创建类时如何定义数组的大小？

Question

I want to create an array contained inside of a class. The array will be of fixed size, but I don't know that fixed size until the constructor of the class.

Let's say the users create something like: Fibanocci f(value1, value2, size) . The size argument would then used to determine the number of elements in the containing array, which will be fixed throughout the entire life of the Fibanocci instance.

How do I pull this off?

Answer 1

Go with std::vector<type> vector instead and you can do int size = vector.size() . You can initialize the size of the vector in the constructor. For example,

// MyClass.hpp
class MyClass
{
public:
    MyClass();

    // Say I know this vector is going to have 5 elements
    std::vector<double> myVector; 
}

// MyClass.cpp
MyClass::MyClass() : myVector(5)
{
    int vectorSize = myVector.size(); //vectorSize = 5
}

Answer 2

This is not possible since C/C++ requires all classes to have constant sizeof . The only way around is to use heap allocation ( new or std::vector as @jlack proposed or whatever else)

Answer 3

Array size must be known at compile-time!! Don't think you will lose performance by using vector, it's a wrapper over array. If you are really stringent and have C++11, you can use array from the standard library.

Do I use resize or reserve?

Reserve will allocate memory but not insert anything. Resize will insert copies of default-constructed objects, unless you specify a parameter.

Answer 4

Java makes the array dynamic it will assign size at run time. Proxy class will form whose object is this array.

int a[]=new int[10];