What’s New


  • ffi.gc(p, None) removes the destructor on an object previously created by another call to ffi.gc()
  • bool(ffi.cast("primitive type", x)) now returns False if the value is zero (including -0.0), and True otherwise. Previously this would only return False for cdata objects of a pointer type when the pointer is NULL.
  • bytearrays: ffi.from_buffer(bytearray-object) is now supported. (The reason it was not supported was that it was hard to do in PyPy, but it works since PyPy 5.3.) To call a C function with a char * argument from a buffer object—now including bytearrays—you write lib.foo(ffi.from_buffer(x)). Additionally, this is now supported: p[0:length] = bytearray-object. The problem with this was that a iterating over bytearrays gives numbers instead of characters. (Now it is implemented with just a memcpy, of course, not actually iterating over the characters.)
  • C++: compiling the generated C code with C++ was supposed to work, but failed if you make use the bool type (because that is rendered as the C _Bool type, which doesn’t exist in C++).
  • help(lib) and help(lib.myfunc) now give useful information, as well as dir(p) where p is a struct or pointer-to-struct.


  • ffi.list_types()
  • ffi.unpack()
  • extern “Python+C”
  • in API mode, lib.foo.__doc__ contains the C signature now. On CPython you can say help(lib.foo), but for some reason help(lib) (or help(lib.foo) on PyPy) is still useless; I haven’t yet figured out the hacks needed to convince pydoc to show more. (You can use dir(lib) but it is not most helpful.)
  • Yet another attempt at robustness of ffi.def_extern() against CPython’s interpreter shutdown logic.


  • Fix 1.5.1 for Python 2.6.


  • A few installation-time tweaks (thanks Stefano!)
  • Issue #245: Win32: __stdcall was never generated for extern "Python" functions
  • Issue #246: trying to be more robust against CPython’s fragile interpreter shutdown logic



Nothing changed from v1.4.1.


  • Fix the compilation failure of cffi on CPython 3.5.0. (3.5.1 works; some detail changed that makes some underscore-starting macros disappear from view of extension modules, and I worked around it, thinking it changed in all 3.5 versions—but no: it was only in 3.5.1.)


  • A better way to do callbacks has been added (faster and more portable, and usually cleaner). It is a mechanism for the out-of-line API mode that replaces the dynamic creation of callback objects (i.e. C functions that invoke Python) with the static declaration in cdef() of which callbacks are needed. This is more C-like, in that you have to structure your code around the idea that you get a fixed number of function pointers, instead of creating them on-the-fly.
  • ffi.compile() now takes an optional verbose argument. When True, distutils prints the calls to the compiler.
  • ffi.compile() used to fail if given sources with a path that includes "..". Fixed.
  • ffi.init_once() added. See docs.
  • dir(lib) now works on libs returned by ffi.dlopen() too.
  • Cleaned up and modernized the content of the demo subdirectory in the sources (thanks matti!).
  • ffi.new_handle() is now guaranteed to return unique void * values, even if called twice on the same object. Previously, in that case, CPython would return two cdata objects with the same void * value. This change is useful to add and remove handles from a global dict (or set) without worrying about duplicates. It already used to work like that on PyPy. This change can break code that used to work on CPython by relying on the object to be kept alive by other means than keeping the result of ffi.new_handle() alive. (The corresponding warning in the docs of ffi.new_handle() has been here since v0.8!)


  • The optional typedefs (bool, FILE and all Windows types) were not always available from out-of-line FFI objects.
  • Opaque enums are phased out from the cdefs: they now give a warning, instead of (possibly wrongly) being assumed equal to unsigned int. Please report if you get a reasonable use case for them.
  • Some parsing details, notably volatile is passed along like const and restrict. Also, older versions of pycparser mis-parse some pointer-to-pointer types like char * const *: the “const” ends up at the wrong place. Added a workaround.


  • Added ffi.memmove().
  • Pull request #64: out-of-line API mode: we can now declare floating-point types with typedef float... foo_t;. This only works if foo_t is a float or a double, not long double.
  • Issue #217: fix possible unaligned pointer manipulation, which crashes on some architectures (64-bit, non-x86).
  • Issues #64 and #126: when using set_source() or verify(), the const and restrict keywords are copied from the cdef to the generated C code; this fixes warnings by the C compiler. It also fixes corner cases like typedef const int T; T a; which would previously not consider a as a constant. (The cdata objects themselves are never const.)
  • Win32: support for __stdcall. For callbacks and function pointers; regular C functions still don’t need to have their calling convention declared.
  • Windows: CPython 2.7 distutils doesn’t work with Microsoft’s official Visual Studio for Python, and I’m told this is not a bug. For ffi.compile(), we removed a workaround that was inside cffi but which had unwanted side-effects. Try saying import setuptools first, which patches distutils...


Nothing changed from v1.2.0.


  • Out-of-line mode: int a[][...]; can be used to declare a structure field or global variable which is, simultaneously, of total length unknown to the C compiler (the a[] part) and each element is itself an array of N integers, where the value of N is known to the C compiler (the int and [...] parts around it). Similarly, int a[5][...]; is supported (but probably less useful: remember that in C it means int (a[5])[...];).
  • PyPy: the lib.some_function objects were missing the attributes __name__, __module__ and __doc__ that are expected e.g. by some decorators-management functions from functools.
  • Out-of-line API mode: you can now do from _example.lib import x to import the name x from _example.lib, even though the lib object is not a standard module object. (Also works in from _example.lib import *, but this is even more of a hack and will fail if lib happens to declare a name called __all__. Note that * excludes the global variables; only the functions and constants make sense to import like this.)
  • lib.__dict__ works again and gives you a copy of the dict—assuming that lib has got no symbol called precisely __dict__. (In general, it is safer to use dir(lib).)
  • Out-of-line API mode: global variables are now fetched on demand at every access. It fixes issue #212 (Windows DLL variables), and also allows variables that are defined as dynamic macros (like errno) or __thread -local variables. (This change might also tighten the C compiler’s check on the variables’ type.)
  • Issue #209: dereferencing NULL pointers now raises RuntimeError instead of segfaulting. Meant as a debugging aid. The check is only for NULL: if you dereference random or dead pointers you might still get segfaults.
  • Issue #152: callbacks: added an argument ffi.callback(..., onerror=...). If the main callback function raises an exception and onerror is provided, then onerror(exception, exc_value, traceback) is called. This is similar to writing a try: except: in the main callback function, but in some cases (e.g. a signal) an exception can occur at the very start of the callback function—before it had time to enter the try: except: block.
  • Issue #115: added ffi.new_allocator(), which officializes support for alternative allocators.


  • ffi.gc(): fixed a race condition in multithreaded programs introduced in 1.1.1


  • Out-of-line mode: ffi.string(), ffi.buffer() and ffi.getwinerror() didn’t accept their arguments as keyword arguments, unlike their in-line mode equivalent. (It worked in PyPy.)
  • Out-of-line ABI mode: documented a restriction of ffi.dlopen() when compared to the in-line mode.
  • ffi.gc(): when called several times with equal pointers, it was accidentally registering only the last destructor, or even none at all depending on details. (It was correctly registering all of them only in PyPy, and only with the out-of-line FFIs.)


  • Out-of-line API mode: we can now declare integer types with typedef int... foo_t;. The exact size and signedness of foo_t is figured out by the compiler.
  • Out-of-line API mode: we can now declare multidimensional arrays (as fields or as globals) with int n[...][...]. Before, only the outermost dimension would support the ... syntax.
  • Out-of-line ABI mode: we now support any constant declaration, instead of only integers whose value is given in the cdef. Such “new” constants, i.e. either non-integers or without a value given in the cdef, must correspond to actual symbols in the lib. At runtime they are looked up the first time we access them. This is useful if the library defines extern const sometype somename;.
  • ffi.addressof(lib, "func_name") now returns a regular cdata object of type “pointer to function”. You can use it on any function from a library in API mode (in ABI mode, all functions are already regular cdata objects). To support this, you need to recompile your cffi modules.
  • Issue #198: in API mode, if you declare constants of a struct type, what you saw from lib.CONSTANT was corrupted.
  • Issue #196: ffi.set_source("package._ffi", None) would incorrectly generate the Python source to package._ffi.py instead of package/_ffi.py. Also fixed: in some cases, if the C file was in build/foo.c, the .o file would be put in build/build/foo.o.


  • Same as 1.0.2, apart from doc and test fixes on some platforms.


  • Variadic C functions (ending in a ”...” argument) were not supported in the out-of-line ABI mode. This was a bug—there was even a (non-working) example doing exactly that!


  • ffi.set_source() crashed if passed a sources=[..] argument. Fixed by chrippa on pull request #60.
  • Issue #193: if we use a struct between the first cdef() where it is declared and another cdef() where its fields are defined, then this definition was ignored.
  • Enums were buggy if you used too many ”...” in their definition.


  • The main news item is out-of-line module generation:
  • (this page will list what is new from all versions from 1.0.0 forward.)