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;
}