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Installing-and-Using.md

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Installing and Using

Contents

Requirements

The PEGTL requires a C++17-capable compiler, e.g. one of

  • GCC 8
  • Clang 5
  • Visual Studio 2017

with (on Unix)

  • libstdc++ 8
  • libc++ 7

on either

  • Linux
  • macOS
  • Windows

It requires C++17, e.g. using the --std=c++17 compiler switch. Using newer versions of the C++ standard is supported.

Note that using libstdc++ 8 requires linking with -lstdc++fs.

Larger projects will frequently require the /bigobj option when compiling with Visual Studio on Windows.

It should also work with other C++17 compilers on other Unix systems (or any sufficiently compatible platform).

The PEGTL is written with an emphasis on clean code and is compatible with the -pedantic, -Wall, -Wextra and -Werror compiler switches.

Installation Packages

Installation packages are available from several package managers. Note that some of the listed packages are not updated regularly.

Packaging status

Using Conan

Download

You can download and install the PEGTL using the Conan package manager:

conan install taocpp-pegtl/<version>@

where <version> is the version of the PEGTL you want to use.

The taocpp-pegtl package in Conan is kept up to date by Conan team members and community contributors. If the version is out-of-date, please create an issue or pull request on the Conan Center Index repository.

For more options and ways to use Conan, please refer to the Conan documentation.

Using CMake

CMake Installation

The PEGTL can be built and installed using CMake, e.g.

$ mkdir build
$ cd build
$ cmake ..
$ make
$ make install

The above will install the PEGTL into the standard installation path on a UNIX system, e.g. /usr/local/include/. To change the installation path, use:

$ cmake .. -DCMAKE_INSTALL_PREFIX=../install

in the above.

find_package

Installation creates a pegtl-config.cmake which allows CMake projects to find the PEGTL using find_package:

find_package(pegtl)

This exports the taocpp::pegtl target which can be linked against any other target. Linking against taocpp:pegtl automatically sets the include directories and required flags for C++17 or later. For example:

add_executable(myexe mysources...)
target_link_libraries(myexe PRIVATE taocpp::pegtl)

add_subdirectory

The PEGTL can also be added as a dependency with add_subdirectory:

add_subdirectory(path/to/PEGTL)

This also exports the taocpp::pegtl target which can be linked against any other target just as with the installation case.

Due to the global nature of CMake targets the target pegtl is also defined, but only taocpp::pegtl should be used for consistency.

If PEGTL_BUILD_TESTS is true then the test targets, pegtl-test-*, are also defined and their corresponding tests registered with add_test. If PEGTL_BUILD_EXAMPLES is true then the example targets, pegtl-example-*, are also defined.

Mixing find_package and add_subdirectory

With the advent of improved methods of managing dependencies (such as Conan, CMake FetchContent), multiple package inclusion methods needs to be able to co-exist.

If PEGTL was first included with find_package then subsequent calls to add_subdirectory(path/to/PEGTL) will skip over the body of the CMakeLists.txt and use the installed package if the version matches. If the version does not match a fatal error will be signalled.

If PEGTL was first included with add_subdirectory then a dummy pegtl-config.cmake is created and pegtl_DIR is set. Subsequent calls to find_package(pegtl) will then use the already added package if the version matches. If the version does not match a fatal error will be signalled.

Since CMake targets are global, there exists no way for a CMake project to use two different versions of PEGTL simultaneously and signalling a fatal error becomes the only practical way of handling the inclusion of multiple different PEGTL versions.

For more options and ways to use CMake, please refer to the CMake documentation.

Manual Installation

Since the PEGTL is a header-only library, it doesn't itself need to be compiled. In terms of installation for use in other projects, the following steps are required.

  • The include/ directory and the LICENSE file should be copied somewhere, e.g.

    • to /usr/local/include/ in order to use it system-wide, or
    • to some appropriate directory within your project,

  • A compatible compiler with appropriate compiler switches must be used.

  • The compiler search-path for include files must include (no pun intended) the directory that contains the tao/pegtl/ directory and tao/pegtl.hpp header.

The Makefile and .cpp-files included in the PEGTL distribution archive serve as practical examples on how to develop grammars and applications with the PEGTL. Invoking make in the main PEGTL directory builds all included example programs and builds and runs all unit tests.

The Makefile is as simple as possible, but should manage to build the examples and unit tests on Linux with GCC and on macOS with Clang (as supplied by Apple). When running into problems using other combinations, please consult the Makefile for customising the build process.

Embedding the PEGTL

When embedding the PEGTL into other projects, several problems may come up due to the nature of C++ header-only libraries. Depending on the scenario, there are various ways of working around these problems.

Embedding in Binaries

When creating application binaries, i.e. executable files, the PEGTL source tree can be copied to some subdirectory in the application source, and added to the compiler's or project's include paths. No further changes are needed.

Embedding in Libraries

When writing libraries with the PEGTL, it has to be ensured that applications that are built with these libraries, and that themselves use the PEGTL, do not violate the One Definition Rule (ODR) as would be the case when application and libraries contain different versions of the PEGTL.

Since the PEGTL does not guarantee ABI compatibility, not even across minor or patch releases, libraries have to ensure that the symbols for the PEGTL they include differ from those of the applications that use them.

This can be achieved by changing the macro TAO_PEGTL_NAMESPACE which, by default, is set to tao::pegtl. To change the namespace, simply define TAO_PEGTL_NAMESPACE to a unique name before including the PEGTL, for example:

#define TAO_PEGTL_NAMESPACE mylib::pegtl

#include <tao/pegtl.hpp>
#include <tao/contrib/json.hpp>

int main( int argc, char* argv[] )
{
   if( argc > 1 ) {
     mylib::pegtl::argv_input in( argv, 1 );
     mylib::pegtl::parse< mylib::pegtl::json::text >( in );
   }
}

Embedding in Library Interfaces

When PEGTL headers are included in headers of a library, setting the namespace to a unique name via TAO_PEGTL_NAMESPACE is not sufficient since both the application's and the library's copy of the PEGTL use the same macro names.

In this case it is necessary to change the prefix of all macros of the embedded PEGTL from TAO_PEGTL_ to another unique string in order to prevent macros from clashing. In a Unix-shell, the following command will achieve this:

$ sed -i 's/TAO_PEGTL_/MYLIB_PEGTL_/g' $(find -name '[^.]*.[hc]pp')

The above command needs to run from the top-level directory of the embedded PEGTL. Additionally, MYLIB_PEGTL_NAMESPACE needs to be set as explained above; alternatively include/tao/pegtl/config.hpp can be directly modified.

A practical example of how the result looks like can be found in our own header-only JSON library taoJSON.

Single Header Version

You can generate a single-header-version of the PEGTL with the included Makefile. In a Unix-shell, the following command will achieve this:

$ make amalgamate

The above will generate a build/amalgamated/pegtl.hpp which will consist of the headers tao/pegtl.hpp, their dependencies, and all headers in tao/pegtl/contrib/ except for the headers in tao/pegtl/contrib/icu/.

Copyright (c) 2014-2020 Dr. Colin Hirsch and Daniel Frey