If I understand the question correctly then this is indeed about a basic part of c++.
With some basic type:
You are in the exact same situation as the last line, you need a RenderWindow while you only have a RenderWindow* (just like you needed an int and had an int*).
So you can just initialize the gui like this:
With some basic type:
Code (c++) Select
int i1 = 0; // Create an integer
int* p = &i1; // Create a pointer with the address of i1
int i2 = *p; // Dereference the pointer (get the value of i1)
You are in the exact same situation as the last line, you need a RenderWindow while you only have a RenderWindow* (just like you needed an int and had an int*).
So you can just initialize the gui like this:
Code (c++) Select
tgui::Gui gui(*renderWindowPointer);