Pass InputStream through JNA to C code as a File Pointer
c, file-io, java, jna
Solution
I don't believe you can do this - you have no easy way to access the internals of of an `InputStream` instance, and even a `FileInputStream` will most likely not be implemented on top of a stdio FILE *. To see what your Java interface should be like, you'll need to post more about the `foo` function - what it does and how you use it.
If you don't care about what the `FILE *` actually does, you can code up using JNA to call `fopen`, passing in the file name and open mode, and pass the result as an opaque value through to `foo`, e.g. (pseudocode):
path = "MyFile.txt";
bar = Libc.fopen(path, "r");
Libfoo.foo(bar);
Update: If you need to have a string which contains data which you need treated as if it were in a file, I think you are out of luck. Unfortunately, the standard C library is not built on top of a stream abstraction, which means that you are unlikely to be able to achieve what you want unless you can open what looks like a filename but leads to your string data; however, it's going to be much, much easier to bite the bullet and save the string to a temporary file, then open that with `fopen` :-(
Problem
I've got a DLL written in C (that I can't edit) that has some function prototype that looks like ``` #include <stdio.h> void foo(FILE *bar); ``` I'd like to create a JNA interface to the DLL and it's unclear what I need to pass for the FILE *bar argument. I assume I need to pass an InputStream (which is my preference), but the JNA literature seems sparse on the subject. What would the Java interface look like? and what do I really need to pass to foo? Edit: foo assumes bar is the result of an fopen and calls operations like fscanf. Edit 2: Ultimately, I have a string in Java that I need to read in C as if it were a file, (which might be a different question altogether). Ideally I'd like to avoid writing the file, which is why converting an InputStream to a C file pointer is so desirable (and evidently quite difficult).