Somehow I understood the question to imply there's no compiler support for length-prefixed strings in C. The following example shows, at least you can start your own C string library, where string lengths are counted at compile time, with a construct like this:
#define PREFIX_STR(s) ((prefix_str_t){ sizeof(s)-1, (s) }) typedef struct { int n; char * p; } prefix_str_t; int main() { prefix_str_t string1, string2; string1 = PREFIX_STR("Hello!"); string2 = PREFIX_STR("Allows \0 chars (even if printf directly doesn't)"); printf("%d %s\n", string1.n, string1.p); /* prints: "6 Hello!" */ printf("%d %s\n", string2.n, string2.p); /* prints: "48 Allows " */ return 0; } This won't, however, come with no issues as you need to be careful when to specifically free that string pointer and when it is statically allocated (literal char array).
Edit: As a more direct answer to the question, my view is this was the way C could support both having string length available (as a compile time constant), should you need it, but still with no memory overhead if you want to use only pointers and zero termination.
Of course it seems like working with zero-terminated strings was the recommended practice, since the standard library in general doesn't take string lengths as arguments, and since extracting the length isn't as straightforward code as char * s = "abc", as my example shows.