JNA: How to access array of struct in struct? - arrays

Question

I'm trying to access an array of struct inside a struct. This is the relevant C code reduced to the problem:
typedef struct {
int a;
int b;
} fileinfo_t;
typedef struct {
fileinfo_t **file;
int max_files;
} project_t;
In C accessing the array is as easy as this:
int var_a_of_file_0 = project.file[0].a;
int var_b_of_file_1 = project.file[1].b;
How do I implement this in Java? I'm asking this question because I'm new to JNA. So far I read the JNA documentation and tried every example which is somehow related to my problem but with no luck...
I used JNAerator for converting the header file. I don't know for shure if the result is correct:
package test;
import com.ochafik.lang.jnaerator.runtime.LibraryExtractor;
import com.ochafik.lang.jnaerator.runtime.MangledFunctionMapper;
import com.ochafik.lang.jnaerator.runtime.Structure;
import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.NativeLibrary;
import com.sun.jna.ptr.PointerByReference;
/**
* JNA Wrapper for library <b>test</b><br>
* This file was autogenerated by JNAerator,<br>
* a tool written by Olivier Chafik that uses a few opensource projects..<br>
* For help, please visit NativeLibs4Java , Rococoa, or JNA.
*/
public interface TestLibrary extends Library {
public static final java.lang.String JNA_LIBRARY_NAME = LibraryExtractor.getLibraryPath("test", true, test.TestLibrary.class);
public static final NativeLibrary JNA_NATIVE_LIB = NativeLibrary.getInstance(test.TestLibrary.JNA_LIBRARY_NAME, com.ochafik.lang.jnaerator.runtime.MangledFunctionMapper.DEFAULT_OPTIONS);
public static final TestLibrary INSTANCE = (TestLibrary)Native.loadLibrary(test.TestLibrary.JNA_LIBRARY_NAME, test.TestLibrary.class, com.ochafik.lang.jnaerator.runtime.MangledFunctionMapper.DEFAULT_OPTIONS);
public static class fileinfo_t extends Structure<fileinfo_t, fileinfo_t.ByValue, fileinfo_t.ByReference > {
public int a;
public int b;
public fileinfo_t() {
super();
}
public fileinfo_t(int a, int b) {
super();
this.a = a;
this.b = b;
}
protected ByReference newByReference() { return new ByReference(); }
protected ByValue newByValue() { return new ByValue(); }
protected fileinfo_t newInstance() { return new fileinfo_t(); }
public static fileinfo_t[] newArray(int arrayLength) {
return Structure.newArray(fileinfo_t.class, arrayLength);
}
public static class ByReference extends fileinfo_t implements Structure.ByReference {
};
public static class ByValue extends fileinfo_t implements Structure.ByValue {
};
};
public static class project_t extends Structure<project_t, project_t.ByValue, project_t.ByReference > {
/// C type : fileinfo_t**
public PointerByReference file;
public int max_files;
public project_t() {
super();
}
/// #param file C type : fileinfo_t**
public project_t(PointerByReference file, int max_files) {
super();
this.file = file;
this.max_files = max_files;
}
protected ByReference newByReference() { return new ByReference(); }
protected ByValue newByValue() { return new ByValue(); }
protected project_t newInstance() { return new project_t(); }
public static project_t[] newArray(int arrayLength) {
return Structure.newArray(project_t.class, arrayLength);
}
public static class ByReference extends project_t implements Structure.ByReference {
};
public static class ByValue extends project_t implements Structure.ByValue {
};
};
}
Any help would be appreciated.

Answer 1

Since the array of structs does not overlay the containing struct's memory, you need a Pointer or equivalent type for that field. You can then manually derive the structure you need from the base pointer.
I don't think your usage example is valid, however.
Once you index with "[0]", you have a pointer to fileinfo_t, so you would have to use the following (have you actually compiled your example in C?):
int var_a_of_file_0 = project.file[0]->a;
int var_b_of_file_1 = project.file[1]->b;
Ultimately how you extract the actual structures depends on how they are laid out in memory, which is ambiguous in your current explanation.