I'm trying to recreate a const char* filename parameter for code I have that needs it...The function I'm wrapping is the OpenCV C++ function "imread" it is below in the documentation. It is used to read an image(jpg etc) from a file and return a pointer to it http://docs.opencv.org/modules/highgui/doc/reading_and_writing_images_and_vi... first I need to wrap in C as below calling the const char* filename parameter as a String* the below cv_imread does compile on ubuntu trusty using g++. And the function works as intended using g++. Mat* cv_imread(String* filename, int flags) { return new Mat(cv::imread(*filename, flags)); } I wrap in Lisp like this: (defcfun ("cv_imread" %imread) (:pointer mat) (filename (:pointer string*)) (flags :int)) When I usually create a (:pointer string*) parameter I do it like this (window-name (foreign-alloc :string :initial-element "IMREAD Example")) and it works to supply strings that aren't filenames but when I try to use a filename both absolute and relative paths it fails...it also fails using double forward slashes in the pathname. Any advice is appreciated and btw Emacs /SBCL is my Lisp IDE