{"id":3845,"date":"2024-03-12T01:30:42","date_gmt":"2024-03-11T20:00:42","guid":{"rendered":"https:\/\/cthecosmos.com\/?p=3845"},"modified":"2024-03-12T01:30:42","modified_gmt":"2024-03-11T20:00:42","slug":"common-combinations-and-their-usage-in-c-part-2","status":"publish","type":"post","link":"https:\/\/cthecosmos.com\/?p=3845","title":{"rendered":"Common Combinations and their Usage in C – Part 2"},"content":{"rendered":"\n

Structure of Unions:<\/strong> Whenever you need different data types to be stored in the same memory. Saves memory space and provides flexibility in handling different data types. Ex: Used for HW configuration where each member in the union corresponds to a specific HW configuration, in protocol parsing, each member in the union can be used to perform specific operations such as parsed, processed etc… on the data.

Syntax:<\/strong> <\/p>\n\n\n

\nUnion uni_on1{ \u2026};\nUnion uni_on2{\u2026};\nstruct struct_of_union{\nunion uni_on1 mem1;\nunion uni_on2 mem2;\n};\nStruct struct_of_union a_struct;\nA_struct.mem1.uni_on1 = some_val;\n<\/pre><\/div>\n\n\n
Ex:<\/p>\n\n\n
\nstruct pmop {\nBASEOP\nOP *\u00a0\u00a0\u00a0op_first;\nOP *\u00a0\u00a0\u00a0op_last;\n\n# ifdef USE_ITHREADS\nPADOFFSET\u00a0\u00a0op_pmoffset;\n#else\nOP *\u00a0\u00a0\u00a0op_pmregexp;\n#endif\n\nU32\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0op_pmflags;\n\nunion {\nOP *\u00a0\u00a0\u00a0op_pmreplroot;\nPADOFFSET op_pmtargetoff;\nGV *\u00a0\u00a0\u00a0op_pmtargetgv;\n}\u00a0\u00a0op_pmreplrootu;\n\nunion {\nOP *\u00a0\u00a0\u00a0op_pmreplstart;\n#ifdef USE_ITHREADS\nPADOFFSET op_pmstashoff;\n#else\nHV *\u00a0\u00a0\u00a0op_pmstash;\n#endif\n}\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0op_pmstashstartu;\n\nOP *\u00a0\u00a0\u00a0op_code_list;\n}; \/\/ Used in Perl regular expression engine to represent a pattern match operation.\n<\/pre><\/div>\n\n\n

(\/lib\/x86_64-linux-gnu\/perl\/5.34.0\/CORE\/op.h)


Union of Structures:<\/strong> Used where we need to represent different data types in same memory location. EX: Used in file data strcutures where features such as file size, permission, timestamps are wrapped in a single data structures.

Ex:<\/em><\/strong><\/p>\n\n\n
\nunion fw_cdev_event {\nstruct fw_cdev_event_common\u00a0\u00a0\u00a0\u00a0common;\nstruct fw_cdev_event_bus_reset\u00a0\u00a0\u00a0\u00a0\u00a0bus_reset;\n...\nstruct fw_cdev_event_iso_interrupt_mc\u00a0\u00a0iso_interrupt_mc;\nstruct fw_cdev_event_iso_resource\u00a0\u00a0iso_resource;\nstruct fw_cdev_event_phy_packet\u00a0\u00a0\u00a0\u00a0phy_packet;\n}; \/\/ Used to represent different types of events or messages that can be received or transmitted within the FireWire communication context.\n<\/pre><\/div>\n\n\n

Structure of union of structure:<\/strong> Used to handle different data formats and interpretations on conditions or modes. Ex: Can be seen its usage in linux kernel sub system network.<\/p>\n\n\n
\nstruct __kernel_sockaddr_storage {\nunion {\nstruct {\n__kernel_sa_family_t\u00a0\u00a0\u00a0ss_family;\nchar __data[_K_SS_MAXSIZE - sizeof(unsigned short)];\n};\nvoid *__align; \u00a0\u00a0\u00a0\u00a0\u00a0}; }; (\/\/usr\/include\/linux\/socket.h)\n<\/pre><\/div>\n\n\n

Array of pointers to functions<\/strong>: Used to store and manage collection of different function pointers.
Syntax:<\/em><\/strong><\/p>\n\n\n
\nchar (*fun_ptr_arr[5])(int,char);\nfun_ptr1[0] = some_fun1();\nfun_ptr2[1] = some_fun2();\n<\/pre><\/div>\n\n\n
\"\"<\/figure>\n\n\n\n
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An Article by: <\/strong>Yashwanth Naidu Tikkisetty
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<\/p>\n","protected":false},"excerpt":{"rendered":"
Structure of Unions: Whenever you need different data types to be stored in the same memory. Saves memory space and provides flexibility in handling different data types. Ex: Used for HW configuration where each member in the union corresponds to a specific HW configuration, in protocol parsing, each member in the union can be used […]<\/p>\nRead More Common Combinations and their Usage in C – Part 2<\/span><\/a>","protected":false},"author":120055267,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"_wpas_customize_per_network":false},"categories":[769112296,36985],"tags":[769116859,770034012,20863,196,67544,770034011,1332],"class_list":["post-3845","post","type-post","status-publish","format-standard","hentry","category-c-concepts-hub","category-c-programming","tag-cprogram-2","tag-declaration-reading","tag-pointers","tag-programming","tag-structures","tag-syntax-reading","tag-unions","has-post-thumbnail","fallback-thumbnail"],"aioseo_notices":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_likes_enabled":true,"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p8CiEf-101","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/cthecosmos.com\/index.php?rest_route=\/wp\/v2\/posts\/3845","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cthecosmos.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cthecosmos.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cthecosmos.com\/index.php?rest_route=\/wp\/v2\/users\/120055267"}],"replies":[{"embeddable":true,"href":"https:\/\/cthecosmos.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3845"}],"version-history":[{"count":7,"href":"https:\/\/cthecosmos.com\/index.php?rest_route=\/wp\/v2\/posts\/3845\/revisions"}],"predecessor-version":[{"id":3853,"href":"https:\/\/cthecosmos.com\/index.php?rest_route=\/wp\/v2\/posts\/3845\/revisions\/3853"}],"wp:attachment":[{"href":"https:\/\/cthecosmos.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3845"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cthecosmos.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3845"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cthecosmos.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3845"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}