JNI字符集的轉換

    寫Java JNI的時候最頭痛的莫過於字符集的轉換問題，衆所周知，Java裏字符串是以Unicode編碼存儲的，而C/C++裏大部分是單字節處理，這就涉及到一個轉換的問題，下面是兩個函數用來在JString到Char*之間的轉換：

//author Naven 2003 for both Win32 and Unix os

//爲了便於使用，無需另連接庫，Win32裏需自己寫雙字節memset函數
#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

//將Java裏jstring類型轉換成單字節字符串
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; 
}

//將單字節字符串轉換成Java裏可使用的jstring類型
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;
}