When creating a C-STRING, leave only as many characters as dictated by the fill pointer

src/CHANGELOG

@@ -19,6 +19,9 @@ ECL 0.9g
  - DEF-FOREIGN-VAR rewritten to make variables visible from other files and to
    dereference also arrays and pointers. (M. Pasternacki)
 
+ - When creating a C-STRING, characters after the fill pointer are discarded,
+   according to people's expectations.
+
 * Compiler changes:
 
  - Generated C functions now have readable names corresponding to appropriate

src/lsp/ffi.lsp

@@ -372,13 +372,16 @@
   object)
 
 (defmacro convert-to-cstring (object)
-  object)
+  ;; This enforces that the string contains only as many characters as the
+  ;; fill-pointer determines Since ECL always sets a 0 character after the
+  ;; last element of a string, this way, the string is always zero-terminated
+  (copy-seq object))
 
 (defmacro free-cstring (object)
   object)
 
 (defmacro with-cstring ((cstring string) &body body)
-  `(let ((,cstring ,string)) ,@body))
+  `(let ((,cstring (copy-seq ,string))) ,@body))
 
 (defmacro with-cstrings (bindings &rest body)
   (if bindings