Using getsockopt to check the initial value of SO_DEBUG option - c++

Question

I am trying to understand the nature of getsockopt(int s, int level, int optname, void *optval, socklen_t *optlen).
I am trying to see the initial status of SO_DEBUG and I am referring to this link https://www.mkssoftware.com/docs/man3/getsockopt.3.asp , and I am not sure if I am doing this the correct way because I am getting random values.
//***********************************************Libraries****************************************************************
#include <iostream>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <errno.h>
using namespace std;
//************************************************************************************************************************
int main()
{
int * optval;
int optionDebug = 0;
socklen_t optlen;
int sockFD;
sockFD = socket(AF_INET, SOCK_STREAM ,0);
optlen =sizeof(optval);
int udpFD;
udpFD = socket(AF_INET, SOCK_DGRAM,0);
optionDebug = getsockopt(sockFD, SOL_SOCKET, SO_DEBUG, optval, &optlen) ;
cout<<"My value "<< *optval<<endl;
return 0;
}

Answer 1

To retrieve the value for optval you need to pass the address of a valid variable (not an uninitialized pointer):
ExpectedOptType optval;
// ^^^^^^^^^^^^^^^ Put whatever type (probably a enum) is expected for
// the specific option
optionDebug = getsockopt(sockFD, SOL_SOCKET, SO_DEBUG, &optval, &optlen);
// ^
Read more details about how it works here: getsockopt(2).