Trying to set a window's opacity, but the compiler gives this: [Linker error] undefined reference to `SetLayeredWindowAttributes'. I included User32.lib (libuser32.a using Dev-C++) like msdn said to, but I still got the error. Next I tried downloading the lib from the site I got pdh.def off. Still no luck. Looking in the def file: no wonder - It made no reference to the function. Where is this function referenced? Is it even in user32 or is msdn wrong? Edit: Is this a new function that was only introduced in the latest version of user32.dll? Also, has anyone ever got a semi-transparent window working in Dev-C++?