In this post, I will introduce custom deleters when using C++ Use the following snippets. Note the fourth case, where a The result will be <\/p>\n Summary In this post, I will introduce custom deleters when using C++ std::shared_ptr and std::unique_ptr. Conclusion Use the following snippets. Note the fourth case, where a unique_ptr with custom deleter will not pass the deleter to the shared_ptr when using release(). class OldThing { public: ~OldThing() { if (allocated_) { std::cout << "MEMORY LEAK!" <<…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,5],"tags":[],"class_list":["post-754","post","type-post","status-publish","format-standard","hentry","category-c","category-proglang"],"_links":{"self":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/754","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/comments?post=754"}],"version-history":[{"count":1,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/754\/revisions"}],"predecessor-version":[{"id":755,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/754\/revisions\/755"}],"wp:attachment":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/media?parent=754"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/categories?post=754"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/tags?post=754"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}std::shared_ptr<\/code> and std::unique_ptr<\/code>. <\/p>\nConclusion<\/h2>\n
unique_ptr<\/code> with custom deleter will not pass the deleter to the shared_ptr<\/code> when using release()<\/code>.<\/p>\nclass OldThing {\n public:\n ~OldThing() \n {\n if (allocated_) {\n std::cout << "MEMORY LEAK!" << std::endl;\n }\n }\n void Deallocate()\n {\n std::cout << "Deallocate called." << std::endl;\n allocated_ = false;\n }\n private:\n bool allocated_{ true };\n};\nint main() { \n {\n OldThing oldThing;\n \/\/ oldThing going out of scope causes a "memory leak"\n }\n\n {\n \/\/ shared_ptr's constuctor handles the deleter\n std::shared_ptr<OldThing> p(new OldThing, \n [] (OldThing* ot) {\n ot->Deallocate();\n delete ot;\n }\n );\n }\n\n {\n \/\/ We need to include the deleter's type in the template parameters:\n std::unique_ptr<OldThing, void(*)(OldThing*)> p(new OldThing, \n [] (OldThing* ot) {\n ot->Deallocate();\n delete ot;\n }\n );\n }\n\n {\n \/\/ !!! memory leak!!!\n std::unique_ptr<OldThing, void(*)(OldThing*)> p(new OldThing, \n [] (OldThing* ot) {\n ot->Deallocate();\n delete ot;\n }\n );\n auto p_ = std::shared_ptr<OldThing>(p.release());\n }\n\n {\n \/\/ works, shared_ptr receives the deleter from unique_ptr\n std::unique_ptr<OldThing, void(*)(OldThing*)> p(new OldThing, \n [] (OldThing* ot) {\n ot->Deallocate();\n delete ot;\n }\n );\n std::shared_ptr<OldThing> p_ = std::move(p);\n }\n\n return 0;\n}<\/code><\/pre>\nMEMORY LEAK! \nDeallocate called. \nDeallocate called. \nMEMORY LEAK! \nDeallocate called. <\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"