How to Initialize Member Arrays with Initializer Lists in C 0x?

Initializing Member Arrays with Initializer Lists

In C 0x, you may encounter the error "incompatible types in assignment" when attempting to initialize a member array with an initializer list.

To resolve this, consider using a variadic template constructor instead:

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

int main() {
    // Usage
    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
    foo f5(3.14);  // Error: narrowing conversion not allowed
    foo f6("foo"); // Error: no conversion from const char* to int
}</code>

If preserving the 'const' status is not essential, you could alternatively employ a function to load the array values:

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

However, this approach relinquishes compile-time bounds checking.

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