, the library will assume the binary is built as a dynamically loaded library ("dll" or "so"). Otherwise it is assumed that the library is built in static mode. This macro must be either defined or not defined for all translation units of user application that uses logging. This macro can help with auto-linking on platforms that support it.

BOOST_ALL_DYN_LINK

Same as BOOST_LOG_DYN_LINK but also affects other Boost libraries the same way.

BOOST_USE_WINAPI_VERSION

Affects compilation of both the library and user's code. This macro is Windows-specific. Selects the target Windows version for various Boost libraries, including Boost.Log. Code compiled for a particular Windows version will likely fail to run on the older Windows versions, but may improve performance because of using newer OS features. The macro is expected to have an integer value equivalent to _WIN32_WINNT.

BOOST_LOG_NO_THREADS

If defined, disables multithreading support. Affects the compilation of both the library and users' code. The macro is automatically defined if no threading support is detected.

BOOST_LOG_WITHOUT_CHAR

If defined, disables support for narrow character logging. Affects the compilation of both the library and users' code.

BOOST_LOG_WITHOUT_WCHAR_T

If defined, disables support for wide character logging. Affects the compilation of both the library and users' code.

BOOST_LOG_NO_QUERY_PERFORMANCE_COUNTER

This macro is only useful on Windows. It affects the compilation of both the library and users' code. If defined, disables support for the QueryPerformanceCounter API in the timer attribute. This will result in significantly less accurate time readings. The macro is intended to solve possible problems with earlier revisions of AMD Athlon CPU, described here and here. There are also known chipset hardware failures that may prevent this API from functioning properly (see here).

BOOST_LOG_USE_NATIVE_SYSLOG

Affects only compilation of the library. If for some reason support for the native SysLog API is not detected automatically, define this macro to forcibly enable it.

BOOST_LOG_WITHOUT_DEFAULT_FACTORIES

Affects only compilation of the library. If defined, the parsers for settings will be built without any default factories for filters and formatters. The user will have to register all attributes in the library before parsing any filters or formatters from strings. This can substantially reduce the binary size.

BOOST_LOG_WITHOUT_SETTINGS_PARSERS

Affects only compilation of the library. If defined, none of the facilities related to the parsers for settings will be built. This can substantially reduce the binary size.

BOOST_LOG_WITHOUT_DEBUG_OUTPUT

Affects only compilation of the library. If defined, the support for debugger output on Windows will not be built.

BOOST_LOG_WITHOUT_EVENT_LOG

Affects only compilation of the library. If defined, the support for Windows event log will not be built. Defining the macro also makes Message Compiler toolset unnecessary.

BOOST_LOG_WITHOUT_SYSLOG

Affects only compilation of the library. If defined, the support for syslog backend will not be built.

BOOST_LOG_WITHOUT_IPC

Affects only compilation of the library. If defined, the support for interprocess queues will not be built.

BOOST_LOG_NO_SHORTHAND_NAMES

Affects only compilation of users' code. If defined, some deprecated shorthand macro names will not be available.

BOOST_LOG_USE_COMPILER_TLS

Affects only compilation of the library. This macro enables support for compiler intrinsics for thread-local storage. Defining it may improve performance of Boost.Log if certain usage limitations are acceptable. See below for more comments.

BOOST_LOG_USE_STD_REGEX, BOOST_LOG_USE_BOOST_REGEX or BOOST_LOG_USE_BOOST_XPRESSIVE

Affects only compilation of the library. By defining one of these macros the user can instruct Boost.Log to use std::regex, Boost.Regex or Boost.Xpressive internally for string matching filters parsed from strings and settings. If none of these macros is defined then Boost.Log uses Boost.Regex by default. Using std::regex or Boost.Regex typically produces smaller executables, Boost.Regex usually also being the fastest in run time. Using Boost.Xpressive allows to eliminate the dependency on Boost.Regex compiled binary. Note that these macros do not affect filtering expressions created by users.


You can define configuration macros in the bjam command line, like this:

bjam --with-log variant=release define=BOOST_LOG_WITHOUT_EVENT_LOG define=BOOST_USE_WINAPI_VERSION=0x0600 stage

However, it may be more convenient to define configuration macros in the "boost/config/user.hpp" file in order to automatically define them both for the library and user's projects. If none of the options are specified, the library will try to support the most comprehensive setup, including support for all character types and features available for the target platform.

The logging library uses several other Boost libraries that require building too. These are Boost.Filesystem, Boost.System, Boost.DateTime, Boost.Thread and in some configurations Boost.Regex. Refer to their documentation for detailed instructions on the building procedure.

One final thing should be added. The library requires run-time type information (RTTI) to be enabled for both the library compilation and user's code compilation. Normally, this won't need anything from you except to verify that RTTI support is not disabled in your project.

Notes about compiler-supplied intrinsics for TLS

Many widely used compilers support builtin intrinsics for managing thread-local storage, which is used in several parts of the library. This feature is also included in the C++11 standard. Generally, these intrinsics allow for a much more efficient access to the storage than any surrogate implementation, be that Boost.Thread or even native operating system API. However, this feature has several caveats:

The library provides the BOOST_LOG_USE_COMPILER_TLS configuration macro that allows to enable the use of this feature, which will improve the library performance at the cost of these limitations:

Note that the BOOST_LOG_USE_COMPILER_TLS macro only controls use of TLS in Boost.Log but not in other libraries used by Boost.Log. For example, Boost.ASIO uses compiler-supplied TLS by default. In order to build Boost.Log binaries completely free from use of compiler-supplied TLS, this feature has to be disabled in those other libraries as well (in case of Boost.ASIO this can be achieved by defining BOOST_ASIO_DISABLE_THREAD_KEYWORD_EXTENSION when building and using Boost).

Notes about native wchar_t support

Some compilers, most notably MSVC, have an option to disable the native wchar_t type, emulating it with a typedef for one of the standard integral types. From the C++ language perspective this behavior is not conforming but it may be useful for compatibility with some legacy code which is difficult to update.

By default, Boost (and Boost.Log being part of it) is built with native wchar_t enabled. At the time of this writing, user will have to modify Boost.Build to enable the emulation mode. It is possible to build Boost.Log in this mode, but there are several caveats that have to be kept in mind:

Because of that using the emulation mode is discouraged and should be avoided. In future releases of the library its support may be removed completely.


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