1.0.10.27: Change unportable find option "-path"

[sbcl.git] / doc / manual / ffi.texinfo

diff --git a/doc/manual/ffi.texinfo b/doc/manual/ffi.texinfo
index c8bc8d5..cfdd1d2 100644 (file)
--- a/doc/manual/ffi.texinfo
+++ b/doc/manual/ffi.texinfo
@@ -3,7 +3,7 @@
 @chapter Foreign Function Interface
 
 This chapter describes SBCL's interface to C programs and
-libraries (and, since C interfaces are a sort of @emph{ingua
+libraries (and, since C interfaces are a sort of @emph{lingua
 franca} of the Unix world, to other programs and libraries in
 general.)
 
@@ -196,8 +196,10 @@ variables. Dynamic arrays can only be allocated using
 The foreign type specifier @code{(sb-alien:struct @var{name} &rest
 @var{fields})} describes a structure type with the specified
 @var{name} and @var{fields}. Fields are allocated at the same offsets
-used by the implementation's C compiler. If @var{name} is @code{nil}
-then the structure is anonymous.
+used by the implementation's C compiler, as guessed by the SBCL
+internals. An optional @code{:alignment} keyword argument can be
+specified for each field to explicitly control the alignment of a
+field. If @var{name} is @code{nil} then the structure is anonymous.
 
 If a named foreign @code{struct} specifier is passed to
 @code{define-alien-type} or @code{with-alien}, then this defines,
@@ -281,13 +283,37 @@ types to declare that no useful value is returned.  Using
 return zero values.
 
 @item
-The foreign type specifier @code{sb-alien:c-string} is similar to
-@code{(* char)}, but is interpreted as a null-terminated string, and
-is automatically converted into a Lisp string when accessed; or if the
-pointer is C @code{NULL} or @code{0}, then accessing it gives Lisp
-@code{nil}.  Lisp strings are stored with a trailing NUL
-termination, so no copying (either by the user or the implementation)
-is necessary when passing them to foreign code.
+The foreign type specifier @code{(sb-alien:c-string &key external-format
+element-type)} is similar to @code{(* char)}, but is interpreted as a
+null-terminated string, and is automatically converted into a Lisp
+string when accessed; or if the pointer is C @code{NULL} or @code{0},
+then accessing it gives Lisp @code{nil}.
+
+External format conversion is automatically done when Lisp strings are
+passed to foreign code, or when foreign strings are passed to Lisp code.
+If the type specifier has an explicit @code{external-format}, that
+external format will be used. Otherwise a default external format that
+has been determined at SBCL startup time based on the current locale
+settings will be used. For example, when the following alien routine is
+called, the Lisp string given as argument is converted to an
+@code{ebcdic} octet representation.
+
+@lisp
+(define-alien-routine test int (str (c-string :external-format :ebcdic-us)))
+@end lisp
+
+Lisp strings of type @code{base-string} are stored with a trailing NUL
+termination, so no copying (either by the user or the implementation) is
+necessary when passing them to foreign code, assuming that the
+@code{external-format} and @code{element-type} of the @code{c-string}
+type are compatible with the internal representation of the string. For
+an SBCL built with Unicode support that means an @code{external-format}
+of @code{:ascii} and an @code{element-type} of @code{base-char}. Without
+Unicode support the @code{external-format} can also be
+@code{:iso-8859-1}, and the @code{element-type} can also be
+@code{character}. If the @code{external-format} or @code{element-type}
+is not compatible, or the string is a @code{(simple-array character
+(*))}, this data is copied by the implementation as required.
 
 Assigning a Lisp string to a @code{c-string} structure field or
 variable stores the contents of the string to the memory already
@@ -355,7 +381,7 @@ array type. @code{deref} can be set with @code{setf} to assign a new
 value.
 @end defun
 
-@defun sb-alien:slot @var{struct-or-union} &rest @var{slot-names}
+@defun sb-alien:slot @var{struct-or-union} @var{slot-name}
 @findex slot
 
 The @code{sb-alien:slot} function extracts the value of the slot named
@@ -1182,8 +1208,8 @@ routine, e.g.: @samp{cc -c test.c && ld -shared -o test.so test.o} (In
 order to enable incremental loading with some linkers, you may need to
 say @samp{cc -G 0 -c test.c})
 
-Once the C code has been compiled, you can start up Lisp and load it
-in: @samp{sbcl} Lisp should start up with its normal prompt.
+Once the C code has been compiled, you can start up Lisp and load it in:
+@samp{sbcl}.  Lisp should start up with its normal prompt.
 
 Within Lisp, compile the Lisp file. (This step can be done
 separately. You don't have to recompile every time.)