如何初始化或更改类中数组内的值？

Question

I am working with a class which has an array of characters.

class board
{
   char spot[64];

public:
   board();
   ~board(void);


};

I want to set each of the values in the array to the same character when the program begins how can I initialize there values in the constructor? and is there an easy way to access and allow changes to them by their index?

Thank you,

Answer 1

You cannot do this in C++03. However, it is possible to initialize arrays in a constructor initializer list in C++11:

board::board()
: spot { 1, 2, 1, 2, /* ... */ }
{  }

You can either type out the values, or come up with a magic variadic template to provide "N repeated values" (as long as the type is integral). Also, any missing elements are zero-initialized (eg char spot[4] { 1, 2 }; ).

For access, you use spot[i] inside the class, and you can write suitable accessor functions if you need to (though you should always worry if your class is just "forwarding" a member -- really you want your class to encapsulate some higher-order functionality).

If you want to see template code to "initialize an array of N with fixed values", perhaps you should post that as a separate question.

---

Update: Here is a naive template trick that initializes all array elements to the value 2 .

#include <iostream>
#include <utility>
#include <prettyprint.hpp>

class Foo
{
    int arr[10];

    template <typename T, T> struct Filler { };
    template <typename T, bool, unsigned int, T...> struct FillHelper { };

    template <typename T, unsigned int I, T V, T ...Vals>
    Foo(FillHelper<T, true, I, V, Vals...>)
    : arr { V, Vals... } { }

    template <typename T, unsigned int I, T V, T ...Vals>
    Foo(FillHelper<T, false, I, V, Vals...>)
    : Foo(FillHelper<T, I == 1, I - 1, V, V, Vals...>()) { }

    template <typename T, unsigned int N, T V>
    Foo(Filler<T, V>, T const (&)[N])
    : Foo(FillHelper<T, N == 1, N - 1, V>())
    { }

public:
    Foo() : Foo(Filler<int, 2>(), arr)
    {
        std::cout << "Foo: " << arr << "\n";
    }
};


int main()
{
    Foo x;
}

Output: Foo: [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

Answer 2

to set all the values in an array to a default value x, you can use something like std::fill_n

for example to set all the elements to -1
std::fill_n(array, 100, -1);

Answer 3

set each of the values in the array to the same character

Why not using memset ? For example init each of the values to 0x01

board::board()
{
    memset(spot, 0x01, sizeof(spot));
}

Answer 4

您只能使用for循环分配每个元素。