How can I get the Pointer for a native library in JNA?

Question

I want to reproduce this sample code in JNA : http://msdn.microsoft.com/en-us/library/windows/desktop/bb427356%28v=vs.85%29.aspx

In this code, I have to use the FormatMessage function (in Kernel32). I can have access to this function through JNA, but the second param is a pointer / handle on the return value of the call of LoadLibraryEx.

Here is the question : how can I fill the ??????? :

Pointer p = ???????
String m = Kernel32.INSTANCE.FormatMessage(flag, p, .....)

Thanks for any help.

loshad vtapkah · Accepted Answer · 2014-12-02 20:20:13Z

1

You need to call LoadLibraryEx(). This is how I call a function returning a pointer (actually a String, but I work with it as a Pointer to be able to free the memory):

public interface CLibrary1 extends Library
{
    public Pointer string_test(String str1, String str2); 
}

public static void main(String[] args)
{
    try {
        CLibrary1 clib1 = (CLibrary1)Native.loadLibrary("???.so", CLibrary1.class);
        Pointer p = clib1.string_test("string1", "string3");
        System.out.println(p.getString(0));
        Native.free(Pointer.nativeValue(p));
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

This example calls the function char* string_test(char *, char *);

answered Dec 2, 2014 at 20:20

loshad vtapkah

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2 Comments

iXô Over a year ago

Do you mean to add the LoadLibraryEx function definition into the JNA libraries interface to call it ?

loshad vtapkah Over a year ago

Yes. FormatMessage() function expects the memory area with data filled by LoadLibraryEx(), so you need to call it as any other external function.

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