c++ - User-declared namespace member -

-

there 3.4.1/14:

if variable member of namespace defined outside of scope of namespace name appears in definition of member (after declarator-id) looked if definition of member occurred in namespace.

if name treated definition of member name point of declaration?

and why following example works:

namespace n  {     extern int j; } int = 2; int n::j = i; //n::j=2

int n::j=i actual appears namespace scope. hence declarationint i=2 not visible unqualified name lookup. why declaration found?

your question:

int n::j=i actual appears namespace scope. hence declaration int i=2 not visible unqualified name lookup. why declaration found?

answer:

since i not found in n namespace, looked in global namespace. had i been there in n namespace, have been used initialize n::j.

hope following program clarifies doubt.

#include <iostream>  namespace n  {    extern int j;    extern int k;     int x = 3; }  int x = 2; int y = 10;  int n::j = x; // n::x used initialize n::j int n::k = y; // ::y used initialize n::k  int main() {    std::cout << n::j << std::endl;    std::cout << n::k << std::endl; }

output:

 3 10

update, in response comment op

what standard saying that:

namespace n  {    extern int j; }  int x = 2;  int n::j = x;

is equivalent to:

namespace n  {    extern int j; }  int x = 2;  namespace n  {    int j = x; }

the logic lookup ofx same. if found within same namespace n, used. if x not found in namespace n, searched outward in enclosing namespaces.


Comments

Post a Comment

Popular posts from this blog

php - render data via PDO::FETCH_FUNC vs loop -

-
i've been using 2 methods render data. the first one: function name($id,$name){ return '<div id="'.$id.'">'.$name.'</div>'; } echo implode($pdo->query("select id,name user")->fetchall(pdo::fetch_func,'name')); the second one: $users = $pdo->query("select id,name user")->fetchall(pdo::fetch_obj); foreach($users $user){ echo name($user->id,$user->name); } i don't understand how pdo::fetch_func works. tried figure out. however, not well-documented. could please explain fetch mode? , also, 1 performs better? thank you. both methods wrong , have learn how use templates , how separate business logic presentation logic. $users = $pdo->query("select id,name user")->fetchall(pdo::fetch_obj); tpl::assign('users', $users); is code business logic part. then in template <?php foreach $users $row): ?> <div id="<?=$...
Read more

c++ - OpenCV Error: Assertion failed <scn == 3 ::scn == 4> in unknown function, -

-
i read alot other solution still confused should mine... #include <opencv2/objdetect/objdetect.hpp> #include <opencv2/highgui/highgui.hpp> #include <opencv2/imgproc/imgproc.hpp> #include <iostream> #include <stdio.h> using namespace std; using namespace cv; int main(int argc, const char** argv) { //create cascade classifier object used face detection cascadeclassifier face_cascade; //use haarcascade_frontalface_alt.xml library face_cascade.load("haarcascade_frontalface_alt.xml"); //setup video capture device , link first capture device videocapture capturedevice; capturedevice.open(0); //setup image files used in capture process mat captureframe; mat grayscaleframe; //create window present results namedwindow("outputcapture", 1); //create loop capture , find faces while (true) { //capture new image frame capturedevice >> captureframe; ...
Read more

The canvas has been tainted by cross-origin data in chrome only -

-
uncaught securityerror: failed execute 'getimagedata' on 'canvasrenderingcontext2d': canvas has been tainted cross-origin data i getting above error in chrome. code(following) works fine in mozilla. have not corss domain issue. why above error in chrome? var wheel_canvas, wheel_context, can_w, can_h, wheel_grd; var large_radius = 160; var small_radius = 120; var wheel_canvas = document.getelementbyid('wheel_canvas'); var wheel_context = wheel_canvas.getcontext('2d'); var can_w = $(wheel_canvas).width(); var can_h = $(wheel_canvas).height(); var centerx = can_w / 2, centery = can_h / 2; var wheel_grd = null; test('#ff0000'); function test(hex) { $('#clrpicker').css({'left': 210, 'top': 210 }); inverted = hexbw(hex); $('#color_val_show').val(hex); current_color_hex_val_selected = hex; $('#color_val_show').css({'color':inverted,'background':hex}); fillgradient...
Read more