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114 lines
4.8 KiB
ReStructuredText
114 lines
4.8 KiB
ReStructuredText
.. _using-library:
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Using the qpdf Library
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======================
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.. _using.from-cxx:
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Using qpdf from C++
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-------------------
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The source tree for the qpdf package has an
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:file:`examples` directory that contains a few
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example programs. The :file:`libqpdf/QPDFJob.cc` source
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file also serves as a useful example since it exercises almost all of
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the qpdf library's public interface. The best source of documentation on
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the library itself is reading comments in
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:file:`include/qpdf/QPDF.hh`,
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:file:`include/qpdf/QPDFWriter.hh`, and
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:file:`include/qpdf/QPDFObjectHandle.hh`.
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All header files are installed in the
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:file:`include/qpdf` directory. It is recommend that
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you use ``#include <qpdf/QPDF.hh>`` rather than adding
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:file:`include/qpdf` to your include path.
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qpdf installs a ``pkg-config`` configuration with package name
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``libqpdf`` and a ``cmake`` configuration with package name ``qpdf``.
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The ``libqpdf`` target is exported in the ``qpdf::`` namespace. The
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following is an example of a :file:`CMakeLists.txt` file for a
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single-file executable that links with qpdf:
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.. code-block:: cmake
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cmake_minimum_required(VERSION 3.16)
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project(some-application LANGUAGES CXX)
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find_package(qpdf)
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add_executable(some-application some-application.cc)
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target_link_libraries(some-application qpdf::libqpdf)
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The qpdf library is safe to use in a multithreaded program, but no
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individual ``qpdf`` object instance (including ``QPDF``,
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``QPDFObjectHandle``, or ``QPDFWriter``) can be used in more than one
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thread at a time. Multiple threads may simultaneously work with
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different instances of these and all other qpdf objects.
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.. _using.other-languages:
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Using qpdf from other languages
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-------------------------------
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The qpdf library is implemented in C++, which makes it hard to use
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directly in other languages. There are a few things that can help.
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"C"
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The qpdf library includes a "C" language interface that provides a
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subset of the overall capabilities. The header file
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:file:`qpdf/qpdf-c.h` includes information about
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its use. As long as you use a C++ linker, you can link C programs
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with qpdf and use the C API. For languages that can directly load
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methods from a shared library, the C API can also be useful. People
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have reported success using the C API from other languages on Windows
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by directly calling functions in the DLL.
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Python
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A Python module called
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`pikepdf <https://pypi.org/project/pikepdf/>`__ provides a clean and
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highly functional set of Python bindings to the qpdf library. Using
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pikepdf, you can work with PDF files in a natural way and combine
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qpdf's capabilities with other functionality provided by Python's
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rich standard library and available modules.
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Other Languages
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Starting with version 11.0.0, the :command:`qpdf`
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command-line tool can produce an unambiguous JSON representation of
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a PDF file and can also create or update PDF files using this JSON
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representation. qpdf versions from 8.3.0 through 10.6.3 had a more
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limited JSON output format. The qpdf JSON format makes it possible
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to inspect and modify the structure of a PDF file down to the
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object level from the command-line or from any language that can
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handle JSON data. Please see :ref:`json` for details.
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Wrappers
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The `qpdf Wiki <https://github.com/qpdf/qpdf/wiki>`__ contains a
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list of `Wrappers around qpdf
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<https://github.com/qpdf/qpdf/wiki/qpdf-Wrappers>`__. These may
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have varying degrees of functionality or completeness. If you know
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of (or have written) a wrapper that you'd like include, open an
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issue at https://github.com/qpdf/qpdf/issues/new and ask for it to
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be added to the list.
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.. _unicode-files:
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A Note About Unicode File Names
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-------------------------------
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When strings are passed to qpdf library routines either as ``char*`` or
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as ``std::string``, they are treated as byte arrays except where
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otherwise noted. When Unicode is desired, qpdf wants UTF-8 unless
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otherwise noted in comments in header files. In modern UNIX/Linux
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environments, this generally does the right thing. In Windows, it's a
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bit more complicated. Starting in qpdf 8.4.0, passwords that contain
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Unicode characters are handled much better, and starting in qpdf 8.4.1,
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the library attempts to properly handle Unicode characters in filenames.
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In particular, in Windows, if a UTF-8 encoded string is used as a
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filename in either ``QPDF`` or ``QPDFWriter``, it is internally
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converted to ``wchar_t*``, and Unicode-aware Windows APIs are used. As
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such, qpdf will generally operate properly on files with non-ASCII
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characters in their names as long as the filenames are UTF-8 encoded for
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passing into the qpdf library API, but there are still some rough edges,
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such as the encoding of the filenames in error messages or CLI output
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messages. Patches or bug reports are welcome for any continuing issues
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with Unicode file names in Windows.
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