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Diffstat (limited to 'doc/source/using.rst')
| -rw-r--r-- | doc/source/using.rst | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/doc/source/using.rst b/doc/source/using.rst index 38c96ba..ccaa4db 100644 --- a/doc/source/using.rst +++ b/doc/source/using.rst @@ -383,6 +383,18 @@ argument and may mutate it!): assert lib.strlen("hello") == 5 +(Note that there is no guarantee that the ``char *`` passed to the +function remains valid after the call is done. Similarly, if you write +``lib.f(x); lib.f(x)`` where ``x`` is a variable containing a byte string, +the two calls to ``f()`` could sometimes receive different ``char *`` +pointers, with each of them only valid during the corresponding call. This is +important notably for PyPy which uses many optimizations tweaking the data +underlying a byte string object. CFFI will not make and free a copy of +the whole string at *every* call---it usually won't---but you *cannot* +write code that relies on it: there are cases were that would break. +If you need a pointer to remain valid, you need to make one explicitly, +for example with ``ptr = ffi.new("char[]", x)``.) + You can also pass unicode strings as ``wchar_t *`` or ``char16_t *`` or ``char32_t *`` arguments. Note that the C language makes no difference between argument declarations that |