JNI字符集的转换

写Java JNI的时候最头痛的莫过于字符集的转换问题，众所周知，Java里字符串是以Unicode编码存储的，而C/C++里大部分是单字节处理，这就涉及到一个转换的问题，下面是两个函数用来在JString到Char*之间的转换：

//author Naven 2003 for both Win32 and Unix os

//为了便于使用，无需另连接库，Win32里需自己写双字节memset函数
#if    defined(_WIN32)  defined(__WIN32__)
wchar_t *mywmemset(wchar_t *_S, wchar_t _C, size_t _N)
{
    wchar_t *_Su = _S;
    for (; 0 < _N; ++_Su, --_N)
            *_Su = _C;
    return (_S);
}
#endif

//将Java里jstring类型转换成单字节字符串
size_t JStringToChars(JNIEnv *env,
    const jstring jstr, char *mbstr, const size_t mbslen)
{
    const jchar *jwstr;
    wchar_t *wbuf=0;
    size_t nsize=0;
    jsize jlen=0;
    register int i=0;

    memset(mbstr, 0, mbslen);
    if( jstr == NULL ) return 0;
    jwstr = (*env)->GetStringChars(env, jstr, 0);

    jlen = (*env)->GetStringLength(env, jstr);
    if( jlen <= 0 ) return 0;

#if    defined(_WIN32)  defined(__WIN32__)
    wbuf = (wchar_t *) jwstr;
    nsize = wcstombs(mbstr, wbuf, mbslen-1);
#else
    wbuf = (wchar_t *) malloc((jlen+1)*sizeof(wchar_t));
    mywmemset(wbuf, (wchar_t)0, (size_t)(jlen+1));

    for( i = 0; i < jlen; i ++ )
        wbuf[i] = (wchar_t)jwstr[i];

    nsize = wcstombs(mbstr, wbuf, mbslen-1);
    free(wbuf);
#endif

    if( nsize >= 0 && nsize < mbslen )
        mbstr[nsize] = 0;
   
    return nsize;
}

//将单字节字符串转换成Java里可使用的jstring类型
size_t CharsToJString(JNIEnv *env,
    const char *mbstr, jstring *jstr)
{
    jchar *jwstr=0;
    wchar_t *wcstr=0;
    size_t slen=0, nsize=0;
    register int i=0;

    if( mbstr != NULL )
        slen = strlen(mbstr);
    if( mbstr == NULL  slen <= 0 ) {
        *jstr = (*env)->NewStringUTF(env, "");
        return 0;
    }

    wcstr = (wchar_t *) malloc((slen+1)*sizeof(wchar_t));
    mywmemset(wcstr, 0, slen+1);
    nsize = mbstowcs(wcstr, mbstr, slen*2);
   
    jwstr = (jchar *) wcstr;

#if    defined(_WIN32)  defined(__WIN32__)
#else
    for(i =0; i < (int)nsize; i ++) {
        jwstr[i] = jwstr[i*2];
    }
    jwstr[nsize] = 0;
#endif

    if( nsize <= 0 )
        *jstr = (*env)->NewStringUTF(env, "");
    else
        *jstr = (*env)->NewString(env, jwstr, nsize);

    free(wcstr);
    return nsize;
}