CODEWITHSUNDEEP
c++templates
Firat Akandere
Firat Akandere

Reputation: 523

2 constants in one parameter

I'm learning C++ from "C++ for Programmers" book. In "templates" section, there is a code like that:

template<typename T>
void printArray(const T * const array, int size)
{
    for (int i = 0; i < size; i++)
    {
        cout << array[i] << " ";
    }

    cout << endl;
}

My question is, the constants of first parameter in function. I have never seen two constants in one parameter. I tried to realize but I could not. Thanks for helps.

Upvotes: 1

Views: 112

Answers (3)

Shoe
Shoe

Reputation: 76240

const T * const means: a constant pointer to a constant T. Which means that both the pointer and the T pointed are constant.

A good rule for reading this kind of parameters is to read it right to left.

Upvotes: 4

derekerdmann
derekerdmann

Reputation: 18252

In your example, you have a const pointer to a const object of type T. This means you can't change where the pointer is pointing or the object to which it points.

You can actually have const in even more places in a single line. Take this declaration for example:

class MyClass {
public:
    const std::string& get_name(const int * const id) const;
};

In this case, the function get_name is constant, and can't modify the instance of MyClass. It takes in a constant pointer to a constant integer, and returns a constant reference to a string.

If you'd like to learn more about best practices while using const (and other parts of C++), I highly recommend Bruce Eckel's book Effective C++: 55 Specific Ways to Improve Your Programs and Designs.

Upvotes: 1

shuttle87
shuttle87

Reputation: 15934

The syntax just tells you that there is a pointer that is const and the thing it points to is also const.

For more reading I would recommend you have a look at:

http://www.parashift.com/c++-faq/const-ptr-vs-ptr-const.html

http://www.parashift.com/c++-faq/const-correctness.html

Upvotes: 0

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