It always boggles me why people went with null-terminated strings in C instead of just putting the length of the string in the first 4 bytes and then the string after that.

And just generally doing that for all arrays. That way if you're passed ONLY a pointer to the array, you can always tell how long it is without requiring the caller to tell you how long it is, which seems to be a common theme among C functions. And that also allows your string to contain null characters, which is useful in many circumstances.