‘Mat’ was not declared in this scope opencv

Question

I followed this guide to install openCV on Ubuntu: https://docs.opencv.org/master/d7/d9f/tutorial_linux_install.html

When I try to execute the following program:

#include <opencv2/core/core.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream> 
#include <math.h>
#include <tiffio.h>

using namespace std;

int main(){
  string imageName("images/400nm.tif");
  TIFF* tif = TIFFOpen(imageName.c_str(), "r");
  Mat image;


  return 0;
}

I get the following error executing the command "g++ ssim.cpp -o ssim -ltiff":

ssim.cpp: In function ‘int main()’: ssim.cpp:19:3: error: ‘Mat’ was not declared in this scope Mat image; ^~~ ssim.cpp:19:3: note: suggested alternative: In file included from /usr/local/include/opencv2/core.hpp:59:0, from /usr/local/include/opencv2/core/core.hpp:48, from ssim.cpp:2: /usr/local/include/opencv2/core/mat.hpp:771:18: note: ‘cv::Mat’ class CV_EXPORTS Mat

Does somebody know why I get this and how to solve it? I'm new at using opencv and libtiff so I have no idea about what to do to solve...

I don't understand what should I do... I tried to add "using namespace cv" or to use "cv::Mat" but nothing happen. — Davide57
Try to compile #include <opencv2/core/core.hpp> int main(){ cv::Mat image; return 0; } Do you get the same error? — aparpara

Mathis Witte Mathis Witte · Accepted Answer · 2018-08-15T13:02:08

It's not really necessary to build openCV from source. Try installing it with

sudo apt-get install libopencv-dev

and try to compile it again.

Also like you said in your comment, make sure you either use namespace cv or cv::Mat.

‘Mat’ was not declared in this scope opencv

2 Answers