{"id":769,"date":"2009-03-10T13:16:48","date_gmt":"2009-03-10T18:16:48","guid":{"rendered":"http:\/\/bitpost.com\/news\/?p=769"},"modified":"2011-04-06T18:21:06","modified_gmt":"2011-04-06T23:21:06","slug":"my-first-c-vs-c99-collision","status":"publish","type":"post","link":"https:\/\/bitpost.com\/news\/2009\/my-first-c-vs-c99-collision\/","title":{"rendered":"My first C++ vs. C99 collision"},"content":{"rendered":"

Recently, I found myself kind of annoyed by the fact that I couldn’t use the same “initialization” syntax to directly set the values of an existing structure. Extremely trivial, but it bugs me. Is there really a good reason for this limitation?<\/p>\n

\ttypedef struct\r\n\t{\r\n\t    int x;\r\n\t    int y;\r\n\r\n\t} Doh;\r\n\r\n    Doh doh = { 1, 2 };\r\n\r\n    \/\/ You can't directly re-assign in one step, bummer.\r\n    \/\/ doh = { 3, 4 };\r\n\r\n    \/\/ You need a second struct to use the same syntax.  Yuck.\r\n    Doh d2 = { 3, 4 };   \r\n    doh = d2;\r\n\r\n    \/\/ Or just do it longhand.  Also yuck.\r\n    doh.x = 5;\r\n    doh.y = 6;\r\n<\/code><\/pre>\n
So I dug around to see if there was anything I was missing, and I found designated initializers<\/strong>, the new initialization method available in C99.  It doesn’t allow me to directly assign values to an existing structure, but it is interesting:<\/p>\n
\tDoh doh_set = { \r\n\t    .x = 4,\r\n\t    .y = 3\r\n\t};\r\n\tDoh doh_set2 = { \r\n\t    .y = 3, \r\n\t    .x = 4 \r\n\t};\r\n\tDoh doh_set3 = { \r\n\t    .y = 3\r\n\t};\r\n    Doh set4[]=\r\n    {\r\n        {\r\n            .y  = 1039      \r\n        },\r\n        {\r\n            .y  = 1040,\r\n            .x  = 23\r\n        }\r\n    };<\/code><\/pre>\n
Still not rocket science, but the truly interesting part is that designated initializers are not<\/strong> yet available in C++.  At least not today.  I tested it with gcc 4.1.2 and Visual Studio 2008 C++ compilers and they do not support it.  It may appear in C++0x<\/a>, but for now, C is definitely no longer a pure subset of C++.  For more possible gotchas (and some C99 features that make it more<\/strong> compatible with C++), here’s a quick C99 rundown<\/a>.<\/p>\n
Considering designated initializers are being used in places like the linux kernel, this issue no longer seems trivial.  Oh well, code and learn.  Hopefully I can go another 10 years(!) before my next snag.  For now, back to classes<\/strong>…  :><\/p>\n","protected":false},"excerpt":{"rendered":"
Recently, I found myself kind of annoyed by the fact that I couldn’t use the same “initialization” syntax to directly set the values of an existing structure. Extremely trivial, but it bugs me. Is there really a good reason for this limitation? typedef struct { int x; int y; } Doh; Doh doh = { […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_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},"jetpack_post_was_ever_published":false},"categories":[22],"tags":[37],"class_list":["post-769","post","type-post","status-publish","format-standard","hentry","category-cpp","tag-c0x"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t