Add string->pointer' and pointer->string' to the FFI.

* libguile/foreign.c (scm_string_to_pointer, scm_pointer_to_string): New
  functions.

* libguile/foreign.h (scm_string_to_pointer, scm_pointer_to_string): New
  declarations.

* module/system/foreign.scm: Export `string->pointer' and
  `pointer->string'.

* test-suite/tests/foreign.test ("pointer<->string"): New test prefix.

* doc/ref/api-foreign.texi (Void Pointers and Byte Access): Add
  `string->pointer' and `pointer->string'.

doc/ref/api-foreign.texi

@@ -598,6 +598,22 @@ Assuming @var{pointer} points to a memory region that holds a pointer,
 return this pointer.
 @end deffn
 
+@deffn {Scheme Procedure} string->pointer string
+Return a foreign pointer to a nul-terminated copy of @var{string} in the
+current locale encoding.  The C string is freed when the returned
+foreign pointer becomes unreachable.
+
+This is the Scheme equivalent of @code{scm_to_locale_string}.
+@end deffn
+
+@deffn {Scheme Procedure} pointer->string pointer
+Return the string representing the C nul-terminated string
+pointed to by @var{pointer}.  The C string is assumed to be
+in the current locale encoding.
+
+This is the Scheme equivalent of @code{scm_from_locale_string}.
+@end deffn
+
 Going back to the @code{scm_numptob} example above, here is how we can
 read its value as a C @code{long} integer:
 

libguile/foreign.c

@@ -162,18 +162,6 @@ SCM_DEFINE (scm_pointer_address, "pointer-address", 1, 0, 0,
 }
 #undef FUNC_NAME
 
-SCM_DEFINE (scm_dereference_pointer, "dereference-pointer", 1, 0, 0,
-	    (SCM pointer),
-	    "Assuming @var{pointer} points to a memory region that\n"
-	    "holds a pointer, return this pointer.")
-#define FUNC_NAME s_scm_dereference_pointer
-{
-  SCM_VALIDATE_POINTER (1, pointer);
-
-  return scm_from_pointer (* (void **) SCM_POINTER_VALUE (pointer), NULL);
-}
-#undef FUNC_NAME
-
 SCM_DEFINE (scm_pointer_to_bytevector, "pointer->bytevector", 2, 2, 0,
 	    (SCM pointer, SCM len, SCM offset, SCM uvec_type),
 	    "Return a bytevector aliasing the @var{len} bytes pointed\n"
@@ -299,8 +287,6 @@ SCM_DEFINE (scm_set_pointer_finalizer_x, "set-pointer-finalizer!", 2, 0, 0,
 }
 #undef FUNC_NAME
 
-
-
 void
 scm_i_pointer_print (SCM pointer, SCM port, scm_print_state *pstate)
 {
@@ -309,6 +295,55 @@ scm_i_pointer_print (SCM pointer, SCM port, scm_print_state *pstate)
   scm_putc ('>', port);
 }
 
+
+/* Non-primitive helpers functions.  These procedures could be
+   implemented in terms of the primitives above but would be inefficient
+   (heap allocation overhead, Scheme/C round trips, etc.)  */
+
+SCM_DEFINE (scm_dereference_pointer, "dereference-pointer", 1, 0, 0,
+	    (SCM pointer),
+	    "Assuming @var{pointer} points to a memory region that\n"
+	    "holds a pointer, return this pointer.")
+#define FUNC_NAME s_scm_dereference_pointer
+{
+  SCM_VALIDATE_POINTER (1, pointer);
+
+  return scm_from_pointer (* (void **) SCM_POINTER_VALUE (pointer), NULL);
+}
+#undef FUNC_NAME
+
+SCM_DEFINE (scm_string_to_pointer, "string->pointer", 1, 0, 0,
+	    (SCM string),
+	    "Return a foreign pointer to a nul-terminated copy of\n"
+	    "@var{string} in the current locale encoding.  The C\n"
+	    "string is freed when the returned foreign pointer\n"
+	    "becomes unreachable.\n\n"
+            "This is the Scheme equivalent of @code{scm_to_locale_string}.")
+#define FUNC_NAME s_scm_string_to_pointer
+{
+  SCM_VALIDATE_STRING (1, string);
+
+  /* XXX: Finalizers slow down libgc; they could be avoided if
+     `scm_to_string' & co. were able to use libgc-allocated memory.  */
+
+  return scm_from_pointer (scm_to_locale_string (string), free);
+}
+#undef FUNC_NAME
+
+SCM_DEFINE (scm_pointer_to_string, "pointer->string", 1, 0, 0,
+	    (SCM pointer),
+	    "Return the string representing the C nul-terminated string\n"
+	    "pointed to by @var{pointer}.  The C string is assumed to be\n"
+	    "in the current locale encoding.\n\n"
+	    "This is the Scheme equivalent of @code{scm_from_locale_string}.")
+#define FUNC_NAME s_scm_pointer_to_string
+{
+  SCM_VALIDATE_POINTER (1, pointer);
+
+  return scm_from_locale_string (SCM_POINTER_VALUE (pointer));
+}
+#undef FUNC_NAME
+
 
 
 SCM_DEFINE (scm_alignof, "alignof", 1, 0, 0, (SCM type),

libguile/foreign.h

@@ -69,10 +69,13 @@ SCM_API SCM scm_set_pointer_finalizer_x (SCM pointer, SCM finalizer);
 SCM_API SCM scm_bytevector_to_pointer (SCM bv, SCM offset);
 
 SCM_INTERNAL SCM scm_make_pointer (SCM address, SCM finalizer);
-SCM_INTERNAL SCM scm_dereference_pointer (SCM pointer);
 SCM_INTERNAL void scm_i_pointer_print (SCM pointer, SCM port,
                                        scm_print_state *pstate);
 
+SCM_INTERNAL SCM scm_dereference_pointer (SCM pointer);
+SCM_INTERNAL SCM scm_string_to_pointer (SCM string);
+SCM_INTERNAL SCM scm_pointer_to_string (SCM pointer);
+
 
 
 /* Foreign functions */

module/system/foreign.scm

@@ -33,12 +33,15 @@
             null-pointer?
             make-pointer
             pointer-address
-            dereference-pointer
 
             pointer->bytevector
             bytevector->pointer
             set-pointer-finalizer!
 
+            dereference-pointer
+            string->pointer
+            pointer->string
+
             make-foreign-function
             make-c-struct parse-c-struct))
 

test-suite/tests/foreign.test

@@ -78,6 +78,18 @@
                      0
                      bytes)))))
 
+
+(with-test-prefix "pointer<->string"
+
+  (pass-if "bijection"
+    (let ((s "hello, world"))
+      (string=? s (pointer->string (string->pointer s)))))
+
+  (pass-if "bijection [latin1]"
+    (with-latin1-locale
+      (let ((s "Szép jó napot!"))
+        (string=? s (pointer->string (string->pointer s)))))))
+
 
 (with-test-prefix "structs"