Add vararg demo

2 files changed, 65 insertions, 1 deletions

diff --git a/demo/extern_python_varargs.py b/demo/extern_python_varargs.py
new file mode 100644
index 0000000..ee78079
--- /dev/null
+++ b/demo/extern_python_varargs.py
@@ -0,0 +1,61 @@
+import cffi
+
+ffi = cffi.FFI()
+
+ffi.cdef("""
+    int my_algo(int);
+    typedef ... va_list;
+    extern "Python" int f(int, va_list *);
+
+    int fetch_int(va_list *);
+    double fetch_double(va_list *);
+    void *fetch_ptr(va_list *);
+""")
+
+ffi.set_source("_extern_python_cffi", """
+    #include <stdarg.h>
+
+    static int f(int, va_list *);
+
+    static int f1(int n, ...)
+    {
+        va_list ap;
+        va_start(ap, n);
+        int res = f(n, &ap);
+        va_end(ap);
+        return res;
+    }
+
+    static int fetch_int(va_list *va) { return va_arg((*va), int); }
+    static double fetch_double(va_list *va) { return va_arg((*va), double); }
+    static void * fetch_ptr(va_list *va) { return va_arg((*va), void *); }
+    
+    static int my_algo(int n) {
+        return f1(3, n, n+1, n+2) + f1(1, &n) + f1(2, 12.3, 45.6);
+    }
+""")
+
+ffi.compile()
+
+
+from _extern_python_cffi import ffi, lib
+
+@ffi.def_extern()
+def f(n, va):
+    if n == 3:
+        x = lib.fetch_int(va)
+        y = lib.fetch_int(va)
+        z = lib.fetch_int(va)
+        print (x, y, z)
+    elif n == 1:
+        ptr = lib.fetch_ptr(va)
+        print 'ptr to:', ffi.cast("int *", ptr)[0]
+    elif n == 2:
+        x = lib.fetch_double(va)
+        y = lib.fetch_double(va)
+        print (x, y)
+    else:
+        raise AssertionError(n)
+    return 14
+
+print lib.my_algo(10)
diff --git a/doc/source/using.rst b/doc/source/using.rst
index e45bb63..1c5430c 100644
--- a/doc/source/using.rst
+++ b/doc/source/using.rst
@@ -616,7 +616,10 @@ functions::
     }
 
 The ``extern "Python"`` functions cannot be variadic for now.  This
-may be implemented in the future.
+may be implemented in the future.  (`This demo`__ shows how to do it
+anyway, but it is a bit lengthy.)
+
+.. __: https://bitbucket.org/cffi/cffi/src/default/demo/extern_python_varargs.py
 
 Each corresponding Python callback function is defined with the
 ``@ffi.def_extern()`` decorator.  Be careful when writing this