Returning and accessing array of object of structure in jna

问题

I have a structure that contains some char pointers in C:

struct inputsheet
{
    char* TestCaseID[MAX_TEST_CASES];
    char*  Description[MAX_TEST_CASES];
};

I have a function that is returns array of object of structure:

struct inputsheet* getapi(char *docname);

Now I want to use this in Java. How can I handle this array of object of structure? I am able to handle a single object but not the array.

For single object my code in C is here:

public class str3 extends com.sun.jna.Structure implements com.sun.jna.Structure.ByReference {  
   public Pointer a1;
   public Pointer b2;
   public Pointer c3[]=new Pointer[10];
}

Accessing it:

str2 s2=CLibrary.INSTANCE.parseid(xmlFile1);
for(Pointer p1:s2.testCaseID) {
    if(p1!=null)
    {
        System.out.println(p1.getString(0));
    }
}

EDIT

\\c code
struct str3{
char *a;
char *b;
char *ab[10];
}

\\jna implementation


package parser;
import com.sun.jna.Pointer;
public class str3 extends com.sun.jna.Structure implements     com.sun.jna.Structure.ByReference{ 
public Pointer a1;
public Pointer b2;
public Pointer c3[]=new Pointer[10];
}


\\calling it
import com.sun.jna.Native;
import com.sun.jna.Pointer;
 class ab{
    interface CLibrary extends Library{
    CLibrary INSTANCE = (CLibrary) Native.loadLibrary("chardll",
    CLibrary.class);
    str3 getStruct();
    }

public static void main(String[] args) {
    int size = 5;
    str3 a=CLibrary.INSTANCE.getStruct();
    str3[] ab=(str3[])a.toArray(size);
    System.out.println(ab[0].a1.getString(0));          
    }
}

It is giving Garbage value as output,, where I have to update my code to get the right output..

回答1:

From the javadoc:

Returning an Array of struct

Declare the method as returning a Structure of the appropriate type, then invoke Structure.toArray(int) to convert to an array of initialized structures of the appropriate size. Note that your Structure class must have a no-args constructor, and you are responsible for freeing the returned memory if applicable in whatever way is appropriate for the called function.
// Original C code
struct Display* get_displays(int* pcount);
void free_displays(struct Display* displays);

// Equivalent JNA mapping
Display get_displays(IntByReference pcount);
void free_displays(Display[] displays);
...
IntByReference pcount = new IntByReference();
Display d = lib.get_displays(pcount);
Display[] displays = (Display[])d.toArray(pcount.getValue());
...
lib.free_displays(displays);

EDIT

Nominally, your structure would look like this (based on your native definition):

class inputsheet extends Structure {
    public Pointer[] TestCaseID = new Pointer[MAX_TEST_CASES];
    public Pointer[] Description = new Pointer[MAX_TEST_CASES];
}

public inputsheet getapi(String docname);

int size = ...; // whatever you do to figure out the size of your returned array 
inputsheet sheet = INSTANCE.getapi("some-doc");
inputsheet[] sheets = (inputsheet[])sheet.toArray(size);

If the caller doesn't need to write to the inputsheet fields, you should use String instead of Pointer.

来源：https://stackoverflow.com/questions/15430260/returning-and-accessing-array-of-object-of-structure-in-jna

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java

jna