CODEWITHSUNDEEP
c++c++14shared-ptrstdmap
whoami
whoami

Reputation: 1899

shared_ptr to map populated in a method comes back empty in the caller

I am initializing a shared_ptr to map in a separate function called GetData. This map is passed as argument to GetData function. However, in the main, map comes back empty after the call to GetData function.

#include <memory>
#include <map>

void  GetData(std::shared_ptr<std::map<int, int>> data);

int main()
{
    std::shared_ptr<std::map<int, int>> data2 = std::make_shared<std::map<int, int>>();
    GetData(data2);
    return 0;
}

void GetData(std::shared_ptr<std::map<int, int>> data)
{

    data = std::make_shared<std::map<int, int>>
        (std::initializer_list<std::map<int, int>::value_type>{
            { 1, 2 },
            { 5, 6 },
            { 4, 5 }
    });
}

What am I doing wrong here?

UPDATE: If I re-write method as follows while parameter still not passed by reference, I do get map populated in the main after call to GetData method. 

void GetData(std::shared_ptr<std::map<int, int>> data)
{
    data->insert(std::pair<int, int>(1,2));
    data->insert(std::pair<int, int>(45, 2));
}

Upvotes: 0

Views: 3220

Answers (1)

selbie
selbie

Reputation: 104514

Pass data by reference:

void GetData(std::shared_ptr<std::map<int, int>>& data)

Or preferably, so it makes more sense as function that "gets" and returns something, have the value returned

std::shared_ptr<std::map<int, int>> GetData()
{

    return std::make_shared<std::map<int, int>>
        (std::initializer_list<std::map<int, int>::value_type>{
            { 1, 2 },
            { 5, 6 },
            { 4, 5 }
    });

}

Upvotes: 5

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