How to Initialize a C Member Array with an Initializer List?

Assignment Error When Initializing C 0x Member Array with Initializer_list

While attempting to initialize a member array with an initializer list, you encounter a compiler error: incompatible types in assignment of ‘std::initializer_list’ to ‘const int [2]’.

Solution Using Variadic Template Constructor

Rather than an initializer list constructor, you can opt for a variadic template constructor:

<code class="cpp">struct Foo {
    int x[2];
    template <typename... Ts>
    Foo(Ts... ts) : x{ts...} {}
};</code>

With this approach, you can initialize your Foo object as follows:

<code class="cpp">Foo f1(1, 2);     // OK
Foo f2{1, 2};     // Also OK
Foo f3(42);      // OK; x[1] zero-initialized
Foo f4(1, 2, 3); // Error: too many initializers</code>

Solution Using Non-Constant Member Array and Initialization in Function Body

If constantness is not essential, you can initialize the array within the function body after skipping initialization in the constructor:

<code class="cpp">struct Foo {
    int x[2]; // or std::array<int, 2> x;
    Foo(std::initializer_list<int> il) {
       std::copy(il.begin(), il.end(), x);
       // or std::copy(il.begin(), il.end(), x.begin());
       // or x.fill(il.begin());
    }
}</code>

This method, however, lacks the compile-time bounds checking offered by the variadic template constructor.

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