c++ - How are function definitions determined with header files? -

-

when using separate files in c++, know functions can declared using header files this:

// myheader.h  int add(int num, int num2); 
// mysource.cpp  int add(int num, int num2) {     return num + num2; } 
// main.cpp  #include "myheader.h" #include <iostream>  int main() {     std::cout << add(4, 5) << std::endl;     return 0; }

my question is, in situation, how compiler determine function definition of add(int,int) when myheader.h , main.cpp have no references @ mysource.cpp?

as, if there multiple add functions (with same arguments) in program, how can make sure correct 1 being used in situation?

the function declaration gives compiler enough information generate call function.

the compiler generates object file specifies names (which, in case of c++ mangled specify arguments, namespace, cv-qualifiers, etc.) of external functions object file refers (along list of names defines).

the linker takes object files, , tries match every name refers doesn't define other object file defines same name. assigns , fills in addresses, 1 object file refers namex, fills in address it's assigning namex other file.

at least in typical case, object files looks @ include number of libraries (standard library + others specify). library collection of object files, shoved single file, enough data index data object file. in few cases, includes meta-data (for example) find object file defines specific name (obviously handy sake of faster linking, not absolute necessity).

if there 2 or more functions same mangled name, code has undefined behavior (you're violating 1 definition rule). linker usually give error message telling namez defined in both object file , object file b (but c++ standard doesn't require that).


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