c++ 里面的字符类型转换

char ch[1024] = "xxxx";
int num = MultiByteToWideChar(0,0,ch,-1,NULL,0);
wchar_t *wide = new wchar_t[num];
MultiByteToWideChar(0,0,ch,-1,wide,num);

wchar_t widestr[1024] = L"xxxx";
int num = WideCharToMultiByte(CP_OEMCP,NULL,widestr,-1,NULL,0,NULL,FALSE);
char *pchar = new char[num];
WideCharToMultiByte (CP_OEMCP,NULL,widestr,-1,pchar,num,NULL,FALSE);