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Using Boost.Asio

Supported Platforms

The following platform and compiler combinations are regularly tested:

The following platforms may also work:


The following libraries must be available in order to link programs that use Boost.Asio:

Furthermore, some of the examples also require the Boost.Thread, Boost.Date_Time or Boost.Serialization libraries.

[Note] Note

With MSVC or Borland C++ you may want to add -DBOOST_DATE_TIME_NO_LIB and -DBOOST_REGEX_NO_LIB to your project settings to disable autolinking of the Boost.Date_Time and Boost.Regex libraries respectively. Alternatively, you may choose to build these libraries and link to them.

Building Boost Libraries

You may build the subset of Boost libraries required to use Boost.Asio and its examples by running the following command from the root of the Boost download package:

b2 --with-system --with-thread --with-date_time --with-regex --with-serialization stage

This assumes that you have already built b2. Consult the Boost.Build documentation for more details.

Optional separate compilation

By default, Boost.Asio is a header-only library. However, some developers may prefer to build Boost.Asio using separately compiled source code. To do this, add #include <boost/asio/impl/src.hpp> to one (and only one) source file in a program, then build the program with BOOST_ASIO_SEPARATE_COMPILATION defined in the project/compiler settings. Alternatively, BOOST_ASIO_DYN_LINK may be defined to build a separately-compiled Boost.Asio as part of a shared library.

If using Boost.Asio's SSL support, you will also need to add #include <boost/asio/ssl/impl/src.hpp>.


The macros listed in the table below may be used to control the behaviour of Boost.Asio.




Enables Boost.Asio's buffer debugging support, which can help identify when invalid buffers are used in read or write operations (e.g. if a std::string object being written is destroyed before the write operation completes).

When using Microsoft Visual C++ 11.0 or later, this macro is defined automatically if the compiler's iterator debugging support is enabled, unless BOOST_ASIO_DISABLE_BUFFER_DEBUGGING has been defined.

When using g++, this macro is defined automatically if standard library debugging is enabled (_GLIBCXX_DEBUG is defined), unless BOOST_ASIO_DISABLE_BUFFER_DEBUGGING has been defined.


Explictly disables Boost.Asio's buffer debugging support.


Explicitly disables /dev/poll support on Solaris, forcing the use of a select-based implementation.


Explicitly disables epoll support on Linux, forcing the use of a select-based implementation.


Explicitly disables eventfd support on Linux, forcing the use of a pipe to interrupt blocked epoll/select system calls.


Explicitly disables kqueue support on macOS and BSD variants, forcing the use of a select-based implementation.


Explicitly disables I/O completion ports support on Windows, forcing the use of a select-based implementation.


Explicitly disables Boost.Asio's threading support, independent of whether or not Boost as a whole supports threads.


By default, Boost.Asio will automatically define WIN32_LEAN_AND_MEAN when compiling for Windows, to minimise the number of Windows SDK header files and features that are included. The presence of BOOST_ASIO_NO_WIN32_LEAN_AND_MEAN prevents WIN32_LEAN_AND_MEAN from being defined.


By default, Boost.Asio will automatically define NOMINMAX when compiling for Windows, to suppress the definition of the min() and max() macros. The presence of BOOST_ASIO_NO_NOMINMAX prevents NOMINMAX from being defined.


When compiling for Windows using Microsoft Visual C++ or Borland C++, Boost.Asio will automatically link in the necessary Windows SDK libraries for sockets support (i.e. ws2_32.lib and mswsock.lib, or ws2.lib when building for Windows CE). The BOOST_ASIO_NO_DEFAULT_LINKED_LIBS macro prevents these libraries from being linked.


Enables use of the CancelIo function on older versions of Windows. If not enabled, calls to cancel() on a socket object will always fail with asio::error::operation_not_supported when run on Windows XP, Windows Server 2003, and earlier versions of Windows. When running on Windows Vista, Windows Server 2008, and later, the CancelIoEx function is always used.

The CancelIo function has two issues that should be considered before enabling its use:

* It will only cancel asynchronous operations that were initiated in the current thread.

* It can appear to complete without error, but the request to cancel the unfinished operations may be silently ignored by the operating system. Whether it works or not seems to depend on the drivers that are installed.

For portable cancellation, consider using one of the following alternatives:

* Disable asio's I/O completion port backend by defining BOOST_ASIO_DISABLE_IOCP.

* Use the socket object's close() function to simultaneously cancel the outstanding operations and close the socket.


Disables uses of the typeid operator in Boost.Asio. Defined automatically if BOOST_NO_TYPEID is defined.


Determines the number of buckets in Boost.Asio's internal hash_map objects. The value should be a comma separated list of prime numbers, in ascending order. The hash_map implementation will automatically increase the number of buckets as the number of elements in the map increases.

Some examples:

* Defining BOOST_ASIO_HASH_MAP_BUCKETS to 1021 means that the hash_map objects will always contain 1021 buckets, irrespective of the number of elements in the map.

* Defining BOOST_ASIO_HASH_MAP_BUCKETS to 53,389,1543 means that the hash_map objects will initially contain 53 buckets. The number of buckets will be increased to 389 and then 1543 as elements are added to the map.

Mailing List

A mailing list specifically for Boost.Asio may be found on Newsgroup access is provided via Gmane.


Users are encouraged to share examples, tips and FAQs on the Boost.Asio wiki, which is located at