how to dereference a pointer of a map of pointers to objects in c++

» cpp » how to dereference a pointer of a map of pointers to objects in c++

By : Henry Stukenborg

Date : November 18 2020, 04:01 AM

this one helps. I am just reviewing.

code :

... (*_employeePayroll)["Karl"]->employeeID ...

...
itEmployeeID = _employeePayroll->find("Karl");
if ( itEmployeeID != _employeePayroll->end() )
{
    ... (itEmployeeID->second)->employeeID ...

#include    <iostream>
#include    <string>
#include    <map>

class Employee
{
public:
    int     employeeID;

    Employee()
    {
        employeeID = 123;
    }
};

int main(int argc, char* argv[]) {
    std::map<std::string, Employee *>                   *_employeePayroll;
    std::map<std::string, Employee *>                   _employeeID;
    std::map<std::string, Employee *>::const_iterator   itEmployeeID;

    _employeePayroll = &_employeeID;
    (*_employeePayroll)["Karl"] = new Employee;

    itEmployeeID = _employeePayroll->find("Karl");
    if ( itEmployeeID != _employeePayroll->end() )
    {
        std::cout << (itEmployeeID->second)->employeeID;
        std::cout << std::endl;
    }

    return 0;
}

#include    <iostream>
#include    <string>
#include    <map>

class Employee
{
public:
    int     employeeID;

    Employee()
    {
        employeeID = 123;
    }
};

int main(int argc, char* argv[]) {
    std::map<std::string, Employee *> *_employeePayroll;
    std::map<std::string, Employee *> _employeeID;
    _employeePayroll = &_employeeID;

    int iValue;

    (*_employeePayroll)["Karl"] = new Employee;
    iValue = (*_employeePayroll)["Karl"]->employeeID;
    std::cout << iValue;
    std::cout << std::endl;

    return 0;
}

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Dereference of null pointer, but I am not using pointers

By : Iqra Farheen

Date : March 29 2020, 07:55 AM

will be helpful for those in need The first if statement in your init method is checking whether or not [super init] returns nil. (Technically it should be written if ((self = [super init])), which the new LLVM compiler will warn you about).
The static analyser is checking ALL possible code paths, even the case where [super init] returns nil. In this case, your if statement fails and self is nil. If self is nil then its instance variables aren't accessible.

I could not figure out how to dereference this pointer for a sizeof() and void pointers

By : ProphecyX

Date : March 29 2020, 07:55 AM

this will help sizeof is compile-time constant that works on exact type you provide. sizeof of void* is just a size of pointer on your machine (likely 4/8 bytes). Just store size along with other data.

Segmentation fault trying to dereference a pointer from a vector of pointers

By : user3605960

Date : March 29 2020, 07:55 AM

I wish this helpful for you In my opinion the vector elements are badly initialized. Perhaps you have to test the code that fill the vector independently before testing to extract them. Sorry for my english ;)

Pointers: Read access violation when trying to dereference pointer by adding a large number

By : Lee Dallas

Date : March 29 2020, 07:55 AM

wish of those help arth is pointing to a single instance of an int. Adding any non-zero value to arth and subsequently dereferencing that new pointer value reads a memory location outside the bounds of the original int. This invokes undefined behavior.
With undefined behavior, anything can happen. Your program may crash, it may output strange results, or it may appear to work properly. The fact that you didn't crash on the *(arth + 1)) case but did crash on the *(arth + 1000)) is an example of that.

How to overload the arrow dereference operator->() not for solid objects but for pointers

By : Hendrik Witarsa

Date : March 29 2020, 07:55 AM

I wish did fix the issue. You cannot replace -> on a pointer.
You can create a smart pointer1 that overloads ->, but built-in operators may not be overloaded.

code :

auto m = DatabaseManager::instance();
m->Query(...); // db->Query

class DatabaseManager {
  struct DatabaseManagerPtr {
    DatabaseManager* ptr;
    sqdb::Db * operator->() {
      return ptr?ptr->db:nullptr;
    }
  };
  friend struct DatabaseManagerPtr;
private:
  static DatabaseManager * sharedInstance_;
  sqdb::Db *db = nullptr;

public:
  static DatabaseManagerPtr instance() {
    return {sharedInstance_};
  }
};