How to explain this syntax?

How to explain this syntax?

[Andy]

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In gcc/gcc/testsuite/gcc.c-torture/compile/pr43635.c
we have

extern void d (void);

void (*foo (void)) (float)
{
  void (*(*x) (void)) (float) = d;
  return (*x) ();
}

d is a function without parameters and nothing returns.
foo is function without parameters and returns pointer to function with one
parameter float and also returning void?
what is type of x?
void (*(*x) (void)) (float) is on whole type definition of x or part is
type definition of x and part is cast d to x? which parts?
why not returns x but (*x) ()? don' t return pointer to function but call
this function?
I know, this is malignant example, in in real world can't be cast function
returning void to function returning value

Re: How to explain this syntax?

[Andrew Haley]

On 4/16/23 11:25, Andy via Gcc-help wrote:
> void (*(*x) (void)) (float)

declare x as pointer to function (void) returning pointer to function (float) returning void

https://cdecl.org/

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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Re: How to explain this syntax?

[Andy]

I meet odd struct + colon syntax:
in gcc/gcc/testsuite/gcc.c-torture/compile/init-3.c
is

struct something X = {
 foo: { },
 bar: 1,
};
bar:1 is one bit field? what means foo? is the same as
struct empty foo; where struct empty { };
colon is not only reserved to bitfields?

Second (init-2.c):
initializer

struct
{
  int e1, e2;
} v = { e2: 0 };
why not e2=0, colon instead of assign operator?

Re: How to explain this syntax?

[Xi Ruoyao]

On Wed, 2023-04-19 at 13:40 +0200, Andy via Gcc-help wrote:
> I meet odd struct + colon syntax:
> in gcc/gcc/testsuite/gcc.c-torture/compile/init-3.c
> is
> 
> struct something X = {
>  foo: { },
>  bar: 1,
> };
> bar:1 is one bit field? what means foo? is the same as
> struct empty foo; where struct empty { };
> colon is not only reserved to bitfields?

It's an obsoleted GNU extension:

https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html

> 
> Second (init-2.c):
> initializer
> 
> struct
> {
>   int e1, e2;
> } v = { e2: 0 };
> why not e2=0, colon instead of assign operator?

The point of the test case is ensuring GCC backward compatible with the
old extension, though it's obsoleted.

The GCC test cases are test cases, not some "material to learn C".

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University

Re: How to explain this syntax?

[Andy]

I don't learn C, but I am writing c90 Antlr grammar which should be as
compatible with GCC as possible.
I see many GNU extension, one is most significant is nested functions,
but all code is compilable with GCC with std=c90, not need std=gnu90,
although some code is compilable only with std=gnu90

Re: How to explain this syntax?

[Xi Ruoyao]

On Wed, 2023-04-19 at 14:35 +0200, Andy via Gcc-help wrote:
> I don't learn C, but I am writing c90 Antlr grammar which should be as
> compatible with GCC as possible.
> I see many GNU extension, one is most significant is nested functions,
> but all code is compilable with GCC with std=c90, not need std=gnu90,
> although some code is compilable only with std=gnu90

-pedantic-errors will reject most GNU extensions if you don't want them.

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University