C++ double free or corruption (out) - c++

Question

Here is my code:
#include "Accounts.h"
using namespace Vibranium;
void Accounts::LoadTable(RowResult &res) {
std::vector<AccountsStruct> accounts;
AccountsStruct accountsStruct;
for (Row row : res.fetchAll()){
accountsStruct.id = row[0].get<int>();
accountsStruct.email = row[1].get<std::string>();
accountsStruct.warTag = row[2].get<std::string>();
accountsStruct.state = row[4].get<int>();
accountsStruct.name = row[5].get<std::string>();
accountsStruct.lastname = row[6].get<std::string>();
accountsStruct.country = row[7].get<std::string>();
accountsStruct.dob_month = row[8].get<int>();
accountsStruct.dob_day = row[9].get<int>();
accountsStruct.dob_year = row[10].get<int>();
accountsStruct.balance = row[11].get<double>();
accountsStruct.created_at = row[12].get<std::string>();
accountsStruct.updated_at = row[13].get<std::string>();
accountsStruct.account_role = row[15].get<int>();
accountsStruct.rank = row[16].get<int>();
accountsStruct.playerRole = row[17].get<int>();
Data.emplace_back(&accountsStruct);
}
std::cout << "SIZE: " << Data.size() << std::endl;
}
Data is std::vector<std::unique_ptr<DataStruct>> Data;.
To add into the vector I call Data.emplace_back(&accountsStruct); which leads me to the following output:
SIZE: 2
double free or corruption (out)
Process finished with exit code 134 (interrupted by signal 6: SIGABRT)
I am sure this line Data.emplace_back(&accountsStruct); is causing the issue. Why? How can I fix it?

Answer 1

You're trying to free memory not allocated with new (stack memory, to be precise).
std::vector<std::unique_ptr<DataStruct>> Data;
AccountsStruct accountsStruct; // <-- a stack variable
Data.emplace_back(&accountsStruct); // <-- an instance of unique_ptr is created using the address of accountsStruct
So when Data is destroyed, unique_ptr calls delete on that pointer (not good!!).
I can think of 2 possible solutions:
Allocate accountsStruct on the heap using std::make_unique:
for (auto& row : res.fetchAll()) {
Data.emplace_back(std::make_unique<AccountsStruct>()); // allocate a new instance on the heap
AccountsStruct& accountsStruct = *Data.back(); // get a reference to that instance
accountsStruct.id = row[0].get<int>(); // fill it normally ...
accountsStruct.email = row[1].get<std::string>();
accountsStruct.warTag = row[2].get<std::string>();
. . .
Simplify Data to store by-value: std::vector<DataStruct> Data;
for (auto& row : res.fetchAll()) {
Data.emplace_back(); // allocates a new instance of AccountsStruct in-place
AccountsStruct& accountsStruct = Data.back(); // get a reference to that instance
accountsStruct.id = row[0].get<int>(); // fill it normally ...
accountsStruct.email = row[1].get<std::string>();
accountsStruct.warTag = row[2].get<std::string>();
. . .

Answer 2

Data should contain a std::unique_ptr<AccountsStruct>. I'm afraid, unique_ptr can't be created from AccountsStruct.
So, create struct dynamically, fills by data, create unique_ptr from pointer and add it to vector.

Answer 3

The problem in your code is that you provide an address of a local variable to the constructor of std::unique_ptr.
I assume that Data is std::vector<std::unique_ptr<AccountsStruct>> If AccountsStruct has constructor with no arguments, you can try this:
#include "Accounts.h"
using namespace Vibranium;
void Accounts::LoadTable(RowResult &res) {
std::vector<AccountsStruct> accounts;
// create an instance in the vector and get a reference to it
// auto will be std::unique_ptr<AccountsStruct>&;
auto &accountsStruct = Data.emplace_back();
// work with that reference
for (Row row : res.fetchAll()){
accountsStruct->id = row[0].get<int>();
accountsStruct->email = row[1].get<std::string>();
accountsStruct->warTag = row[2].get<std::string>();
accountsStruct->state = row[4].get<int>();
accountsStruct->name = row[5].get<std::string>();
accountsStruct->lastname = row[6].get<std::string>();
accountsStruct->country = row[7].get<std::string>();
accountsStruct->dob_month = row[8].get<int>();
accountsStruct->dob_day = row[9].get<int>();
accountsStruct->dob_year = row[10].get<int>();
accountsStruct->balance = row[11].get<double>();
accountsStruct->created_at = row[12].get<std::string>();
accountsStruct->updated_at = row[13].get<std::string>();
accountsStruct->account_role = row[15].get<int>();
accountsStruct->rank = row[16].get<int>();
accountsStruct->playerRole = row[17].get<int>();
}
std::cout << "SIZE: " << Data.size() << std::endl;
}
If AccountsStruct is derived from DataStruct you can use:
data.emplace_back(std::make_unique<AccountData>());