The LNK2019 unresolved external symbol occurs when linker couldnt find a definition for a refernce to a function or variable. i found good explaination here

How can I solve the error LNK2019: unresolved external symbol - function? https://learn.microsoft.com/en-us/cpp/error-messages/tool-errors/linker-tools-error-lnk2019?view=msvc-170

as per comments from VZ. and Igor.

You might have declared the constructor for dataPanel in your class definition but did not provide an implementation for it. The compiler finds the declaration but cannot locate the corresponding definition, causing the linker to fail.

Add the implementation of dataPanel::dataPanel in your .cpp file and make sure your dataPanel class is included in your main application file.

In your constructor file

#include <wx/wx.h>
#include "dataPanel.h" // Include the header file for dataPanel

dataPanel::dataPanel(wxFrame* parent)
    : wxPanel(parent, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxTAB_TRAVERSAL, "dataPanel")
{
    // Initialization code here (optional)
    SetBackgroundColour(*wxWHITE); // Example: Set background color to white
}