coco2d-x中编码问题。GBK转UTF-8

int GBKToUTF8(std::string & gbkStr, const char* toCode, const char* fromCode)
{

iconv_t iconvH;
iconvH = iconv_open(fromCode, toCode);
if (iconvH == 0)
{
return -1;
}

const char* strChar = gbkStr.c_str();
const char** pin = &strChar;
size_t strLength = gbkStr.length();
char* outbuf = (char*) malloc(strLength*4);
char* pBuff = outbuf;

memset( outbuf, 0, strLength*4);
size_t outLength = strLength*4;
if (-1 == iconv(iconvH, pin, &strLength, &outbuf, &outLength))
{
iconv_close(iconvH);
return -1;
}
gbkStr = pBuff;
iconv_close(iconvH);
return 0;
}