Question

I am using an aggregate initializer to set up a block of static data for a unit test.

I would like to use the array size as the expected number of elements, but this can fail if too few initializers are provided:

my_struct_type expected[14] =
{
    { 1.234, 0, 'c' },
    { 3.141, 1, 'z' },
    { 2.718, 0, 'a' }
};

This gives no compiler error in Visual Studio 2008.

I would like to be able to use it as such:

const unsigned expected_size = sizeof(expected) / sizeof(my_struct_type);

BOOST_CHECK_EQUAL(points.size(), expected_size);

for( int i = 0; i < expected_size; i++ )
{
    BOOST_CHECK_EQUAL(points[i].value, expected[i].value);
    BOOST_CHECK_EQUAL(points[i].count, expected[i].count);
    BOOST_CHECK_EQUAL(points[i].sym,   expected[i].sym);
}

but because I don’t have a compile-time guarantee of 14 points, this runs off the end of the array end of the provided values and into the default-initialized values.

Can I somehow enforce the number of aggregate array initializers at compile-time?

Answer 1

First: There might be a warning for this. Have you tried compiling at the highest warning level?

Then: If you swap which value is calculated and which is literal, you could raise a compile-time error:

my_struct_type my_array[] = // <== note the empty []
{
    { 1.234, 0, 'c' },
    { 3.141, 1, 'z' },
    { 2.718, 0, 'a' }
};

BOOST_STATIC_ASSERT( sizeof(my_array)/sizeof(my_array[0]) == 14 );