Author: Armin Rigo <ar...@tunes.org>
Branch:
Changeset: r3010:62beffad167e
Date: 2017-09-15 19:24 +0200
http://bitbucket.org/cffi/cffi/changeset/62beffad167e/
Log: Update the doc, as suggested on python-cffi
diff --git a/doc/source/using.rst b/doc/source/using.rst
--- a/doc/source/using.rst
+++ b/doc/source/using.rst
@@ -128,10 +128,37 @@
There is no general equivalent to the ``&`` operator in C (because it
would not fit nicely in the model, and it does not seem to be needed
-here). But see `ffi.addressof()`__.
+here). There is `ffi.addressof()`__, but only for some cases. You
+cannot take the "address" of a number in Python, for example; similarly,
+you cannot take the address of a CFFI pointer. If you have this kind
+of C code::
+
+ int x, y;
+ fetch_size(&x, &y);
+
+ opaque_t *handle; // some opaque pointer
+ init_stuff(&handle); // initializes the variable 'handle'
+ more_stuff(handle); // pass the handle around to more functions
+
+then you need to rewrite it like this, replacing the variables in C
+with what is logically pointers to the variables:
+
+.. code-block:: python
+
+ px = ffi.new("int *")
+ py = ffi.new("int *") arr = ffi.new("int[2]")
+ lib.fetch_size(px, py) -OR- lib.fetch_size(arr, arr + 1)
+ x = px[0] x = arr[0]
+ y = py[0] y = arr[1]
+
+ p_handle = ffi.new("opaque_t **")
+ lib.init_stuff(p_handle) # pass the pointer to the 'handle' pointer
+ handle = p_handle[0] # now we can read 'handle' out of 'p_handle'
+ lib.more_stuff(handle)
.. __: ref.html#ffi-addressof
+
Any operation that would in C return a pointer or array or struct type
gives you a fresh cdata object. Unlike the "original" one, these fresh
cdata objects don't have ownership: they are merely references to
@@ -208,7 +235,7 @@
string stored in the source array (adding surrogates if necessary).
See the `Unicode character types`__ section for more details.
-__: ref.html#unichar
+.. __: ref.html#unichar
Note that unlike Python lists or tuples, but like C, you *cannot* index in
a C array from the end using negative numbers.
_______________________________________________
pypy-commit mailing list
pypy-commit@python.org
https://mail.python.org/mailman/listinfo/pypy-commit
