从JNA调用读取String[]失败

Question

根据文件，结构如下：

char*GR_NAME

组的名称。

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Platform;

public class Test {

    public interface CLibrary extends Library {
            CLibrary INSTANCE = (CLibrary)  Native.loadLibrary((Platform.isWindows() ? "msvcrt" : "c"), CLibrary.class);

            void printf(String format, Object... args);

            public Group getgrnam(String groupName);
        }


        public static void main(String[] args) {
            CLibrary.INSTANCE.printf("Hello, World\n");

            Group group = CLibrary.INSTANCE.getgrnam(args[0]);

            System.out.println(group.gr_name);
            System.out.println(group.gr_mem);

        }
    }

import java.util.ArrayList;
import java.util.List;

import com.sun.jna.Structure;

public class Group extends Structure {
    public String gr_name;
    public int gr_gid;
    public String[] gr_mem = new String[128];

    @Override
    protected List<String> getFieldOrder() {
        List<String> fields = new ArrayList<>();
        fields.add("gr_name");
        fields.add("gr_gid");
        fields.add("gr_mem");
        return fields;
    }
}

/tmp#java-cp.：jna-4.5.1.jar测试root Hello,线程“main”java.lang.IllegalArgumentException：在com.sun.jna.pointer.ReadArray（pointer.java:538)在com.sun.jna.pointer.GetValue（pointer.java:459)在com.sun.jna.structure.ReadField（structure.java:720)在com.sun.jna.structure.Read（structure.java:580)java:550)在com.sun.jna.function.invoke（function.java:446)在com.sun.jna.function.invoke（function.java:354)在com.sun.jna.library$handler.invoke（library.java:244)在com.sun.proxy.$proxy0.getgrnam（未知来源）在Test.main(Test.java:23)

如何正确转换Char**的结构字段？

Answer 1

自我回答，因为我在挖掘后发现了它。

主要突破是这个工具:https://github.com/nativelibs4java/jnaerator

它从C结构生成Java类，这很有帮助！

import com.sun.jna.Pointer;
import com.sun.jna.Structure;
import com.sun.jna.ptr.PointerByReference;
import java.util.Arrays;
import java.util.List;
/**
 * <i>native declaration : line 2</i><br>
 * This file was autogenerated by <a href="http://jnaerator.googlecode.com/">JNAerator</a>,<br>
 * a tool written by <a href="http://ochafik.com/">Olivier Chafik</a> that <a href="http://code.google.com/p/jnaerator/wiki/CreditsAndLicense">uses a few opensource projects.</a>.<br>
 * For help, please visit <a href="http://nativelibs4java.googlecode.com/">NativeLibs4Java</a> , <a href="http://rococoa.dev.java.net/">Rococoa</a>, or <a href="http://jna.dev.java.net/">JNA</a>.
 */
public class Group extends Structure {
  /**
   * Group name.<br>
   * C type : char*
   */
  public Pointer gr_name;
  /**
   * Password.<br>
   * C type : char*
   */
  public Pointer gr_passwd;
  /**
   * Group ID.<br>
   * C type : __gid_t
   */
  public int gr_gid;
  /**
   * Member list.<br>
   * C type : char**
   */
  public PointerByReference gr_mem;
  public Group() {
    super();
  }
  protected List<String> getFieldOrder() {
    return Arrays.asList("gr_name", "gr_passwd", "gr_gid", "gr_mem");
  }
  /**
   * @param gr_name Group name.<br>
   * C type : char*<br>
   * @param gr_passwd Password.<br>
   * C type : char*<br>
   * @param gr_gid Group ID.<br>
   * C type : __gid_t<br>
   * @param gr_mem Member list.<br>
   * C type : char**
   */
  public Group(Pointer gr_name, Pointer gr_passwd, int gr_gid, PointerByReference gr_mem) {
    super();
    this.gr_name = gr_name;
    this.gr_passwd = gr_passwd;
    this.gr_gid = gr_gid;
    this.gr_mem = gr_mem;
  }
  public Group(Pointer peer) {
    super(peer);
  }
  protected ByReference newByReference() { return new ByReference(); }
  protected ByValue newByValue() { return new ByValue(); }
  protected Group newInstance() { return new Group(); }
//  public static Group[] newArray(int arrayLength) {
//    return Structure.newArray(Group.class, arrayLength);
//  }
  public static class ByReference extends Group implements Structure.ByReference {

  };
  public static class ByValue extends Group implements Structure.ByValue {

  };
}

  public static void main(String[] args) {

    Group group = CLibrary.INSTANCE.getgrnam(args[0]);
    System.out.println(group.gr_name.getString(0));

    PointerByReference pbr = group.gr_mem;
    String[] groups = pbr.getPointer().getStringArray(0);

    for (String g : groups) {
      System.out.println(g);
    }