string和wstring相互转换方法，这个是对以前的修改，主要修改了输入为空，导致的小bug。

/*
	string 转换为 wstring 
*/
std::wstring c2w(const char *pc)
{
	std::wstring val = L"";

	if(NULL == pc)
	{
		return val;
	}
	//size_t size_of_ch = strlen(pc)*sizeof(char);
	//size_t size_of_wc = get_wchar_size(pc);
	size_t size_of_wc;
	size_t destlen = mbstowcs(0,pc,0);
	if (destlen ==(size_t)(-1))
	{
		return val;
	}
	size_of_wc = destlen+1;
	wchar_t * pw  = new wchar_t[size_of_wc];
	mbstowcs(pw,pc,size_of_wc);
	val = pw;
	delete pw;
	return val;
}
/*
	wstring 转换为 string
*/
std::string w2c(const wchar_t * pw)
{
	std::string val = "";
	if(!pw)
	{
   		return val;
	}
	size_t size= wcslen(pw)*sizeof(wchar_t);
	char *pc = NULL;
	if(!(pc = (char*)malloc(size)))
	{
   		return val;
	}
	size_t destlen = wcstombs(pc,pw,size);
	/*转换不为空时，返回值为-1。如果为空，返回值0*/
	if (destlen ==(size_t)(0))
	{
		return val;
	}
	val = pc;
	delete pc;
	return val;
}