c# 클라 c++서버 패킷 전송 문의

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public class PackHead
{
    private int PacketSize;
    public LoginPacket Type;
 
    public PackHead()
    {
        Type = LoginPacket.NONE;
        PacketSize = 0;
    }
 
    public PackHead(LoginPacket _Type, int _PacketSize)
    {
        Type = _Type;
        PacketSize = _PacketSize;
    }
}
 
[StructLayout(LayoutKind.Sequential, Pack = 1)]
public class Login_info : PackHead
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 15)]
    private string ID_value;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 15)]
    private string PW_value;
 
    public Login_info() { }
    public Login_info(string _ID, string _PW)
        : base(LoginPacket.LOGIN_req, Marshal.SizeOf(new Login_info()))
    {
        ID_value = _ID;
        PW_value = _PW;
    }
 
}

class PacketHeader
{
private:
	unsigned int PacketSize;
	LoginPacket Type;
 
public:
	PacketHeader() : Type(NONE), PacketSize(0) { }
 
	PacketHeader(LoginPacket _Type, unsigned int _PacketSize) : Type(_Type), PacketSize(_PacketSize) { }
 
	LoginPacket get_PacketHeader()
	{
		return Type;
	}
 
};
class Login_info : public PacketHeader
{
public:
	char ID_value[15];
	char PW_value[15];
 
public:
	Login_info() :ID_value(), PW_value(){}
	Login_info(std::string _ID, std::string _PW) :PacketHeader(LOGIN_req, sizeof(Login_info))
	{
		strcpy(ID_value, _ID.c_str());
		strcpy(PW_value, _PW.c_str());
	}
 
};

std::cout << (int)buf[0] << std::endl; // 전송받은 패킷 크기
std::cout << (int)buf[4] << std::endl; // enum값
std::cout << buf[7] << std::endl; // ID부분 출력 안됨(공백으로나옴)
std::cout << buf[22] << std::endl; // PW출력 안됨( 공백)