Converting a void to return something

Question

I have this void function in c++

void DrawFace(cv::Mat img, Window face)
{
    int x1 = face.x;
    int y1 = face.y;
    int x2 = face.width + face.x - 1;
    int y2 = face.width + face.y - 1;
    int centerX = (x1 + x2) / 2;
    int centerY = (y1 + y2) / 2;
    std::vector<cv::Point> pointList;
    pointList.push_back(RotatePoint(x1, y1, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x1, y2, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x2, y2, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x2, y1, centerX, centerY, face.angle));
    DrawLine(img, pointList);
}

i wanted this to return me just the pointList vector for which i made this change

void Drawface(cv::Mat img, Window face) 
{
    int x1 = face.x;
    int y1 = face.y;
    int x2 = face.width + face.x - 1;
    int y2 = face.width + face.y - 1;
    int centerX = (x1 + x2) / 2;
    int centerY = (y1 + y2) / 2;
    std::vector<cv::Point> pointList;
    pointList.push_back(RotatePoint(x1, y1, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x1, y2, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x2, y2, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x2, y1, centerX, centerY, face.angle));
    return pointList
}

It would be really helpful if somebody could point out where i have gone wrong and what changes i could make.

Thanks in advance

Change the signature of the function to `std::vector Drawface(cv::Mat img, Window face)`. — Ted Lyngmo, Dec 20 '18 at 12:32
https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list — Biffen, Dec 20 '18 at 12:32
@Ryan Great! Note that this is exactly the same as Vittorio suggests in his answer if you read it closely ("_....return type is still `void`. You need to change it to reflect the changes in the body_"). — Ted Lyngmo, Dec 20 '18 at 12:50
Easy alternative - change declaration "void Drawface(cv::Mat img, Window face)" and add a reference pointList to the parameter list: "void Drawface(cv::Mat img, Window face, std::vector& pointList)" — 2785528, Dec 21 '18 at 18:34

score 5 · Accepted Answer · answered Dec 20 '18 at 12:29

5

Your function's return type is still void. You need to change it to reflect the changes in the body. Also, missing a semicolon after return pointList.

answered Dec 20 '18 at 12:29

Vittorio Romeo

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Hi ,Thanks , i have added the semicolon, i have also removed the void.Now it looks like `Drawface(cv::Mat img, Window face)` ,is this okay? – Ryan Dec 20 '18 at 12:31
3

No. You obviously need to read a beginner C++ book. StackOverflow is not the right place to help you with the basics such as function signatures. See: https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list – Vittorio Romeo Dec 20 '18 at 12:32
Okay ,cool .Thanks for the help though ,ill look into it. – Ryan Dec 20 '18 at 12:32

score 4 · Answer 2 · answered Dec 20 '18 at 12:58

You need to declare the return type of the function.

std::vector<cv::Point> Drawface(cv::Mat img, Window face) 
{
    int x1 = face.x;
    int y1 = face.y;
    int x2 = face.width + face.x - 1;
    int y2 = face.width + face.y - 1;
    int centerX = (x1 + x2) / 2;
    int centerY = (y1 + y2) / 2;
    std::vector<cv::Point> pointList;
    pointList.push_back(RotatePoint(x1, y1, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x1, y2, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x2, y2, centerX, centerY, face.angle));
    pointList.push_back(RotatePoint(x2, y1, centerX, centerY, face.angle));
    return pointList;
}

Converting a void to return something

2 Answers2