c++ - Storing lvalue reference to a dynamically allocated array -


consider following class of custom array

template <typename element, unsigned int size> class array { private: element (&data)[size]; public: array(element (&reference)[size]):data(reference){} array():data(new element [size]){} // problem arises };

obviously, in initialization list of constructor evaluates rvalue expression (the new-expression) rvalue of pointer instead of reference type. in msvc (microsoft visual studio 2012 rc) prompts error type conversion element * element (&)[size].

however, think if can perhaps convert rvalue pointer reference, should compile. there chance can make there in initialization list of constructor? or perhaps conflicts principle of c++ language? i've investiaged reinterpret_cast, rule find relevant is

"an lvalue expression of type t1 can converted reference type t2. result lvalue or xvalue referring same object original lvalue, different type." - cppreference.com

which states conversion applies lvalue expression.

ok, know might think - why need such class of custom array , why don't composite pointer instead of problemtic reference? well...you need different approaches choose before knowning best don't you?

what's c++11 , rvalue references? lvalue expression value pointed pointer, use unary * operator. it's been part of language since beginning. have here make sure pointer array, rather pointer first element of array.

template <typename element, unsigned int size> class array { private: element (&data)[size]; public: array() : data(*new element[1][size]) { } array(element (&reference)[size]) : data(reference) { } };

as mentioned mat in comment, parameterless constructor here bad idea, because memory not freed. hopefully, having working code sample allow experiment bit , come same conclusion.


Comments

Post a Comment

Popular posts from this blog

javascript - backbone.js Collection.add() doesn't `construct` (`initialize`) an object -

<!doctype html public "-//w3c//dtd xhtml 1.0 strict//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-strict.dtd"> <html> <head> <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script> <script src="http://documentcloud.github.com/underscore/underscore-min.js"></script> <script src="http://documentcloud.github.com/backbone/backbone-min.js"></script> </head> <body> <button id="cmd_create_event" name="cmd_create_event" type="button">create new `event`</button> <script type="text/javascript"> var eventmodel = backbone.model.extend({ initialize : function() { console.log("`event` initialized. id: " + this.cid); this.bind("change:status", function() { console.log(this.get("status") + " value `status`"); }); this.bind("error", function(model, e...
Read more

php - Get uncommon values from two or more arrays -

is there function in php give array of uncommon values 2 or more arrays? for example: $array1 = array( "green", "red", "blue"); $array2 = array( "green", "yellow", "red"); .... $result = function_needed($array1, $array2,...); print_r($result); should give output: array("blue", "yellow", ...); use array_diff , array_merge : $result = array_merge(array_diff($array1, $array2), array_diff($array2, $array1)); here's demo. for multiple arrays, combine callback , array_reduce : function unique(&$a, $b) { return $a ? array_merge(array_diff($a, $b), array_diff($b, $a)) : $b; } $arrays = array( array('green', 'red', 'blue'), array('green', 'yellow', 'red') ); $result = array_reduce($arrays, 'unique'); and here's demo of that.
Read more

Adding duplicate array rows in Php -

i create function in php adds rows of array shared column value. so input. $test = array( array("c", 5, 6), array("c", 2, 3), array("test", 5, 6) ); and output. $testduplicatefree = array( array("c", 7, 9), array("test", 5, 6) ) ); i'm thinking function combine_duplicates($array,$col){ ... ... return $duplicatefreearray; } where $col duplicate free array. so, in case, combine_duplicates($test,0); would me desired output. this. <?php function combine_duplicates($array,$col) { $index = array(); foreach ($array $row) { $key = $row[$col]; if (!isset($index[$key])) { $index[$key] = $row; } else { ($i = 0; $i < count($row); ++$i) { if ($i != $col) { $index[$key][$i] += $row[$i]; } } } } return array_values($index); } $array = array( array("c", 5, 6), array("c", 2, 3), array("test", 5, 6) ); print_r(combine_duplicates($array, 0)); try here: http://codepad.org/mdhesqhi
Read more