{"id":1611,"date":"2019-03-16T20:55:01","date_gmt":"2019-03-16T20:55:01","guid":{"rendered":"http:\/\/demensdeum.com\/blog\/?p=1611"},"modified":"2024-12-16T22:32:40","modified_gmt":"2024-12-16T19:32:40","slug":"%d1%81-application-plugins","status":"publish","type":"post","link":"https:\/\/demensdeum.com\/blog\/de\/2019\/03\/16\/%d1%81-application-plugins\/","title":{"rendered":"\u0421++ Application Plugins"},"content":{"rendered":"

In this post I will describe an example of adding functionality to a C ++ application using plugins.<\/span> The practical part of the implementation for Linux is described; the theory can be found at the links at the end of the article.<\/span><\/span><\/p>\r\n

<\/p>\r\n

<\/p>\r\n

<\/p>\r\n

<\/p>\r\n

\"\"<\/a>\r\n
Composition over inheritance!<\/figcaption>\r\n<\/figure>\r\n

<\/p>\r\n

<\/p>\r\n

To begin with, we will write a plugin – a function that we will call:<\/span><\/span><\/p>\r\n

<\/p>\r\n

<\/p>\r\n

\r\n
#include \"iostream\"<\/span>\r\n\r\nusing<\/span> namespace<\/span> std;\r\n\r\nextern<\/span> \"C\"<\/span> void<\/span> extensionEntryPoint() {\r\n\tcout <<<\/span> \"Extension entry point called\"<\/span> <<<\/span> endl;\r\n};\r\n<\/pre>\r\n<\/div>\r\n
<\/p>\r\n
Next, we will build the plugin as a dynamic library “extension.so”, which we will connect in the future:<\/span><\/span>
clang++ -shared -fPIC extension.cpp -o extension.so<\/strong><\/p>\r\n
<\/p>\r\n
<\/p>\r\n
Next we write the main application that will load the file “extension.so”, look for a pointer to the function “extensionEntryPoint” there, and call it, typing errors if necessary<\/span><\/span>:<\/p>\r\n
<\/p>\r\n
<\/p>\r\n
\r\n
#include \"iostream\"<\/span>\r\n#include \"dlfcn.h\"<\/span>\r\n\r\nusing<\/span> namespace<\/span> std;\r\n\r\ntypedef<\/span> void<\/span> (*<\/span>VoidFunctionPointer)();\t\r\n\r\nint<\/span> main<\/span> (int<\/span> argc, char<\/span> *<\/span>argv[]) {\r\n\r\n\tcout <<<\/span> \"C++ Plugins Example\"<\/span> <<<\/span> endl;\r\n\r\n\tauto<\/span> extensionHandle =<\/span> dlopen(\".\/extension.so\"<\/span>, RTLD_LAZY);\r\n\tif<\/span> (!<\/span>extensionHandle) {\r\n\t\tstring errorString =<\/span> dlerror();\r\n\t\tthrow<\/span> runtime_error(errorString);\r\n\t}\r\n\r\n\tauto<\/span> functionPointer =<\/span> VoidFunctionPointer();\r\n\tfunctionPointer =<\/span> (VoidFunctionPointer) dlsym(extensionHandle, \"extensionEntryPoint\"<\/span>);\r\n\tauto<\/span> dlsymError =<\/span> dlerror();\r\n \tif<\/span> (dlsymError) {\r\n\t\tstring errorString =<\/span> dlerror();\r\n\t\tthrow<\/span> runtime_error(errorString);\r\n \t}\r\n\r\n\tfunctionPointer();\r\n\r\n\texit(0<\/span>);\r\n} \r\n<\/pre>\r\n<\/div>\r\n
<\/p>\r\n
The dlopen function returns a handler for working with a dynamic library;<\/span> dlsym function returns a pointer to the required function by string;<\/span> dlerror contains a pointer to the string with the error text, if any.<\/span><\/span><\/p>\r\n
<\/p>\r\n
<\/p>\r\n
Next, build the main application, copy the file of the dynamic library in the folder with it and run.<\/span> The output should be the “Extension entry point called”<\/strong><\/span><\/span>
<\/strong><\/p>\r\n
<\/p>\r\n
<\/p>\r\n
\r\n
Difficult moments include the lack of a single standard for working with dynamic libraries, because of this there is a need to export the function to a relatively global scope with extern C<\/strong>;<\/span> the difference in working with different operating systems associated with this subtlety of work;<\/span> the lack of a C ++ interface to implement OOP approach to working with dynamic libraries, however, there are open-source wrappers, for example m-renaud\/libdlibxx<\/a>
<\/span><\/span><\/div>\r\n<\/div>\r\n
Example Source Code<\/h2>\r\n
<\/p>\r\n
<\/p>\r\n
https:\/\/gitlab.com\/demensdeum\/cpppluginsexample<\/a><\/p>\r\n
<\/p>\r\n
<\/p>\r\n
Documents<\/h2>\r\n
<\/p>\r\n
<\/p>\r\n
http:\/\/man7.org\/linux\/man-pages\/man3\/dlopen.3.htm<\/a>
https:\/\/gist.github.com\/tailriver\/30bf0c943325330b7b6a<\/a>
https:\/\/stackoverflow.com\/questions\/840501\/how-do-function-pointers-in-c-work<\/a><\/p>\r\n
<\/p>","protected":false},"excerpt":{"rendered":"
In this post I will describe an example of adding functionality to a C ++ application using plugins. The practical part of the implementation for Linux is described; the theory can be found at the links at the end of the article. Composition over inheritance! To begin with, we will write a plugin – aContinue reading “\u0421++ Application Plugins”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[61,52],"tags":[],"class_list":["post-1611","post","type-post","status-publish","format-standard","hentry","category-techie","category-tutorials","entry"],"translation":{"provider":"WPGlobus","version":"3.0.2","language":"de","enabled_languages":["en","ru","zh","de","fr","ja","pt"],"languages":{"en":{"title":true,"content":true,"excerpt":false},"ru":{"title":true,"content":true,"excerpt":false},"zh":{"title":false,"content":false,"excerpt":false},"de":{"title":false,"content":false,"excerpt":false},"fr":{"title":false,"content":false,"excerpt":false},"ja":{"title":false,"content":false,"excerpt":false},"pt":{"title":false,"content":false,"excerpt":false}}},"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/posts\/1611","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/comments?post=1611"}],"version-history":[{"count":26,"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/posts\/1611\/revisions"}],"predecessor-version":[{"id":1691,"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/posts\/1611\/revisions\/1691"}],"wp:attachment":[{"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/media?parent=1611"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/categories?post=1611"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/de\/wp-json\/wp\/v2\/tags?post=1611"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}