compiler error in calling friend function!!??

[ChrisW67]

Assuming that friendFunction() will ultimately need access to private parts of your Window class (it doesn't at the moment as Santosh Reddy points out)...

Line 14 of window.h is a grant of privileges, not a forward declaration of a function friendFunction(), which is what is needed in order for your implementation to compile. Add this line:

void friendFunction();

void friendFunction();

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to the top of window.cpp. This forward declaration would typically be in a header included by the implementations that need to know that the function exists.