Merge pull request #5502 from AlexanderStohr:file-handle-volatile-fix

modules/imgcodecs/src/grfmt_png.cpp

@@ -368,7 +368,7 @@ bool  PngEncoder::write( const Mat& img, const std::vector<int>& params )
                 {
                     f = fopen( m_filename.c_str(), "wb" );
                     if( f )
-                        png_init_io( png_ptr, f );
+                        png_init_io( png_ptr, (png_FILE_p)f );
                 }
 
                 int compression_level = -1; // Invalid value to allow setting 0-9 as valid
@@ -437,7 +437,7 @@ bool  PngEncoder::write( const Mat& img, const std::vector<int>& params )
     }
 
     png_destroy_write_struct( &png_ptr, &info_ptr );
-    if(f) fclose( f );
+    if(f) fclose( (FILE*)f );
 
     return result;
 }

modules/videoio/src/cap_ffmpeg_impl.hpp

@@ -586,6 +586,7 @@ bool CvCapture_FFMPEG::open( const char* _filename )
     if (err < 0)
     {
         CV_WARN("Error opening file");
+        CV_WARN(_filename);
         goto exit_func;
     }
     err =

modules/videoio/src/cap_gstreamer.cpp

@@ -601,6 +601,8 @@ bool CvCapture_GStreamer::open( int type, const char* filename )
             else
             {
                 CV_WARN("GStreamer: Error opening file\n");
+                CV_WARN(filename);
+                CV_WARN(uri);
                 close();
                 return false;
             }