Simplify complex declarations using typedef.

[Mr.Lnx]

Hello to all. I have some complex declarations to simplify with typedef I have done a try

1.

 
char (*x[10]) (int);

/* typedef char FUNC(int);
   typedef FUNC *FUNC_PTR;
   FUNC_PTR x[10]; */

Why we don't use * symbol in the last statement in front of FUNC_PTR?

2.

 
int (*x(int))[5]

I can't do this :/

3.

float *(*x(void))(int); 

/* typedef float *FUNC(int);
    FUNC *x(void); */

I have no way to see if I am right could you test my answers? and help me with the second? thank you

[tabstop]

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.

[Mr.Lnx]

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 this

cdecl: C gibberish ↔ English

It doesn't take examples with typedef (syntax error).

[anduril462]

Seems silly, and it hasn't quite stuck in my head, but: C Right-Left Rule (Rick Ord's CSE 30 - UC San Diego)

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.

Here's another good explanation of how to read C declarations: Reading C type declarations.

[oogabooga]

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.

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);

[anduril462]

Hello to all. I have some complex declarations to simplify with typedef I have done a try

1.

 
char (*x[10]) (int);

/* typedef char FUNC(int);
   typedef FUNC *FUNC_PTR;
   FUNC_PTR x[10]; */

Why we don't use * symbol in the last statement in front of FUNC_PTR?

Because you can't have a * as the left-most symbol in a declaration.
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))

3.

float *(*x(void))(int); 

/* typedef float *FUNC(int);
    FUNC *x(void); */

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:

$ 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
$

But if I make a small change to FUNC, so it returns float instead of float *, I get the following error:

$ 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

EDIT: I don't know if you actually had a question about your number 2.

int (*x(int))[5]

If it's giving you problems, you may be missing a semicolon at the end (or you just didn't copy it)

[whiteflags]

Throwing my $.02 in the ring as well: https://cboard.cprogramming.com/showthread.php?p=1164489

[Mr.Lnx]

@anduril thank you. So I was right =D

Yes now it is clear!

I have seen the following :

int *(*x[10])(void);

typedef int *Fcn(void);
typedef Fcn *Fcn_ptr;
typedef Fcn_ptr Fcn_ptr_array[10];
Fcn_ptr_array x;

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's