Composite type

[icegood]

I'm reading now ISO/IEC 9899:TC2 draft and confusing about that composite type (6.2.7, in c11 same punt). I cannot get when such construction could be useful.

P.S. Sorry, it's rather pure c question but maybe in c++ the same story is.

[LB]

http://en.wikipedia.org/wiki/Composite_data_type
http://c0x.coding-guidelines.com/6.2.7.html (?)

Which part has you confused?

[Cubbi]

The standard's example is pretty self-explanatory:

if you declare a function as

int f(int (*)(), double (*)[3]);
(function taking a pointer to function that takes ANY number of arguments of any type and returns int, and a pointer to an array of three doubles)

and then declare it AGAIN as

int f(int (*)(char *), double (*)[]);
(function taking a pointer to function that takes one argument of type char* and returns int, and a pointer to an array of ANY number of doubles

then as far as the compiler is concerned, you just declared

int f(int (*)(char *), double (*)[3]);

so you can't call it with a pointer to an array of 5 doubles, for example (but you could the second function)

[icegood]

Cubbi, OK, so it's not about constructing new types but just control behaviour of old ones, right?

[LB]

The composite type is the result of putting the puzzle pieces together. The declarations could be in any order; one is not controlling the other.

[Cubbi]

It's about the compiler coming up with a type when faced with conflicting declarations for the same variable, and the rules it should follow to be conforming.