{"id":225,"date":"2019-01-25T23:35:25","date_gmt":"2019-01-26T07:35:25","guid":{"rendered":"http:\/\/35.243.195.209\/?p=225"},"modified":"2019-01-25T23:39:48","modified_gmt":"2019-01-26T07:39:48","slug":"const-pointers-and-references","status":"publish","type":"post","link":"https:\/\/nanzhou.cc\/index.php\/2019\/01\/25\/const-pointers-and-references\/","title":{"rendered":"Const, Pointers and References"},"content":{"rendered":"

Summary<\/h2>\n

In this post, I will introduce const<\/code>, *<\/code> and &<\/code> and their combinations. I also have similar posts discussed auto<\/code> and &<\/code><\/a>.<\/p>\n

Conclusion<\/h2>\n

As usual, I present the golden rule first: “read from right to left”<\/strong>. In other words, the const-on-the-right style<\/strong> always puts the const on the right of what it constifies”.<\/p>\n

    \n
  1. When you want a pointer which can not change the object, use CNN const * cnn_ptr = new CNN(model);<\/code>;<\/li>\n
  2. When you want a pointer which can not point to other objects, use CNN * const cnn_ptr = new CNN(model);<\/code>;<\/li>\n
  3. When you want a pointer which can not change the object and can not point to other objects, use CNN const * const cnn_ptr = new CNN(model);<\/code><\/li>\n
  4. When you want a reference which can not change the object, use CNN const & cnn_ref = model;<\/code>;<\/li>\n<\/ol>\n

    Details<\/h2>\n

    1. const CNN *<\/code> or CNN const *<\/code><\/h3>\n

    Read it from right to left. CNN const * cnn_ptr<\/code> means \u201ccnn_ptr points to an CNN instance that is const\u201d: the CNN object can\u2019t be changed via cnn_ptr<\/code>. CNN const * cnn_ptr<\/code> is equivalent to CNN const * cnn_ptr<\/code>. However, I prefer the former, which is the const-on-the-right<\/strong> style.<\/p>\n

    The const-on-the-right is a consistent style: it always puts the const on the right of what it constifies. In which, a local variable that is const is defined with the const on the right: int const a = 42;<\/code>. Similarly a static variable that is const is defined as static double const x = 3.14;<\/code>. Basically every const ends up on the right of the thing it constifies.<\/p>\n

    2. CNN * const cnn_ptr<\/code><\/h3>\n

    Read it from right to left. CNN * const cnn_ptr<\/code> means \u201ccnn_ptr is a const pointer to an CNN instance that is non-const\u201d: you can\u2019t change the pointer cnn_ptr itself, but you can change the CNN object via the cnn_ptr. const<\/code> constifies *<\/code>, which makes us happy.<\/p>\n

    3. CNN const * const cnn_ptr<\/code><\/h3>\n

    Read it from right to left. It means \u201ccnn_ptr is a const pointer to an CNN instance that is const\u201d: you can\u2019t change the pointer cnn_ptr itself, nor can you change the CNN instance via cnn_ptr.<\/p>\n

    4. CNN const & cnn_ref<\/code><\/h3>\n

    Read it from right to left. \u201ccnn_ref is a reference to a const CNN\u201d. CNN const & cnn_ref<\/code> is equivalent to const CNN & cnn_ref<\/code>.<\/p>\n

    5. CNN & const cnn_ref<\/code> ???<\/h3>\n

    \u201ccnn_ref is a const reference to a CNN\u201d? It makes no sense. Once combined, cnn_ref can not combine other instances. That is, CNN& const cnn_ref<\/code> is always equivalent to CNN& cnn_ref<\/code>.<\/p>\n

    Reference<\/h2>\n

    isocpp.org<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Summary In this post, I will introduce const, * and & and their combinations. I also have similar posts discussed auto and &. Conclusion As usual, I present the golden rule first: “read from right to left”. In other words, the const-on-the-right style always puts the const on the right of what it constifies”. When…<\/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-225","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\/225","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=225"}],"version-history":[{"count":4,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/225\/revisions"}],"predecessor-version":[{"id":232,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/225\/revisions\/232"}],"wp:attachment":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/media?parent=225"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/categories?post=225"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/tags?post=225"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}