3 ms·

That's still common today for subsequent interfaces as it makes it possible to write macros for preserving API compatibility. For example, to upgrade (struct st

by wahern 7y ago

That's still common today for subsequent interfaces as it makes it possible to write macros for preserving API compatibility. For example, to upgrade (struct stat).st_mtime to sub-second granularity you could do: #define st_mtime st_mtimensec.tv_sec POSIX preserves many prefixes for this reason. C99 brought anonymous unions (a Plan 9 invention), which makes many of these API tricks possible without using macros.

wahern 7y ago
Correction: C11 brought anonymous unions, which perhaps explains why they're not used in standard headers. Standard headers on most unix systems do make use of C99 features these days.
- asveikau 7y ago
  Thanks for looking that up, I didn't know the timeframe on that feature. I've known for a long time that Microsoft headers make use of anonymous unions, which makes it a rare case where they have implemented a recent ISO C feature ahead of time. I seem to recall GCC in the same timeframe would accept this with a warning that it's nonstandard. [I guess not anymore.]
  - wahern 7y ago
    In addition to C11's anonymous untagged members, struct foo { union { int i; double d; }; } Visual Studio also supports anonymous tagged members, union bar { int i; double d; }; struct foo { union bar; }; Is the latter more common in Microsoft land? I've always thought the latter were more useful and wished they were standardized. Anonymous tagged fields make it possible to reuse plain struct and union definitions, permitting a simple form of inheritance; whereas with untagged fields you have to rely on macros for sharing definitions. GCC (https://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html https://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html) and clang (confirmed macOS clang-1001.0.46.4) support anonymous tagged members with -fms-extensions, but I can't bring myself to make use of it as I still try to keep many of my projects working with Sun Studio and otherwise try to avoid non-standard features.
    - asveikau 7y ago
      > Is the latter more common in Microsoft land? I don't know if I have an authoritative sample on that. I saw it exactly once when I worked at MS and I thought it was weird. But I guess it aids in the "psuedo-inheritance" game that people play with structs and their first member being a "base class". Like GObject or gtk+ do. Or struct sockaddr, which duplicates the first few fields.

by wahern 7y ago

wahern 7y ago

Correction: C11 brought anonymous unions, which perhaps explains why they're not used in standard headers. Standard headers on most unix systems do make use of C99 features these days.

asveikau 7y ago
Thanks for looking that up, I didn't know the timeframe on that feature. I've known for a long time that Microsoft headers make use of anonymous unions, which makes it a rare case where they have implemented a recent ISO C feature ahead of time. I seem to recall GCC in the same timeframe would accept this with a warning that it's nonstandard. [I guess not anymore.]
- wahern 7y ago
  In addition to C11's anonymous untagged members, struct foo { union { int i; double d; }; } Visual Studio also supports anonymous tagged members, union bar { int i; double d; }; struct foo { union bar; }; Is the latter more common in Microsoft land? I've always thought the latter were more useful and wished they were standardized. Anonymous tagged fields make it possible to reuse plain struct and union definitions, permitting a simple form of inheritance; whereas with untagged fields you have to rely on macros for sharing definitions. GCC (https://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html https://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html) and clang (confirmed macOS clang-1001.0.46.4) support anonymous tagged members with -fms-extensions, but I can't bring myself to make use of it as I still try to keep many of my projects working with Sun Studio and otherwise try to avoid non-standard features.
  - asveikau 7y ago
    > Is the latter more common in Microsoft land? I don't know if I have an authoritative sample on that. I saw it exactly once when I worked at MS and I thought it was weird. But I guess it aids in the "psuedo-inheritance" game that people play with structs and their first member being a "base class". Like GObject or gtk+ do. Or struct sockaddr, which duplicates the first few fields.