char *的一个bug？有不同顺序时产生-优快云博客

本文链接：https://blog.youkuaiyun.com/skzr_org/article/details/83709247

本文探讨了在使用Java Native Interface (JNI)进行Java与C/C++混合编程时遇到的问题，特别是关于rf_select3方法的参数传递错误导致的问题。通过调整Java端的方法签名，从使用long类型改为使用NativeLong类型，解决了C++端指针操作引发的错误。

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Thanks for your help :)

windows xp x86, jdk 1.6.20

hellojna dll project

hellojna.h

extern "C" _declspec(dllexport) int swapvalue(int* a, int* b);
extern "C" _declspec(dllexport) int rf_select1(unsigned char *_Size);
extern "C" _declspec(dllexport) int rf_select2(unsigned char *_Size,long icdev);
extern "C" _declspec(dllexport) int rf_select3(long icdev, unsigned char *_Size);

hellojna.cpp

#include "stdafx.h"
#include "hellojna.h"

int rf_select1(unsigned char *_Size) {
    _Size[0] = 'a';
    return 12;
}

int rf_select2(unsigned char *_Size, long icdev) {
    _Size[0] = 'a';
    return 12;
}

int rf_select3(long icdev, unsigned char *_Size) {
    _Size[0] = 'a';
    return 12;
}

HelloJna.java

public interface HelloJna extends Library {
	HelloJna instance = (HelloJna) Native.loadLibrary("hellojna", HelloJna.class);
	int rf_select1(byte[] abd);
	int rf_select2(byte[] abd, long dev);
	int rf_select3(long dev, byte[] abd);
}

Test.java

public class Test {
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		HelloJna jna = HelloJna.instance;

		byte[] buf = new byte[]{'s', 'u', 'p', 'e', 'r', ' ', 'm', 'a', 'n', '\0'};
		int ret = jna.rf_select1(buf);
		System.out.println("buf=" + new String(buf) + ",ret=" + ret);
		
		buf[0] = 'I';
		ret = jna.rf_select2(buf, 77);
		System.out.println("77 buf=" + new String(buf) + ",ret=" + ret);
		
		buf[0] = 'E';
		ret = jna.rf_select3(99, buf);
		System.out.println("99 buf=" + new String(buf) + ",ret=" + ret);
	}

}

console.out:

buf=auper man , ret=12
77 buf=auper man ,ret=12

the screen capter:

why rf_select1 and rf_select2 is right but rf_select3 is error ??

the differences is just the paramters order??

in the rf_select3 _Size is null

buf[0] = 'E';
ret = jna.rf_select3(99, buf);

2010-09-15 00:13 add info:

I found it's work good when HelloJna.java change rf_select3(long dev, byte[] abd) to rf_select3(NativeLong dev, byte[] abd)

public interface HelloJna extends Library {
	HelloJna instance = (HelloJna) Native.loadLibrary("hellojna", HelloJna.class);
	int rf_select1(byte[] abd);
	int rf_select2(byte[] abd, long dev);
	int rf_select3(NativeLong dev, byte[] abd);
}