Re: How to make the vector size unchanged but values not?
shuisheng wrote:
Dear All,
I have a question. Assume
#include <vector>
using namespace std;
class A
{
private:
vector<int> v;
int n;
public:
void Reset(int i)
{
n = i;
v.resize(i);
}
vector<int>& Vector()
{
return v;
}
};
For class A, 'n' and the size of 'v' must be always consistent. Every
time n is changed, v is reset with the size n. If n is not changed,
the vector v's size can not change, but its values can change, such as
A::Vector()[2] = 3;
But user can use A::Vector().resize() to change the size of the
vector. How can I avoid it and still keep all the std::vector 's
functions to change the values?
The easy way is to ditch the variable i. Since it cannot be observed from
the outside, it does not make any sense to carry it around. Probably this
possibility is due to oversimplification of the problem and does not arise
in the original setting.
The standard way would be to not expose the internal vector by means of a
Vector() method but to narrow down its interface and make the needed
functions available through forwarding. They would also update i.
The hard way would be to not return a reference in the Vector() method, but
a smart reference that updates i upon destruction. Since we cannot overload
the dot-operator, there are some limitations to this method. We can,
however, return a smart pointer.
All in all, you seem to have a design problem that is best solved by
avoiding the problem. What is the underlying conundrum that you are
struggling with?
Best
Kai-Uwe Bux
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