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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