{"id":213,"date":"2020-08-31T11:28:23","date_gmt":"2020-08-31T11:28:23","guid":{"rendered":"https:\/\/www.kindsonthegenius.com\/cplusplus\/?p=213"},"modified":"2020-08-31T11:29:28","modified_gmt":"2020-08-31T11:29:28","slug":"c-references","status":"publish","type":"post","link":"https:\/\/www.kindsonthegenius.com\/cplusplus\/c-references\/","title":{"rendered":"C++ References"},"content":{"rendered":"

The concepts of references\u00a0 is one of the key concepts in programming. This is regardless of the programming language. So ensure you understand it since is quite easy and clear. Also since it relates to pointer, it’s better you go over C++ Pointers<\/a> first before you continue.<\/p>\n

    \n
  1. What are References<\/a><\/li>\n
  2. Creating References in C++<\/a><\/li>\n
  3. Passing Parameters by Reference<\/a><\/li>\n
  4. References as Function Return Value<\/a><\/li>\n<\/ol>\n

     <\/p>\n

    1. What are References?<\/strong><\/h4>\n

    A reference variable or just reference, is a variable that refers to an existing variable. Once you create a reference, then you can refer to to variable using that reference.<\/p>\n

    Is this not the same as pointers? Well, no. Here are the differences<\/p>\n

    References vs Pointers<\/strong><\/p>\n\n\n\n\n\n\n
    References<\/td>\nPointers<\/td>\n<\/tr>\n
    You cannot have NULL references<\/td>\nYou can have NULL pointers<\/td>\n<\/tr>\n
    Once initialized, a reference cannot be changed to reference another object<\/td>\nPointers can be modified to point to another object at any time<\/td>\n<\/tr>\n
    A reference must be initialized at creation time<\/td>\nPointers can be initialized at any time<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

     <\/p>\n

    2. Creating References in C++<\/strong><\/h4>\n

    A reference can be thought of an an alias of a variable name. So in the code below, we have a variable x. So we create a reference variable r to refer to x.<\/p>\n

    \/\/ declare a variables, x<\/span>\r\nint<\/span> x =<\/span> 34<\/span>;\r\n\r\n\/\/ create a reference rx<\/span>\r\nint<\/span>&<\/span> rx =<\/span> x \r\n<\/pre>\n
    The program below shows the use of references.<\/p>\n
    int<\/span> main<\/span> () {\r\n\t   \/\/ declare two normal variables<\/span>\r\n\t   int<\/span>    a;\r\n\t   double<\/span> b;\r\n\t \r\n\t   \/\/ declare two reference variables<\/span>\r\n\t   int<\/span>&<\/span>    ra =<\/span> a;\r\n\t   double<\/span>&<\/span> rb =<\/span> b;\r\n\t   \r\n\t   a =<\/span> 100<\/span>;\r\n\t   cout <<<\/span> \"Value of a : \"<\/span> <<<\/span> a <<<\/span> endl;\r\n\t   cout <<<\/span> \"Value of ra reference : \"<\/span> <<<\/span> ra  <<<\/span> endl;\r\n\t \r\n\t   b =<\/span> 70.25<\/span>;\r\n\t   cout <<<\/span> \"b has a value of : \"<\/span> <<<\/span> b <<<\/span> endl;\r\n\t   cout <<<\/span> \"The reference has a value of : \"<\/span> <<<\/span> rb  <<<\/span> endl;\r\n\t   \r\n\t   return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
    The output of this program is:
    \n<\/p>\n
    Value of a : 100\r\nValue of ra reference : 100\r\nb has a value of : 70.25\r\nThe reference has a value of : 70.25\r\n<\/pre>\n
    So you can see that references, a like another name for the variable is references.<\/p>\n
     <\/p>\n
    3. Passing Parameter by Reference<\/strong><\/h4>\n
    You may wonder. Why do we need references? Well in many cases, passing parameter by reference would lead to optimized memory utilization. Passing parameter by reference, means that the formal parameters are reference variables. So they are references to the actual parameters. Example is given the the following code.<\/p>\n
    int<\/span> main<\/span> () {\r\n\t   \/\/ declare two normal variables<\/span>\r\n\t   int<\/span> x =<\/span> 10<\/span>;\r\n\t   int<\/span> y =<\/span> 20<\/span>;\r\n\t   \r\n\t   cout <<<\/span> \"Value of x and y before swap\"<\/span> <<<\/span> endl;\r\n\t   cout <<<\/span> \"x before swap : \"<\/span> <<<\/span> x <<<\/span> endl;\r\n\t   cout <<<\/span> \"y before swap : \"<\/span> <<<\/span> y  <<<\/span> endl;\r\n\t   \r\n\t   \/\/ call swap() to swap the two numbers<\/span>\r\n\t   swap(x, y);\r\n\r\n\t   cout <<<\/span> \"Value of x and y after swap\"<\/span> <<<\/span> endl;\r\n\t   cout <<<\/span> \"x after swap : \"<\/span> <<<\/span> x <<<\/span> endl;\r\n\t   cout <<<\/span> \"y after swap : \"<\/span> <<<\/span> y  <<<\/span> endl;\r\n\r\n\t   return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
    The program would give the following output<\/p>\n
    Value of x and y before swap\r\nx before swap : 10\r\ny before swap : 20\r\nValue of x and y after swap\r\nx after swap : 20\r\ny after swap : 10\r\n<\/pre>\n
     <\/p>\n
    4. Reference as Function Return Value<\/strong><\/h4>\n
    A function have be made to return a reference. When a function returns a reference, then it kind of returns a pointer to its return value<\/p>\n
    #include <iostream><\/span>\r\n\r\nusing<\/span> namespace<\/span> std;\r\n\r\ndouble<\/span> scores[] =<\/span> { 67.5<\/span>, 98.8<\/span>, 75.7<\/span>};\r\n\r\ndouble<\/span>&<\/span> setValues( int<\/span> i ) {\r\n   return<\/span> scores[i];   \/\/ return a reference to the ith element<\/span>\r\n}\r\n\r\n\/\/ main function<\/span>\r\nint<\/span> main () {\r\n\r\n   cout <<<\/span> \"Scores before change\"<\/span> <<<\/span> endl;\r\n   for<\/span> ( int<\/span> i =<\/span> 0<\/span>; i <<\/span> 3<\/span>; i++<\/span> ) {\r\n      cout <<<\/span> \"scores[\"<\/span> <<<\/span> i <<<\/span> \"] = \"<\/span>;\r\n      cout <<<\/span> scores[i] <<<\/span> endl;\r\n   }\r\n\r\n   setValues(0<\/span>) =<\/span> 100.0<\/span>; \/\/ change 1st element<\/span>\r\n   setValues(2<\/span>) =<\/span> 100.0<\/span>;  \/\/ change 3rd element<\/span>\r\n\r\n   cout <<<\/span> \"Scores after change\"<\/span> <<<\/span> endl;\r\n   for<\/span> ( int<\/span> i =<\/span> 0<\/span>; i <<\/span> 3<\/span>; i++<\/span> ) {\r\n      cout <<<\/span> \"scores[\"<\/span> <<<\/span> i <<<\/span> \"] = \"<\/span>;\r\n      cout <<<\/span> scores[i] <<<\/span> endl;\r\n   }\r\n   return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
    The program above would produce the following output.<\/p>\n
    Scores before change\r\nscores[0] = 67.5\r\nscores[1] = 98.8\r\nscores[2] = 75.7\r\nScores after change\r\nscores[0] = 100\r\nscores[1] = 98.8\r\nscores[2] = 100\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
    The concepts of references\u00a0 is one of the key concepts in programming. This is regardless of the programming language. So ensure you understand it since … <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-213","post","type-post","status-publish","format-standard","hentry","category-c-tutorials"],"_links":{"self":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts\/213","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/comments?post=213"}],"version-history":[{"count":3,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts\/213\/revisions"}],"predecessor-version":[{"id":216,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/posts\/213\/revisions\/216"}],"wp:attachment":[{"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/media?parent=213"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/categories?post=213"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/cplusplus\/wp-json\/wp\/v2\/tags?post=213"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}