How to solve the problem on C2056 undeclared identifier

asked 2019-01-12 04:01:58 -0600

LCY
3 ●1

updated 2019-01-12 04:16:16 -0600

berak
32993 ●7 ●81 ●312

I having problem with this

void colortrackbar() {

        namedWindow("Color", CV_WINDOW_AUTOSIZE);
    cvCreateTrackbar("Blue", "Color", 0, 1, bluecolor_callback);
    cvCreateTrackbar("Green", "Color", 0, 1);
    cvCreateTrackbar("Red", "Color", 0, 1);
}

void bluecolor_callback(int position) {

    if (position == 0) {
        int H_MIN = 0;
        int H_MAX = 255;
        int S_MIN = 0;
        int S_MAX = 255;
        int V_MIN = 0;
        int V_MAX = 255;
    }
    else {
        int H_MIN = 0;
        int H_MAX = 255;
        int S_MIN = 110;
        int S_MAX = 255;
        int V_MIN = 148;
        int V_MAX = 255;
    }

and having error

C2065  "bluecolor_callback" : undeclared identifier

and I don't know how to solve the problem. Please help me, thank you.

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answered 2019-01-12 04:25:40 -0600

berak
32993 ●7 ●81 ●312

you have to declare your callback function, before you use it in the code

(also, you need a different signature !). like this:

 // declaration:
 void bluecolor_callback(int position, void*);

 int main() {
          ...
          // you HAVE TO use c++, not the deprecated c-api calls !!!!!
          cv::createTrackbar("Blue", "Color", 0, 1, bluecolor_callback);
          ...
 }

 // definition:
 void bluecolor_callback(int position, void*) {
         ... some code
 }

please also have another look at the tutorial

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Comments

must create trackbar at main function?

LCY ( 2019-01-12 04:28:00 -0600 )edit

must create trackbar at main function?

not nessecarily, that was just an example. but again, the declaration has to go before you use it.

berak ( 2019-01-12 04:29:22 -0600 )edit

ok thank you

LCY ( 2019-01-12 04:32:00 -0600 )edit

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Asked: 2019-01-12 04:01:58 -0600

Seen: 508 times

Last updated: Jan 12 '19

How to solve the problem on C2056 undeclared identifier edit