Question

I’m working on some embedded software where there is some static information about “products”. Since the information for a certain product never changes during execution I would like to initialize these data structures at compile time to save some space on the stack/heap.

I made a Product class for the data, intending to make a huge array of all the products in the system and then do lookups in this structure, but I haven’t figured out quite how to get it working. The arrays are giving me loads of trouble. Some psuedo code:

class Product {
    int m_price;
    int m_availability[]; // invalid, need to set a size
    ... etc

    // Constructor grabbing values for all members
    Product(int p, int a[], ...);
}

static const Product products[] = 
{
    Product(99, {52,30,63, 49}, ...), // invalid syntax
    ...                    
}                     

Is there a way to making something like this work? The only thing I can think of would be to organize by attribute and skip the whole Product object. I feel that would make the whole thing harder to understand and maintain though.

Does anyone have any suggestions on how I might best organize this kind of data?

Thank you.

Answer 1

An old school C style static array of structs sounds like a perfect match to your requirements. Initializes at compile time, zero runtime overhead, no use of stack or heap. It’s not a co-incidence that C is still a major player in the embedded world.

So (one recipe – plenty of scope to change the details of this);

// in .h file
    class Product {
    public: // putting this first means the class is really a struct
        int m_price;
        int m_availability[4]; 
        //.... (more)
    };
    extern const Product product_array[];
    extern const int     product_array_nbr;

// in .cpp file
    const Product product_array[] =
    {
        {
             23,
             {56,1,2,4},
             //....(more)
        },
        {
             24,
             {65,1,2,4},
             //....(more)
        },
        //....(more)
    };

    const int product_array_nbr = sizeof(product_array)/sizeof(product_array[0]);