The Linux Kernel Looks to "Bite the Bullet" in Enabling Microsoft C Extensions
6 comments
·November 10, 2025unwind
Huh. I thought the article was vague on what exactly these extensions permit, so I'd thought I'd look up the GNU documentation. Surprisingly, it [1] was rather vague too!
The only concrete example is:
Accept some non-standard constructs used in Microsoft header files.
In C++ code, this allows member names in structures to be similar to previous types declarations.
typedef int UOW;
struct ABC {
UOW UOW;
};
messe
The important one is "Unnamed Structure and Union Fields"[1], in particular unnamed structs and union fields without a tag.
ISO C11 and onward allows for this:
struct {
int a;
union {
int b;
float c;
};
int d;
} foo;
struct {
int a;
union bar {
int b;
float c;
};
int d;
} foo;
struct {
int a;
union bar;
int d;
} foo;
struct parent {
int i;
void *p;
};
void parent_do_something(struct parent *p);
struct child {
struct parent;
const char *s;
};
struct child *c;
struct parent *p = (struct child *)c; // valid
parent_do_something(p);
c.i++; // valid
creshal
Why is this still not standardized?
arguflow
A really good example of it is in this lore thread here [1]. He explains it better than me so I'll just link it here
[1]: https://lore.kernel.org/lkml/200706301813.58435.agruen@suse....
mrlonglong
Microsoft "embrace, extend and takeover" comes to mind here. Caveat emptor.
> though some may feel the wrong way around Microsoft C behavior being permitted
The same extension can be enabled with `-fplan9-extensions`, might be more appealing to some!