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:herb: Expat library: Fast streaming XML parser written in C99; in the process of migrating from SourceForge to GitHub

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Expat, Release 2.4.3

This is Expat, a C library for parsing XML, started by James Clark in 1997. Expat is a stream-oriented XML parser. This means that you register handlers with the parser before starting the parse. These handlers are called when the parser discovers the associated structures in the document being parsed. A start tag is an example of the kind of structures for which you may register handlers.

Expat supports the following compilers:

  • GNU GCC >=4.5
  • LLVM Clang >=3.5
  • Microsoft Visual Studio >=15.0/2017 (rolling
    ${today} minus 5 years

Windows users can use the

download, which includes both pre-compiled libraries and executables, and source code for developers.

Expat is free software. You may copy, distribute, and modify it under the terms of the License contained in the file

distributed with this package. This license is the same as the MIT/X Consortium license.

Using libexpat in your CMake-Based Project

There are two ways of using libexpat with CMake:

a) Module Mode

This approach leverages CMake's own module


Notice the uppercase

in the following example:
cmake_minimum_required(VERSION 3.0)  # or 3.10, see below

project(hello VERSION 1.0.0)

find_package(EXPAT 2.2.8 MODULE REQUIRED)

add_executable(hello hello.c )

a) for CMake >=3.10 (see CMake's FindEXPAT docs)

target_link_libraries(hello PUBLIC EXPAT::EXPAT)

b) for CMake >=3.0

target_include_directories(hello PRIVATE ${EXPAT_INCLUDE_DIRS}) target_link_libraries(hello PUBLIC ${EXPAT_LIBRARIES})

b) Config Mode

This approach requires files from…

  • libexpat >=2.2.8 where packaging uses the CMake build system or
  • libexpat >=2.3.0 where packaging uses the GNU Autotools build system on Linux or
  • libexpat >=2.4.0 where packaging uses the GNU Autotools build system on macOS or MinGW.

Notice the lowercase

in the following example:
cmake_minimum_required(VERSION 3.0)

project(hello VERSION 1.0.0)

find_package(expat 2.2.8 CONFIG REQUIRED char dtd ns)

add_executable(hello hello.c )

target_link_libraries(hello PUBLIC expat::expat)

Building from a Git Clone

If you are building Expat from a check-out from the Git repository, you need to run a script that generates the configure script using the GNU autoconf and libtool tools. To do this, you need to have autoconf 2.58 or newer. Run the script like this:


Once this has been done, follow the same instructions as for building from a source distribution.

Building from a Source Distribution

a) Building with the configure script (i.e. GNU Autotools)

To build Expat from a source distribution, you first run the configuration shell script in the top level distribution directory:


There are many options which you may provide to configure (which you can discover by running configure with the

option). But the one of most interest is the one that sets the installation directory. By default, the configure script will set things up to install libexpat into
, and
. If, for example, you'd prefer to install into
, and
, you can tell
about that with:
./configure --prefix=/home/me/mystuff

Another interesting option is to enable 64-bit integer support for line and column numbers and the over-all byte index:


However, such a modification would be a breaking change to the ABI and is therefore not recommended for general use — e.g. as part of a Linux distribution — but rather for builds with special requirements.

After running the configure script, the

command will build things and
make install
will install things into their proper location. Have a look at the
to learn about additional
options. Note that you need to have write permission into the directories into which things will be installed.

If you are interested in building Expat to provide document information in UTF-16 encoding rather than the default UTF-8, follow these instructions (after having run

make distclean
). Please note that we configure with
as xmlwf does not support this mode of compilation (yet):
  1. Mass-patch
    files to use
    for a library name:
    find -name -exec sed
       -e 's,libexpat\.la,,'
       -e 's,libexpat_la,libexpatw_la,'
       -i {} +
  2. Run

    to re-write
  3. For UTF-16 output as unsigned short (and version/error strings as char), run:

    ./configure CPPFLAGS=-DXML_UNICODE --without-xmlwf

    For UTF-16 output as
    (incl. version/error strings), run:
    ./configure CFLAGS="-g -O2 -fshort-wchar" CPPFLAGS=-DXML_UNICODE_WCHAR_T

    Note: The latter requires libc compiled with
    , as well.
  4. Run

    (which excludes xmlwf).
  5. Run

    make install
    (again, excludes xmlwf).


is supported. It works as follows:
make install DESTDIR=/path/to/image

overrides the in-makefile set

, because variable-setting priority is
  1. commandline
  2. in-makefile
  3. environment

Note: This only applies to the Expat library itself, building UTF-16 versions of xmlwf and the tests is currently not supported.

When using Expat with a project using autoconf for configuration, you can use the probing macro in

to determine how to include Expat. See the comments at the top of that file for more information.

A reference manual is available in the file

in this distribution.

b) Building with CMake

The CMake build system is still experimental and may replace the primary build system based on GNU Autotools at some point when it is ready.

Available Options

For an idea of the available (non-advanced) options for building with CMake:

# rm -f CMakeCache.txt ; cmake -D_EXPAT_HELP=ON -LH . | grep -B1 ':.*=' | sed 's,^--$,,'
// Choose the type of build, options are: None Debug Release RelWithDebInfo MinSizeRel ...

// Install path prefix, prepended onto install directories. CMAKE_INSTALL_PREFIX:PATH=/usr/local

// Path to a program. DOCBOOK_TO_MAN:FILEPATH=/usr/bin/docbook2x-man

// build man page for xmlwf EXPAT_BUILD_DOCS:BOOL=ON

// build the examples for expat library EXPAT_BUILD_EXAMPLES:BOOL=ON

// build fuzzers for the expat library EXPAT_BUILD_FUZZERS:BOOL=OFF

// build pkg-config file EXPAT_BUILD_PKGCONFIG:BOOL=ON

// build the tests for expat library EXPAT_BUILD_TESTS:BOOL=ON

// build the xmlwf tool for expat library EXPAT_BUILD_TOOLS:BOOL=ON

// Character type to use (char|ushort|wchar_t) [default=char] EXPAT_CHAR_TYPE:STRING=char

// install expat files in cmake install target EXPAT_ENABLE_INSTALL:BOOL=ON

// Use /MT flag (static CRT) when compiling in MSVC EXPAT_MSVC_STATIC_CRT:BOOL=OFF

// build fuzzers via ossfuzz for the expat library EXPAT_OSSFUZZ_BUILD:BOOL=OFF

// build a shared expat library EXPAT_SHARED_LIBS:BOOL=ON

// Treat all compiler warnings as errors EXPAT_WARNINGS_AS_ERRORS:BOOL=OFF

// Make use of getrandom function (ON|OFF|AUTO) [default=AUTO] EXPAT_WITH_GETRANDOM:STRING=AUTO

// utilize libbsd (for arc4random_buf) EXPAT_WITH_LIBBSD:BOOL=OFF

// Make use of syscall SYS_getrandom (ON|OFF|AUTO) [default=AUTO] EXPAT_WITH_SYS_GETRANDOM:STRING=AUTO

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