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It may be unusable for “modern” operating systems (you could write an early UNIX clone with just ISO C because early UNIX didn’t support much). But that’s basi

It may be unusable for “modern” operating systems (you could write an early UNIX clone with just ISO C because early UNIX didn’t support much). But that’s basically always been the case. I doubt you could stay within the first ISO C standard and write a modern operating system.

phicoh 5y ago
Assuming that an early Unix clone would be written in C plus some amount of assembler. Then what constructs of modern Unix systems make it impossible to in write in the first ISO C standard plus some assembler? For example, 4.4BSD, early Solaris have just about everything you would expect in a modern operating system. And give the age of those systems, they were written in early versions of the C standard.
- immibis 5y ago
  This is true for any language. An operating system can be written in Java plus some amount of assembler.
- ErikCorry 5y ago
  Before 1985 there was no C standard, and until 1989 it was only a draft. So I doubt anything was written in standard C in the 1970s or early 1980s.
  - phicoh 5y ago
    C89 is mostly a superset of K&R C. So if you can write an OS in K&R you can write it is C89. The issue was, do modern operating systems require newer versions of the C standard? Or can you write everything in C89.
    - pjmlp 5y ago
      Inline assembly is not part of C89, so a pure C89 compiler needs to rely on an external Assembler for systems programming for example. Same applies to using C in hardware that lacked memory mapped IO.
    - ErikCorry 5y ago
      K&R wasn't standardized either though.
- maxlybbert 5y ago
  (Duplicating an answer to a similar question): The C standard has notes about a freestanding implementation, mainly for developing kernels. The requirements C has for freestanding environments are very limited ( http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf , you get float.h, iso646.h, limits.h, stdalign.h, stdarg.h, stdbool.h, stddef.h, stdint.h, and stdnoreturn.h) and the starting point for the program is implementation defined; you might get _Atomic, but that’s optional). For the record, C++ goes a little overboard and promises all sorts of things in its freestanding environment. https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5iO3keCMJ https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5i...
andyjohnson0 5y ago
> I doubt you could stay within the first ISO C standard and write a modern operating system. Do you take that view because of some intrinsic deficiency in the language, or the difficulty of memory safety, or something else?
- maxlybbert 5y ago
  The C standard has notes about a freestanding implementation, mainly for developing kernels. The requirements C has for freestanding environments are very limited ( http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf , you get float.h, iso646.h, limits.h, stdalign.h, stdarg.h, stdbool.h, stddef.h, stdint.h, and stdnoreturn.h) and the starting point for the program is implementation defined; you might get _Atomic, but that’s optional). For the record, C++ goes a little overboard and promises all sorts of things in its freestanding environment. https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5iO3keCMJ https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5i...

phicoh 5y ago

Assuming that an early Unix clone would be written in C plus some amount of assembler. Then what constructs of modern Unix systems make it impossible to in write in the first ISO C standard plus some assembler? For example, 4.4BSD, early Solaris have just about everything you would expect in a modern operating system. And give the age of those systems, they were written in early versions of the C standard.

immibis 5y ago
This is true for any language. An operating system can be written in Java plus some amount of assembler.
ErikCorry 5y ago
Before 1985 there was no C standard, and until 1989 it was only a draft. So I doubt anything was written in standard C in the 1970s or early 1980s.
- phicoh 5y ago
  C89 is mostly a superset of K&R C. So if you can write an OS in K&R you can write it is C89. The issue was, do modern operating systems require newer versions of the C standard? Or can you write everything in C89.
  - pjmlp 5y ago
    Inline assembly is not part of C89, so a pure C89 compiler needs to rely on an external Assembler for systems programming for example. Same applies to using C in hardware that lacked memory mapped IO.
  - ErikCorry 5y ago
    K&R wasn't standardized either though.
maxlybbert 5y ago
(Duplicating an answer to a similar question): The C standard has notes about a freestanding implementation, mainly for developing kernels. The requirements C has for freestanding environments are very limited ( http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf , you get float.h, iso646.h, limits.h, stdalign.h, stdarg.h, stdbool.h, stddef.h, stdint.h, and stdnoreturn.h) and the starting point for the program is implementation defined; you might get _Atomic, but that’s optional). For the record, C++ goes a little overboard and promises all sorts of things in its freestanding environment. https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5iO3keCMJ https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5i...

andyjohnson0 5y ago

> I doubt you could stay within the first ISO C standard and write a modern operating system. Do you take that view because of some intrinsic deficiency in the language, or the difficulty of memory safety, or something else?

maxlybbert 5y ago
The C standard has notes about a freestanding implementation, mainly for developing kernels. The requirements C has for freestanding environments are very limited ( http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf , you get float.h, iso646.h, limits.h, stdalign.h, stdarg.h, stdbool.h, stddef.h, stdint.h, and stdnoreturn.h) and the starting point for the program is implementation defined; you might get _Atomic, but that’s optional). For the record, C++ goes a little overboard and promises all sorts of things in its freestanding environment. https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5iO3keCMJ https://groups.google.com/g/comp.std.c/c/zzyii-DlMiU/m/RnH5i...