[Ecls-list] FFI and null C strings

Juan Jose Garcia Ripoll lisp at arrakis.es
Wed Nov 24 07:27:46 UTC 2004

Goffioul Michael wrote:

>I found an annoying problem while fixing FFI issues. This is related
>to null C strings. One example is for example:
>(ffi:def-function ("getenv" c-getenv)
>  ((name :cstring))
>  :returning cstring)
>If the variable doesn't exist, "getenv" returns NULL. However, the
>generated C code convert the returned value to a LISP string using
>make_string_copy, which doesn't support NULL as input argument.
>Would it be OK to change make_string_copy such that it returns NIL
>when the input is NULL?
Does this issue pop very often? I do not remember many functions which 
return a null pointer as a string. However, if this is so often that it 
might be worth using, then I would vote for a new function 
ecl_cstring_to_string_or_nil() The name is more clear and it does not 
pervert an existing function which eventually should be replaced by a 
ecl_string_to_string() that fails for NULL pointers.


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