Hi Orivej, Luís thanks for your help - the code works finally now. See the method defined in the end of the file:
https://bitbucket.org/vityok/cl-gdal/src/75b9b957b29767a55349282eb4d3389fafae5387/src/ogr-spatialref.lisp?at=default The CPL-FREE function for whatever reason is not exported by the library (contrary to what I expect based on the documentation). But I'm fine with it at the moment. BTW, any feedback or advice on CL-GDAL library is welcome. Thanks! Victor 15.07.2015 04:26, Orivej Desh <c...@orivej.org> >> I don't know if it is the best place to ask this question, but I'll try it. >> I am trying to wrap around a following function: > > > > OGRErr OSRExportToProj4(OGRSpatialReferenceH r, char **buff); > > > > This function allocates the string and assigns it to the (char*) pointer > > passed as buff and then its contents should be copied into a C string and > > the obtained pointer released via CPLFree(); > > For the sake of example, I assume the pointer size is 8 bytes. > > First you learn elsewhere that OGRSpatialReferenceH is a pointer and OGRErr > is an int. [1] > > Then you know that OSRExportToProj4 takes two pointers and writes to the > memory addressed by the second argument a pointer (char*), > so the second argument must point to an allocated memory region 8 bytes in > size; in CFFI, you usually allocate memory using WITH-FOREIGN-OBJECT. > > After OSRExportToProj4 wrote a pointer to a C-string into that region of > memory, you can read it back in CFFI as a pointer using (MEM-REF ... > :POINTER). > > When you hold a pointer to a C-string, you can convert it into a Lisp string > with FOREIGN-STRING-TO-LISP. > > Overall, you need something like > > (cffi:defcfun (%osr-export-to-proj-4 "OSRExportToProj4") :int > (handle :pointer) > (*str :pointer)) > > (defun osr-export-to-proj-4 (handle) > (cffi:with-foreign-object (*str :pointer) > (%osr-export-to-proj-4 handle *str) > (let ((str (cffi:mem-ref *str :pointer))) > (unwind-protect (cffi:foreign-string-to-lisp str) > (cpl-free str))))) > > > [1] One way to learn it is with c2ffi (https://github.com/rpav/c2ffi): > > $ c2ffi -D sexp /usr/include/gdal/ogr_geometry.h 2>/dev/null | awk '$2 ~ > "OGRErr|OGRSpatialReferenceH|OSRExportToProj4" {print}' > (typedef OGRErr :int) > (typedef OGRSpatialReferenceH (:pointer :void)) > (function "OSRExportToProj4" ((OGRSpatialReferenceH) ((:pointer (:pointer > :char)))) OGRErr) -- реклама ----------------------------------------------------------- FREEhost.UA - быстрый и удобный хостинг доступный каждому. http://freehost.com.ua/unix/
