Changing values in polymorphic boost::shared_ptr (inside std::vector) - c++

Question

I have the following base calibration struct:
struct Standard
{
public:
unsigned long ulCamID;
std::string sCalibrationModel;
float fC;
float fXh;
float fYh;
Standard()
{
ulCamID = 0;
fC = fXh = fYh = 0.0;
}
virtual ~Standard()
{
}
};
And derived structs such as:
struct Aus: public Standard
{
public:
float fK1;
float fK2;
float fK3;
float fP1;
float fP2;
float fB1;
float fB2;
Aus()
{
fC = fXh = fYh = fK1 = fK2 = fK3 = fP1 = fP2 = fB1 = fB2 = 0.0;
}
};
Because I do not know at compile how many Calibrations I will need, nor which calibration models, I thought it convenient to put it into a std::vector and use boost::shared_ptr to point to them. I do this like so:
typedef boost::shared_ptr<CalibrationModels::Standard> shr_ptr;
std::vector<shr_ptr> vec;
shr_ptr p(new CalibrationModels::Aus);
vec.push_back(p);
p.reset(new CalibrationModels::Brown);
vec.push_back(p);
This seems to work fine (the debugger reports that the pointers inside the vector point to the derived struct). However, I have difficulties now to access/change the values inside the vector. If I try something like this:
boost::dynamic_pointer_cast<CalibrationModels::Aus>(vec.at(0)).px->fK3 = 1.3221e-9
It tells me that px is private ( ‘boost::shared_ptr::element_type* boost::shared_ptr::px’ is private element_type * px; ).
What is the proper way to access and manipulate the values inside those pointers to derived structs?

Answer 1

The problem you have is that px is a private member of the smart pointer. To access your class boost provides the -> operator. You can use that to access the pointer as you would use it for a regular pointer. This would change your line to this:
boost::dynamic_pointer_cast<CalibrationModels::Aus>(vec.at(0))->fK3 = 1.3221e-9;
^^ Difference here
Note that, if you actually need the value, you can use the get() method to get the pointer that is stored in the shared_ptr.