C++ Shared_Ptr 不共享？

Question

I'm a complete novice to smart pointers, much less C++, so bear with me here. My program attempts to construct classes with unique serial numbers. It does this by placing already-made serial numbers into a shared_ptr. In theory, this pointer should share the set to all of the classes, but it fails to. This is my class code:

#include <iostream>
#include <cstdlib>
#include <set>
#include <memory>
#include <algorithm>

struct numbered{
    numbered();
    int mysn;
    std::shared_ptr<std::set<int>> catalogue = std::make_shared<std::set<int>> ();
};

numbered::numbered(){
    while (true){
        int check = rand() & 100; 
        if(catalogue->find(check) == catalogue->end()){  // if this number is not already in the catalogue
            mysn = check; // make this the serial number
            // add this to the log of illegal serial numbers
            catalogue->insert(mysn);
            return; // stop making new numbers to check for            
        }
        else{ // temporary provision, just to get this to work
            mysn = 5;
            return;
        }
    }
}

This is my main code:

#include <iostream>
#include "numberedheader.hpp"

using namespace std;

int main(){
    numbered a, b;
    cout << a.mysn << " " << b.mysn << endl;
    system("pause");
    return 0;
}

I've ran some tests. Catalogue is able to find ints and is able to update to include the newest ints, however, there seems to be a new catalogue set for every class rather than one shared one. What am I doing wrong here? Thank you for your time.

Answer 1

You seem to misunderstand the concept of shared pointers . They share ownership , not memory . Smart Pointers are all about ownership.

With a shared pointer, the memory it owns is kept alive as long as there are objects referencing it
( different with a unique pointer where only one can own this memory. if this single reference is destroyed, the memory owned by a unique ptr is destroyed automatically.)

You barely need a shared pointer in real life. If you want to share the content across instances, you need to make it static.