Checked-size array parameters in C

GCC also has an extension to support references to other parameters of the function:

    #include <stddef.h>
    void foo(size_t n, int b[static n]);

It is not limited to compile-time constants. Doesn't work in clang, sadly.

Pointer to array is not only type-safe, it is also objectively correct and should have always been the syntax used when passing in the address of a known, fixed size array. This is all a artifact of C automatically decaying arrays to pointers in argument lists when a array argument should have always meant passing a array by value; then this syntax would have been the only way to pass in the address of a array and we would not have these warts. Automatic decaying is truly one of the worst actual design mistakes of the language (i.e. a error even when it was designed, not the failure to adopt new innovations).

Funny thing about that n[static M] array checking syntax–it was even considered bad in 1999, when it was included:

"There was a unanimous vote that the feature is ugly, and a good consensus that its incorporation into the standard at the 11th hour was an unfortunate decision." - Raymond Mak (Canada C Working Group), https://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_205.htm

Better option: just wrap it in a unique struct.

There are perhaps only 3 numbers: 0, 1, and lots. A fair argument might be made that 2 also exists, but for anything higher, you need to think about your abstraction.