{"id":18379,"date":"2025-02-18T11:03:56","date_gmt":"2025-02-18T11:03:56","guid":{"rendered":"http:\/\/www.max-sperling.bplaced.net\/?p=18379"},"modified":"2025-02-20T13:19:34","modified_gmt":"2025-02-20T13:19:34","slug":"ways-to-pass-values-c","status":"publish","type":"post","link":"http:\/\/www.max-sperling.bplaced.net\/?p=18379","title":{"rendered":"How to pass arguments (C++)"},"content":{"rendered":"

Analysis<\/strong><\/p>\n

\nCode \u25bc<\/summary>\n
\r\n#include <iostream>\r\n#include <string>\r\n\r\nclass Foo {\r\npublic:\r\n    std::string bar;\r\n\r\n    Foo(const std::string& d) : bar(d) {\r\n        std::cout << "Constructor: " << bar << "\\n";\r\n    }\r\n\r\n    Foo(const Foo& other) : bar(other.bar) {\r\n        std::cout << "Copy Constructor: " << bar << "\\n";\r\n    }\r\n\r\n    Foo(Foo&& other) noexcept : bar(std::move(other.bar)) {\r\n        std::cout << "Move Constructor: " << bar << "\\n";\r\n    }\r\n\r\n    Foo& operator=(const Foo& other) {\r\n        std::cout << "Copy Assignment: " << other.bar << "\\n";\r\n        bar = other.bar;\r\n        return *this;\r\n    }\r\n\r\n    Foo& operator=(Foo&& other) noexcept {\r\n        std::cout << "Move Assignment: " << other.bar << "\\n";\r\n        bar = std::move(other.bar);\r\n        return *this;\r\n    }\r\n\r\n    void print() const {\r\n        \/\/ std::cout << "Current content: " << bar << "\\n";\r\n    }\r\n};\r\n\r\nFoo g_foo("bar_0");\r\n\r\nvoid copy_no_store(Foo foo) { foo.print(); }\r\nvoid const_ref_no_store(const Foo& foo) { foo.print(); }\r\nvoid ref_no_store(Foo& foo) { foo.print(); }\r\ntemplate <typename T> void uni_ref_no_store(T&& foo) { foo.print(); }\r\ntemplate <typename T> void const_uni_ref_no_store(const T&& foo) { foo.print(); }\r\n\r\nvoid copy_store(Foo foo) { g_foo = std::move(foo); }\r\nvoid const_ref_store(const Foo& foo) { g_foo = foo; }\r\nvoid ref_store(Foo& foo) { g_foo = foo; }\r\ntemplate <typename T> void uni_ref_store(T&& foo) { g_foo = std::forward<T>(foo); }\r\ntemplate <typename T> void const_uni_ref_store(const T&& foo) { g_foo = std::forward<const T>(foo); }\r\n\r\nvoid run_copy_no_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_1");\r\n    std::cout << "=== lvalue ===\\n";\r\n    copy_no_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    copy_no_store(std::move(foo));\r\n}\r\nvoid run_const_ref_no_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_2");\r\n    std::cout << "=== lvalue ===\\n";\r\n    const_ref_no_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    const_ref_no_store(std::move(foo));\r\n}\r\nvoid run_ref_no_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_3");\r\n    std::cout << "=== lvalue ===\\n";\r\n    ref_no_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    \/\/ref_no_store(std::move(foo));\r\n    std::cout << "not possible\\n";\r\n}\r\nvoid run_uni_ref_no_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_4");\r\n    std::cout << "=== lvalue ===\\n";\r\n    uni_ref_no_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    uni_ref_no_store(std::move(foo));\r\n}\r\nvoid run_const_uni_ref_no_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_5");\r\n    std::cout << "=== lvalue ===\\n";\r\n    \/\/const_uni_ref_no_store(foo);\r\n    std::cout << "not possible\\n";\r\n    std::cout << "=== rvalue ===\\n";\r\n    const_uni_ref_no_store(std::move(foo));\r\n}\r\n\r\nvoid run_copy_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_1");\r\n    std::cout << "=== lvalue ===\\n";\r\n    copy_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    copy_store(std::move(foo));\r\n}\r\nvoid run_const_ref_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_2");\r\n    std::cout << "=== lvalue ===\\n";\r\n    const_ref_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    const_ref_store(std::move(foo));\r\n}\r\nvoid run_ref_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_3");\r\n    std::cout << "=== lvalue ===\\n";\r\n    ref_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    \/\/ref_store(std::move(foo));\r\n    std::cout << "not possible\\n";\r\n}\r\nvoid run_uni_ref_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_4");\r\n    std::cout << "=== lvalue ===\\n";\r\n    uni_ref_store(foo);\r\n    std::cout << "=== rvalue ===\\n";\r\n    uni_ref_store(std::move(foo));\r\n}\r\nvoid run_const_uni_ref_store() {\r\n    std::cout << "\\n" << __func__ << "\\n";\r\n    Foo foo("bar_5");\r\n    std::cout << "=== lvalue ===\\n";\r\n    \/\/const_uni_ref_store(foo);\r\n    std::cout << "not possible\\n";\r\n    std::cout << "=== rvalue ===\\n";\r\n    const_uni_ref_store(std::move(foo));\r\n}\r\n\r\nint main() {\r\n    std::cout << "\\nNot store copy\\n";\r\n    run_copy_no_store();\r\n    run_const_ref_no_store();\r\n    run_ref_no_store();\r\n    run_uni_ref_no_store();\r\n    run_const_uni_ref_no_store();\r\n\r\n    std::cout << "\\nStore copy\\n";\r\n    run_copy_store();\r\n    run_const_ref_store();\r\n    run_ref_store();\r\n    run_uni_ref_store();\r\n    run_const_uni_ref_store();\r\n\r\n    return 0;\r\n}\r\n<\/pre>\n<\/details>\n
\nOutput \u25bc<\/summary>\n
\r\nConstructor: bar_0\r\n\r\nNot store copy\r\n\r\nrun_copy_no_store\r\nConstructor: bar_1\r\n=== lvalue ===\r\nCopy Constructor: bar_1\r\n=== rvalue ===\r\nMove Constructor: bar_1\r\n\r\nrun_const_ref_no_store\r\nConstructor: bar_2\r\n=== lvalue ===\r\n=== rvalue ===\r\n\r\nrun_ref_no_store\r\nConstructor: bar_3\r\n=== lvalue ===\r\n=== rvalue ===\r\nnot possible\r\n\r\nrun_uni_ref_no_store\r\nConstructor: bar_4\r\n=== lvalue ===\r\n=== rvalue ===\r\n\r\nrun_const_uni_ref_no_store\r\nConstructor: bar_5\r\n=== lvalue ===\r\nnot possible\r\n=== rvalue ===\r\n\r\nStore copy\r\n\r\nrun_copy_store\r\nConstructor: bar_1\r\n=== lvalue ===\r\nCopy Constructor: bar_1\r\nMove Assignment: bar_1\r\n=== rvalue ===\r\nMove Constructor: bar_1\r\nMove Assignment: bar_1\r\n\r\nrun_const_ref_store\r\nConstructor: bar_2\r\n=== lvalue ===\r\nCopy Assignment: bar_2\r\n=== rvalue ===\r\nCopy Assignment: bar_2\r\n\r\nrun_ref_store\r\nConstructor: bar_3\r\n=== lvalue ===\r\nCopy Assignment: bar_3\r\n=== rvalue ===\r\nnot possible\r\n\r\nrun_uni_ref_store\r\nConstructor: bar_4\r\n=== lvalue ===\r\nCopy Assignment: bar_4\r\n=== rvalue ===\r\nMove Assignment: bar_4\r\n\r\nrun_const_uni_ref_store\r\nConstructor: bar_5\r\n=== lvalue ===\r\nnot possible\r\n=== rvalue ===\r\nCopy Assignment: bar_5\r\n<\/pre>\n<\/details>\n
Not store copy<\/p>\n\n\n\n\n\n\n\n\n  <\/colgroup>\n\n\n\n
<\/th>\ncopy_no_store<\/th>\nconst_ref_no_store<\/th>\nref_no_store<\/th>\nuni_ref_no_store<\/th>\nconst_uni_ref_no_store<\/th>\n<\/tr>\n
lvalue<\/th>\n1 Copy<\/td>\n–<\/td>\n–<\/td>\n–<\/td>\nNot possible<\/td>\n<\/tr>\n
rvalue<\/th>\n1 Move<\/td>\n–<\/td>\nNot possible<\/td>\n–<\/td>\n–<\/td>\n<\/tr>\n<\/table>\n
Store copy<\/p>\n\n\n\n\n\n\n\n\n  <\/colgroup>\n\n\n\n
<\/th>\ncopy_store<\/th>\nconst_ref_store<\/th>\nref_store<\/th>\nuni_ref_store<\/th>\nconst_uni_ref_store<\/th>\n<\/tr>\n
lvalue<\/th>\n1 Copy
1 Move<\/td>\n		1 Copy<\/td>\n1 Copy<\/td>\n1 Copy<\/td>\nNot possible<\/td>\n<\/tr>\n
rvalue<\/th>\n2 Moves<\/td>\n1 Copy<\/td>\nNot possible<\/td>\n1 Move<\/td>\n1 Copy<\/td>\n<\/tr>\n<\/table>\n<\/details>\n
\n
Result<\/strong><\/p>\n
Decision table<\/p>\n\n\n\n\n\n\n\n\n\n\n
Small object?<\/th>\nModify original?<\/th>\nStore copy?<\/th>\nResult<\/th>\n<\/tr>\n
Yes<\/td>\nYes<\/td>\nYes<\/td>\nuni_ref_store<\/th>\n<\/tr>\n
Yes<\/td>\nYes<\/td>\nNo<\/td>\nuni_ref_no_store<\/th>\n<\/tr>\n
Yes<\/td>\nNo<\/td>\nYes<\/td>\ncopy_store<\/th>\n<\/tr>\n
Yes<\/td>\nNo<\/td>\nNo<\/td>\ncopy_no_store<\/th>\n<\/tr>\n
No<\/td>\nYes<\/td>\nYes<\/td>\nuni_ref_store<\/th>\n<\/tr>\n
No<\/td>\nYes<\/td>\nNo<\/td>\nuni_ref_no_store<\/th>\n<\/tr>\n
No<\/td>\nNo<\/td>\nYes<\/td>\ncopy_store<\/th>\n<\/tr>\n
No<\/td>\nNo<\/td>\nNo<\/td>\nconst_ref_no_store<\/th>\n<\/tr>\n<\/table>\n
\n
Further information: When and how to pass smart pointer (C++)<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
Analysis Code \u25bc Output \u25bc Constructor: bar_0 Not store copy run_copy_no_store Constructor: bar_1 === lvalue === Copy Constructor: bar_1 ===<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false},"categories":[27],"tags":[],"_links":{"self":[{"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=\/wp\/v2\/posts\/18379"}],"collection":[{"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=18379"}],"version-history":[{"count":50,"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=\/wp\/v2\/posts\/18379\/revisions"}],"predecessor-version":[{"id":18441,"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=\/wp\/v2\/posts\/18379\/revisions\/18441"}],"wp:attachment":[{"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=18379"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=18379"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.max-sperling.bplaced.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=18379"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}