From `malloc(3)`: Nonportable behavior The behavior of these functions when the requested size is zero is glibc specific; other implementations may

From `malloc(3)`: Nonportable behavior The behavior of these functions when the requested size is zero is glibc specific; other implementations may return NULL without setting errno, and portable POSIX programs should tolerate such behavior. See realloc(3p). POSIX requires memory allocators to set errno upon failure. However, the C standard does not require this, and applications portable to non-POSIX platforms should not assume this.