title: How do you declare a function with definition func(cv::Mat &img) in C++
body: <p>How do you declare a function defined as such:</p>
  
  <pre><code>void func(cv::Mat &amp;img)
  {
      ...
  }
  </code></pre>
  
  <p><strong>More details:</strong></p>
  
  <p>I defined the function "func" in my main.cpp file below the "main" function. The compiler complained that it didn't know what the function "func" was, so I tried to put the prototype above the "main" function.</p>
  
  <p>I tried</p>
  
  <pre><code>void func(cv::Mat);
  </code></pre>
  
  <p>but that didn't work.</p>