I'm not sure when this array initialization was standardized but since I learned C almost 20 years ago I haven't been treated to any compiler that didn't understand it.

You've got a point about the strlen. Actually I had it in a separate function first that got a const char* string argument, in that case any optimizer worth its name should notice it's an invariant and do the caching transparently. I haven't looked at the compiled code so it may be that a non-const string would disable this optimization, although the code is simple enough that I'd think the optimizer would notice the string is never modified inside the loop and do it anyway.