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[/
Copyright 2014 Renato Tegon Forti, Antony Polukhin.
Copyright Antony Polukhin, 2015-2025.
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
/]
[section:getting_started Getting started]
Boost.DLL is a header only library. To start with the library you only need to include `<boost/dll.hpp>` header. After that you are free to import and export functions and variables.
`boost::dll::import*` functions require linking with `boost_filesystem` and `boost_system` libraries, along with some platform specific dynamic load libraries like `dl`. With CMake
that burden goes away as `find_package(Boost COMPONENTS dll)` provides a `Boost::dll` target that manages the dependencies to other libraries.
If you want to load a library, just construct [classref boost::dll::shared_library] class with a path to the library as a parameter:
```
boost::dll::shared_library lib("/test/boost/application/libtest_library.so");
```
Now you can easily import symbols from that library using the `get` and `get_alias` member functions:
```
int plugin_constant = lib.get<const int>("integer_variable");
auto function_ptr = lib.get<int()>("function_returning_int");
int& i = lib.get_alias<int>("alias_to_int_variable");
```
In case of `boost::dll::shared_library` it is safe to use imported symbols only until `boost::dll::shared_library`
instance is not destroyed.
Query libraries using [classref boost::dll::library_info] and get symbol infos using [funcref boost::dll::symbol_location],
[funcref boost::dll::this_line_location] and [funcref boost::dll::program_location].
For importing a single function or variable you may use a following one liners:
[import ../example/getting_started.cpp]
[import ../example/getting_started_library.cpp]
```
using namespace boost;
// `extern "C"` - specifies C linkage: forces the compiler to export function/variable by a pretty (unmangled) C name.
#define API extern "C" BOOST_SYMBOL_EXPORT
```
[table:starting
[[ Import (code that uses DLL/DSL): ] [ Export (DLL/DSL sources): ] [ Functions description: ]]
[
[ [getting_started_imports_cpp11_function] ]
[ [getting_started_exports_cpp11_function] ]
[ [funcref boost::dll::import import<T>(...)] ]
][
[ [getting_started_imports_cpp_variable] ]
[ [getting_started_exports_cpp_variable] ]
[ [funcref boost::dll::import import<T>(...)] ]
][
[ [getting_started_imports_alias] ]
[ [getting_started_exports_alias] ]
[
[funcref boost::dll::import_alias import_alias<T>(...)]
[macroref BOOST_DLL_ALIAS]
]
][/
[ [getting_started_imports_c_function] ]
[ [getting_started_exports_c_function] ]
[ [funcref boost::dll::import import<T>(...) ] ]
/][/
[ [getting_started_imports_c_variable] ]
[ [getting_started_exports_c_variable] ]
[ [funcref boost::dll::import import<T>(...) ] ]
/]]
It is safe to use imported variable or function because the variables returned from [funcref boost::dll::import import<T>(...)] and [funcref boost::dll::import_alias import_alias<T>(...)] functions
internally hold a reference to the shared library.
[macroref BOOST_SYMBOL_EXPORT] is just a macro from Boost.Config that expands into the `__declspec(dllexport)` or `__attribute__((visibility("default")))`. You are free to use your own macro for exports.
[note On Linux/POSIX/MacOS link with library "dl". "-fvisibility=hidden" flag is also recommended.]
[endsect]
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