Question

I’m working on a GUI framework, where I want all the elements to be identified by ascii strings of up to 8 characters (or 7 would be ok).

Every time an event is triggered (some are just clicks, but some are continuous), the framework would callback to the client code with the id and its value.

I could use actual strings and strcmp(), but I want this to be really fast (for mobile devices), so I was thinking to use char constants (e.g. int id = ‘BTN1’;) so you’d be doing a single int comparison to test for the id. However, 4 chars isn’t readable enough.

I tried an experiment, something like-
long int id = L’abcdefg’;

… but it looks as if char constants can only hold 4 characters, and the only thing making a long int char constant gives you is the ability for your 4 characters to be twice as wide, not have twice the amount of characters. Am I missing something here?

I want to make it easy for the person writing the client code. The gui is stored in xml, so the id’s are loaded in from strings, but there would be constants written in the client code to compare these against.

So, the long and the short of it is, I’m looking for a cross-platform way to do quick 7-8 character comparison, any ideas?

Answer 1

Are you sure this is not premature optimisation? Have you profiled another GUI framework that is slow purely from string comparisons? Why are you so sure string comparisons will be too slow? Surely you’re not doing that many string compares. Also, consider strcmp should have a near optimal implementation, possibly written in assembly tailored for the CPU you’re compiling for.

Anyway, other frameworks just use named integers, for example:

static const int MY_BUTTON_ID = 1;

You could consider that instead, avoiding the string issue completely. Alternatively, you could simply write a helper function to convert a const char[9] in to a 64-bit integer. This should accept a null-terminated string “like so” up to 8 characters (assuming you intend to throw away the null character). Then your program is passing around 64-bit integers, but the programmer is dealing with strings.

Edit: here’s a quick function that turns a string in to a number:

__int64 makeid(const char* str)
{
    __int64 ret = 0;
    strncpy((char*)&ret, str, sizeof(__int64));
    return ret;
}