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Topic: jni小错误

1.jni小错误

Posted by: manhunt
Posted on: 2006-04-23 11:07

照着"Java进阶-JNI使用技巧点滴（二）"中的例子编了个很小的程序，就是在java中定义一个字符串利用c显示出来。

其中一个c.cpp 用到自定义函数convertUniToANSI，用cl命令编译成dll文件时出现以下错误：

c.cpp ( 8 ) : error c2065: 'convertUniToANSI' : undeclared identifier
c.cpp ( 20 ) : error c2373: 'convertUniToANSI': redefinition; defferent type modifiers
=====================================
以下为代码：

c语言主程序c.cpp

#include <stdio.h>
#include "connection.h"
#include "windows.h"

JNIEXPORT void JNICALL Java_connection_HelloWorld (JNIEnv*env, jclass jobject,jstring text)
{
char* sp;
convertUniToANSI(env,text,sp);
printf("sp= %s\n",sp);
}
JNIEXPORT jstring JNICALL Java_connection_cToJava (JNIEnv *env,jclass obj)
{
jstring jstr;
char str[]="fuck this world!\n";
jstr=env->NewStringUTF(str);
return jstr;
}

void convertUniToANSI(JNIEnv *env,jstring oldStr,char* newStr)
{
int desc_len=256*2;
int len;
if(oldStr==NULL||newStr==NULL)
return ;
wchar_t *w_buffer = new wchar_t[256];
wcscpy(w_buffer,env->GetStringChars(oldStr,0));
env->ReleaseStringChars(oldStr,w_buffer);
len = WideCharToMultiByte(CP_ACP,0,w_buffer,1024,newStr,desc_len,NULL,NULL);
if(len>0 && len<desc_len)
{
newStr[len]='\0';
}
delete[] w_buffer;
}
=====================================
连接程序:connection.java

public class connection
{
static
{
System.loadLibrary( "c" );
}
public native static void HelloWorld(String text);
//public native static String cToJava();
}
====================================
测试程序:test.java

public class test
{
public static void main(String[] args)
{
connection b=new connection();
String text="fthe world!";
b.HelloWorld(text);
//System.out.println(b.cToJava());
}
}

test.rar (1.31k)

2.Re:jni小错误 [Re: manhunt]	Copy to clipboard
Posted by: damondeng Posted on: 2006-05-10 12:58 你把方法写在调用后面了... 在CPP里, 必须先写方法, 再写调用, 如果一定在要方法实现前调用, 需要在调用前声名一下. 写JNI和JVMPI, JVMTI等和C/C++相关的要注意培养C/C++的调试能力. 我没拿程序来编译(机器刚当了,没安装), 从程序看应该是这个问题

3.Re:jni小错误 [Re: manhunt]	Copy to clipboard
Posted by: ranchgirl Posted on: 2006-05-17 14:07 Here is an excellent JNI course notes with exercises and complete solutions. Take a look! Programmming in C/C++ with the Java Native Interface