X-Git-Url: http://git.kpe.io/?a=blobdiff_plain;f=doc%2Fref.sgml;h=f299c197cee87f90e5045c6c1ddca6b4d89198c1;hb=340539a1be525ce05c7c06472c291fedaf09684a;hp=39ae02ebaf9a920fceb1b76cef1a1671bd0f70fb;hpb=005eb1c1210634a27fbc973d84004b5622456fc5;p=uffi.git
diff --git a/doc/ref.sgml b/doc/ref.sgml
index 39ae02e..f299c19 100644
--- a/doc/ref.sgml
+++ b/doc/ref.sgml
@@ -1498,21 +1498,51 @@ if a cstring returned by a function is &null;.
&uffi; has functions to two types of
C-compatible
- strings, cstring and foreign strings.
-
-cstrings are used as parameters to and from functions. An
-implementation, such as CMUCL and Lispworks, a cstring may not be a
-foreign type but rather the Lisp string itself while on other
-platforms a cstring is a newly allocated foreign vector for storing
-characters. Thus, it is not possible to portably
-allocate a cstring.
+ strings: cstring and
+foreign strings.
+
+cstrings are used only as parameters to and from
+functions. In some implementations a cstring is not a foreign type but
+rather the Lisp string itself. On other platforms a cstring is a newly
+allocated foreign vector for storing characters. The following is an
+example of using cstrings to both send and return a value.
-
-In contrast, foreign strings
-are always a foreign vector of characters which have a memory
-allocated to hold them. Because of this, if you need to allocate memory to
-hold the return value of a string, use a foreign string and not a cstring.
-
+
+
+(uffi:def-function ("getenv" c-getenv)
+ ((name :cstring))
+ :returning :cstring)
+
+(defun my-getenv (key)
+ "Returns an environment variable, or NIL if it does not exist"
+ (check-type key string)
+ (uffi:with-cstring (key-native key)
+ (uffi:convert-from-cstring (c-getenv key-native))))
+
+
+ In contrast, foreign strings are always a foreign vector of
+characters which have memory allocated. Thus, if you need to allocate
+memory to hold the return value of a string, you must use a foreign
+string and not a cstring. The following is an example of using a foreign
+string for a return value.
+
+
+(uffi:def-function ("gethostname" c-gethostname)
+ ((name (* :unsigned-char))
+ (len :int))
+ :returning :int)
+
+(defun gethostname ()
+ "Returns the hostname"
+ (let* ((name (uffi:allocate-foreign-string 256))
+ (result-code (c-gethostname name 256))
+ (hostname (when (zerop result-code)
+ (uffi:convert-from-foreign-string name))))
+ (uffi:free-foreign-object name)
+ (unless (zerop result-code)
+ (error "gethostname() failed."))))
+
+
@@ -1655,7 +1685,7 @@ that returns a cstring.
Description
Frees any memory possibly allocated by
- convert-to-cstring.
+ convert-to-cstring. On some implementions, a cstring is just the Lisp string itself.