Re: [Factor-talk] Output parameters in alien
After investigating a bit, it might be possible? If someone more
knowledgeable about the ffi could comment on the following:
FUNCTION: char* strcpy ( char * , c-string ) ;
: foo ( -- ) { { { char 2 } initial: B{ 0x41 0 } } } [ "B" strcpy drop ]
with-out-parameters utf8 alien>string print ;
: bar ( -- ) { { { char 2 } initial: B{ 0x41 0 } } } [ drop ]
with-out-parameters utf8 alien>string print ;
foo ! prints "B"
bar ! prints "A"
If there is no syntactic sugar yet for passing strings with
with-out-parameters, it might be interesting to add it I guess
PS: typed this manually, sorry if there are typos :)
Jon
Le 28 nov. 2014 20:43, "Jon Harper" a écrit :
> John provided an alternative, but here are the explanations of the errors
> you got:
>
> On Fri, Nov 28, 2014 at 5:14 PM, Andrea Ferretti > wrote:
>
>> { { c-string } } [ "hello world" swap example_cp ] with-out-parameters
>>
> The syntax of with-out-parameters is an array of elements, which are
> either a c-type, or a triple { c-type intial: value }. So in your case, it
> should have been
> { c-string } [ "hello world" swap example_cp ] with-out-parameters
>
> I get "index out of bounds: 0" which seems reasonable, since I pass an
>> empty c-string. But if I try something like
>>
>> { { c-string initial: "hello earth" } } [ "hello world" swap
>> example_cp ] with-out-parameters
>>
>> I get "local-allocation-error".
>>
> The FFI only works with the optimizing compiler, so this code should be
> defined in a word, not run in the interactive listener. You can define the
> word in a source file, or directly in the listener and then call it just
> after you defined it
>
>
> Cheers,
> Jon
>
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Re: [Factor-talk] Output parameters in alien
John provided an alternative, but here are the explanations of the errors
you got:
On Fri, Nov 28, 2014 at 5:14 PM, Andrea Ferretti
wrote:
> { { c-string } } [ "hello world" swap example_cp ] with-out-parameters
>
The syntax of with-out-parameters is an array of elements, which are either
a c-type, or a triple { c-type intial: value }. So in your case, it should
have been
{ c-string } [ "hello world" swap example_cp ] with-out-parameters
I get "index out of bounds: 0" which seems reasonable, since I pass an
> empty c-string. But if I try something like
>
> { { c-string initial: "hello earth" } } [ "hello world" swap
> example_cp ] with-out-parameters
>
> I get "local-allocation-error".
>
The FFI only works with the optimizing compiler, so this code should be
defined in a word, not run in the interactive listener. You can define the
word in a source file, or directly in the listener and then call it just
after you defined it
Cheers,
Jon
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Re: [Factor-talk] Output parameters in alien
I think you won't be able to use with-out-parameters which seems to work
really well with value types, but maybe not so well for your example. Part
of the problem might be the way c-string automatically encodes and decodes
using your encoding (utf8 by default I think). Factor strings are not the
same as char*, so they have have to be converted into and out of "raw
memory" using an encoding when calling functions that take c-strings.
Here's an example using strcpy for convenience, and raw memory (using char*
instead of c-string). We will try and preserve the dst input pointer
instead of using the return value.
FUNCTION: char* strcpy ( char* dst, char* src ) ;
We will make a word that takes a Factor string, encodes it into a utf8
byte-array, allocates a new byte-array destination, then calls strcpy,
drops the return value, and uses the destination byte-array to decode back
into a Factor string.
: do-strcpy ( src -- dst )
utf8 string>alien
[ length dup ] [ strcpy drop ] bi
utf8 alien>string ;
IN: scratchpad "hello" do-strcpy .
"hello"
You can use byte-arrays, or raw memory allocated with malloc (make sure to
&free with destructors, or free manually).
On Fri, Nov 28, 2014 at 8:14 AM, Andrea Ferretti
wrote:
> I am trying to interface with C code. Everything seems to work more or
> less fine, until I have to deal with output parameters, that is,
> parameters in C functions which are meant to be passed buffers which
> are filled by the function.
>
> I have made a very basic example which only copies a string and I have
> made a shared library called "libexample.so" which exports
>
> void example_cp(char *in, char *out);
>
> I have verified that I can call the shared library from C.
>
> Now in factor I have defined an interface like this
>
> USING: alien alien.c-types alien.syntax alien.libraries ;
> IN: example-alien
>
> <<
> "libexample" "/home/papillon/esperimenti/ssl/libexample.so" cdecl
> add-library
> >>
>
> LIBRARY: libexample
> FUNCTION: void example_cp ( c-string in, c-string out ) ;
>
> In the listener I try to use example_cp, but I am not sure how to pass
> a preallocated char buffer. If I try
>
> { { c-string } } [ "hello world" swap example_cp ] with-out-parameters
>
> I get "index out of bounds: 0" which seems reasonable, since I pass an
> empty c-string. But if I try something like
>
> { { c-string initial: "hello earth" } } [ "hello world" swap
> example_cp ] with-out-parameters
>
> I get "local-allocation-error".
>
> What is the correct way to pass a preallocated buffer?
>
>
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[Factor-talk] Output parameters in alien
I am trying to interface with C code. Everything seems to work more or
less fine, until I have to deal with output parameters, that is,
parameters in C functions which are meant to be passed buffers which
are filled by the function.
I have made a very basic example which only copies a string and I have
made a shared library called "libexample.so" which exports
void example_cp(char *in, char *out);
I have verified that I can call the shared library from C.
Now in factor I have defined an interface like this
USING: alien alien.c-types alien.syntax alien.libraries ;
IN: example-alien
<<
"libexample" "/home/papillon/esperimenti/ssl/libexample.so" cdecl
add-library
>>
LIBRARY: libexample
FUNCTION: void example_cp ( c-string in, c-string out ) ;
In the listener I try to use example_cp, but I am not sure how to pass
a preallocated char buffer. If I try
{ { c-string } } [ "hello world" swap example_cp ] with-out-parameters
I get "index out of bounds: 0" which seems reasonable, since I pass an
empty c-string. But if I try something like
{ { c-string initial: "hello earth" } } [ "hello world" swap
example_cp ] with-out-parameters
I get "local-allocation-error".
What is the correct way to pass a preallocated buffer?
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