Question

was just wondering, how are GUI libraries like GTK, wxWidget written ?? i mean what language or tools are used ...

Answer 1

Such UI toolkits interface directly with the platform's APIs to do their drawing and event handling. For example, a UI toolkit like Qt or Gtk may use the oeprating system's functions to draw text and boxes, and the OS functionality to catch mouse clicks, and use them to implement functionality for a button. The toolkit's user can then simply use the button functionality instead of stitching those parts together themselves. For Windows XP for example, such a toolkit would have to use parts of the Win32 APIs like GDI, and access them in via C/C++ For MacOS, it would have to use Cocoa or Carbon. If a toolkit uses Cocoa, it would have to access the OS' functionality via Objective-C. For Linux, Qt, for example, uses XRender in combination with a few other libraries and APIs like freetype and the X11 client library.
As such, the language these toolkits are written in can vary. Most are written in C or C++ though. Qt is written mostly in C++, Gtk in C (and I believe so is wxWidgets).