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Hello to all. I have some complex declarations to simplify with typedef I have done a try
1.
Why we don't use * symbol in the last statement in front of FUNC_PTR?Code:
char (*x[10]) (int);
/* typedef char FUNC(int);
typedef FUNC *FUNC_PTR;
FUNC_PTR x[10]; */
2.
I can't do this :/Code:
int (*x(int))[5]
3.
I have no way to see if I am right could you test my answers? and help me with the second? thank you :)Code:float *(*x(void))(int);
/* typedef float *FUNC(int);
FUNC *x(void); */
Seems silly, and it hasn't quite stuck in my head, but: C Right-Left Rule (Rick Ord's CSE 30 - UC San Diego)
And given that there exists a tool for unwinding declarations (and typedefs) into a type (cdecl) (originally command line, but now on the web!) you've got a way to check.
You mean thisQuote:
Originally Posted by tabstop
cdecl: C gibberish ↔ English
It doesn't take examples with typedef (syntax error).
That guy was my prof for that exact class, quite some years ago! Silly though it seems, I still remember that rule. Very good prof/class.Quote:
Originally Posted by tabstop
Here's another good explanation of how to read C declarations: Reading C type declarations.
To figure them out, start at the identifier and follow the precedence rules outwards. The main thing to remember about precedence here is that () and [] (function parens and array brackets) have the highest precedence. Of course, regular parens are used to alter this.
Code:char (*x[10]) (int);
/*
x x is
[] an array (of 10 elements)
* of pointers
() to functions (taking int)
char returning char
*/
typedef char(*FUNC)(int);
FUNC x1[10];
int (*x2(int))[5];
/*
x x is
() a function (taking int)
* returning a pointer
[] to an array (of 5 elements)
int of int
*/
typedef int (*ARRAY)[5];
ARRAY x3(int);
float *(*x4(void))(int);
/*
x x is
() a function (taking void)
* returning a pointer
() to a function (taking an int)
* returning a pointer
float to a float
*/
typedef float*(*FUNC2)(int);
FUNC2 x5(void);
Because you can't have a * as the left-most symbol in a declaration.Quote:
Originally Posted by Mr.Lnx
The way you were talking about it would expand to something like:
*char (*x[10]) (int);
Which is not valid C syntax
The * symbol is embedded in the definition of FUNC_PTR (which is a FUNC *). Note, this has something to do with operator precedence. The [10] is processed before the *. Expand it one layer at a time
x is an array of 10 FUNC_PTRs
x is an array of 10 (pointer to FUNC or FUNC *) -- there is your *
x is an array of 10 (pointer to (function taking int and returning char))
Those appear to be the same. What makes you think they aren't? If they truly are the same, then you can redeclare x as both types (the typedef'ed and non-typedef'ed) and the compiler shouldn't care. When I compile the following program, I get no errors:Quote:
Originally Posted by Mr.Lnx
But if I make a small change to FUNC, so it returns float instead of float *, I get the following error:Code:$ cat foo.c
typedef float *FUNC(int);
int main(void)
{
float *(*x(void))(int);
FUNC *x(void);
return 0;
}
$ make foo
gcc -Wall -ggdb3 -pedantic -std=c99 -O0 -o foo foo.c -lm -lpthread -lrt
$
EDIT: I don't know if you actually had a question about your number 2.Code:$ cat foo.c
typedef float FUNC(int);
int main(void)
{
float *(*x(void))(int);
FUNC *x(void);
return 0;
}
$ make foo
gcc -Wall -ggdb3 -pedantic -std=c99 -O0 -o foo foo.c -lm -lpthread -lrt
foo.c: In function ‘main’:
foo.c:6:11: error: conflicting types for ‘x’
foo.c:5:14: note: previous declaration of ‘x’ was here
make: *** [foo] Error 1
If it's giving you problems, you may be missing a semicolon at the end (or you just didn't copy it)Code:int (*x(int))[5]
Throwing my $.02 in the ring as well: https://cboard.cprogramming.com/showthread.php?p=1164489
@anduril thank you. So I was right =D
Yes now it is clear!
I have seen the following :
I think it can be with less statements as ogabooga wrote you can use one typedef to simplify a complex declaration at the same who some other can use two statements or more typedef'sCode:
int *(*x[10])(void);
typedef int *Fcn(void);
typedef Fcn *Fcn_ptr;
typedef Fcn_ptr Fcn_ptr_array[10];
Fcn_ptr_array x;