Re: C and turtles, 80286 protected mode

On 16/10/2024 03:08, John Levine wrote:

According to MitchAlsup1 <mitchalsup@aol.com>:

The paragraaph with 3 >'s indicates malloc() cannot be written
in std. C. It used to be written in std. K&R C. I am not asking
if it is still in the std libraries, I am asking what happened
to make it impossible to write malloc() in std. C ?!?

 It's easy enough to write malloc() in standard C if your flavor of the
standard includes a way to ask the operating system for heap space.
Back in the old days it was sbrk().  Now it's mmap(MAP_ANON).
 

Note that these are in no way universal.  They might be common on some systems, but there are vast numbers of C implementations that are not used on POSIX or *nix type systems.
And while it is, I think, /possible/ to write a malloc() in pure portable standard C (plus something like sbrk), it is never done.  There are always advantages in using implementation-specific features for picking good sizes and alignments, handling locks for threading safety, using different algorithms with different balances between speed and compactness, and so on.

But I would be quite surprised if either of those ever made it into
any version of standard C.
 

Indeed.