> Do you mean the C++ std::max_align_t? Does C99 have something like that?
> 
> The Linux malloc() manual page says:
> 
> "The malloc() and calloc() functions return a pointer to  the  allocated memory,  which  is  suitably  aligned for any built-in type."

C11 has max_align_t, but also for C99 "any builtin type" means 16 byte alignment
for long double on x64, so malloc() and calloc() are required to align 16 bytes
with -std=c99 (and earlier).

max_align_t is just a shorthand to express the concept.