C++ function takes ints, but example shows text? -

C++ function takes ints, but example shows text? -

this c++ question on confusing me. (i refreshing c++ after long time). reading illustration here. there 2 parts confuse me:

the first part:

in code line:

void namedwindow(const string& winname, int flags=window_autosize )

window_autosize input, far can tell, not int. when code line , run, works fine. input function literally 'window_autosize'. confused why works. how window_autosize int?

my sec question regarding lastly line, whereby say:

by default, flags == cv_window_autosize | cv_window_keepratio | cv_gui_expanded

i confused how/what means exactly... know | bitwise or, not clear means exactly...

thank you.

my input function literally 'window_autosize'

yep, window_autosize in fact integer; simply @ fact it's default argument int function parameter. wouldn't compile if wasn't int

// might have been defined #define window_autosize 23434 // number illustration // or const int window_autosize = 34234;

as sec question bitwise oring means bits in corresponding integral values ored together, lets example

cv_window_autosize = 0x0010 cv_window_keepratio = 0x0100 cv_gui_expanded = 0x1100

then corresponding operation give integral value every bit equal result of or each position

cv_window_autosize | cv_window_keepratio | cv_gui_expanded = 0x0010 0x0100 0x1100 ------ 0x1110 on utilize of bitflags

consider next : you have keyboard 4 keys :

ctrl, alt, del, shift

how many constants need define states keyboard can on ? lets enumerate states

all 4 keys pressed : 1 constant

3 keys pressed : takes (4 3) constants = 4 constants :

(4 3) = 4! / ( (4-3)! * 3! ) = 4

2 keys pressed : (4 2) = 6 constants

1 key pressed : 4 constants (the names of keys)

no key pressed : 1 constant

so sum you'd define :

1 + 4 + 6 + 4 + 1 = 16 constants

now if told need 4 different constants, each 1 having 1 bit on ? :

#define ctrlk 0x0001 #define altk 0x0010 #define delk 0x0100 #define shiftk 0x1000

then state keyboard can expressed combination of above : want express state shift key , del key pressed.

ctrlk | delk

the more combinations have, more technique pays off.

ofcourse (maybe see reference on bitflags) user code can probe integral value see bits switched on.

c++ function int bit-manipulation