--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2012-05-13  Bruno Haible  <bruno@clisp.org>
+	    Paul Eggert  <eggert@cs.ucla.edu>
+
+	binary-io: Define set_binary_mode function.
+	* lib/binary-io.h (set_binary_mode): New function.
+	(SET_BINARY): Define in terms of set_binary_mode.
+	* modules/binary-io (configure.ac): Require AC_C_INLINE.
+	* tests/test-binary-io.c (main): Accept an argument, and test either
+	set_binary_mode or SET_BINARY depending on the argument.
+	* tests/test-binary-io.sh: Invoke test-binary-io twice, with an
+	argument. Clean up also t-bin-out0.tmp.
+
 2012-05-13  Stefano Lattarini  <stefano.lattarini@gmail.com>
 
 	bootstrap: take advantage of POSIX shell features

--- a/lib/binary-io.h
+++ b/lib/binary-io.h
@@ -25,28 +25,41 @@
    so we include it here first.  */
 #include <stdio.h>
 
-/* SET_BINARY (fd);
-   changes the file descriptor fd to perform binary I/O.  */
+/* set_binary_mode (fd, mode)
+   sets the binary/text I/O mode of file descriptor fd to the given mode
+   (must be O_BINARY or O_TEXT) and returns the previous mode.  */
 #if O_BINARY
 # if defined __EMX__ || defined __DJGPP__ || defined __CYGWIN__
 #  include <io.h> /* declares setmode() */
+#  define set_binary_mode setmode
 # else
-#  define setmode _setmode
+#  define set_binary_mode _setmode
 #  undef fileno
 #  define fileno _fileno
 # endif
-# ifdef __DJGPP__
-#  include <unistd.h> /* declares isatty() */
-   /* Avoid putting stdin/stdout in binary mode if it is connected to
-      the console, because that would make it impossible for the user
-      to interrupt the program through Ctrl-C or Ctrl-Break.  */
-#  define SET_BINARY(fd) ((void) (!isatty (fd) ? (setmode (fd, O_BINARY), 0) : 0))
-# else
-#  define SET_BINARY(fd) ((void) setmode (fd, O_BINARY))
-# endif
 #else
-  /* On reasonable systems, binary I/O is the default.  */
-# define SET_BINARY(fd) /* do nothing */ ((void) 0)
+  /* On reasonable systems, binary I/O is the only choice.  */
+  /* Use an inline function rather than a macro, to avoid gcc warnings
+     "warning: statement with no effect".  */
+static inline int
+set_binary_mode (int fd, int mode)
+{
+  (void) fd;
+  (void) mode;
+  return O_BINARY;
+}
+#endif
+
+/* SET_BINARY (fd);
+   changes the file descriptor fd to perform binary I/O.  */
+#ifdef __DJGPP__
+# include <unistd.h> /* declares isatty() */
+  /* Avoid putting stdin/stdout in binary mode if it is connected to
+     the console, because that would make it impossible for the user
+     to interrupt the program through Ctrl-C or Ctrl-Break.  */
+# define SET_BINARY(fd) ((void) (!isatty (fd) ? (set_binary_mode (fd, O_BINARY), 0) : 0))
+#else
+# define SET_BINARY(fd) ((void) set_binary_mode (fd, O_BINARY))
 #endif
 
 #endif /* _BINARY_H */

--- a/modules/binary-io
+++ b/modules/binary-io
@@ -8,6 +8,7 @@
 fcntl-h
 
 configure.ac:
+AC_REQUIRE([AC_C_INLINE])
 
 Makefile.am:
 lib_SOURCES += binary-io.h

--- a/tests/test-binary-io.c
+++ b/tests/test-binary-io.c
@@ -30,26 +30,40 @@
 #include "macros.h"
 
 int
-main ()
+main (int argc, char *argv[])
 {
   /* Test the O_BINARY macro.  */
   {
     int fd =
-      open ("t-bin-out2.tmp", O_CREAT | O_TRUNC | O_RDWR | O_BINARY, 0600);
+      open ("t-bin-out0.tmp", O_CREAT | O_TRUNC | O_RDWR | O_BINARY, 0600);
     if (write (fd, "Hello\n", 6) < 0)
       exit (1);
     close (fd);
   }
   {
     struct stat statbuf;
-    if (stat ("t-bin-out2.tmp", &statbuf) < 0)
+    if (stat ("t-bin-out0.tmp", &statbuf) < 0)
       exit (1);
     ASSERT (statbuf.st_size == 6);
   }
 
-  /* Test the SET_BINARY macro.  */
-  SET_BINARY (1);
-  fputs ("Hello\n", stdout);
+  switch (argv[1][0])
+    {
+    case '1':
+      /* Test the set_binary_mode() function.  */
+      set_binary_mode (1, O_BINARY);
+      fputs ("Hello\n", stdout);
+      break;
+
+    case '2':
+      /* Test the SET_BINARY macro.  */
+      SET_BINARY (1);
+      fputs ("Hello\n", stdout);
+      break;
+
+    default:
+      break;
+    }
 
   return 0;
 }

--- a/tests/test-binary-io.sh
+++ b/tests/test-binary-io.sh
@@ -3,9 +3,11 @@
 tmpfiles=""
 trap 'rm -fr $tmpfiles' 1 2 3 15
 
-tmpfiles="$tmpfiles t-bin-out1.tmp t-bin-out2.tmp"
-./test-binary-io${EXEEXT} > t-bin-out1.tmp || exit 1
-cmp t-bin-out1.tmp t-bin-out2.tmp > /dev/null || exit 1
+tmpfiles="$tmpfiles t-bin-out0.tmp t-bin-out1.tmp t-bin-out2.tmp"
+./test-binary-io${EXEEXT} 1 > t-bin-out1.tmp || exit 1
+cmp t-bin-out0.tmp t-bin-out1.tmp > /dev/null || exit 1
+./test-binary-io${EXEEXT} 2 > t-bin-out2.tmp || exit 1
+cmp t-bin-out0.tmp t-bin-out2.tmp > /dev/null || exit 1
 
 rm -fr $tmpfiles