Simple struct definition error

hotwheelharry · 11-06-2009, 07:43 PM

Hello all, I am new to C and have a small problem.
I have defined the Console struct as follows...

Code:

typedef struct
{ 
  //console properties
  int Number;
  void (*Hide)(Console *);
  void (*Show)(Console *);
  short x;
  short y;
  short width;
  short height;
} Console;

but I get the following error...

"Line 5: Expected ')' before '*' token"

That is on the Hide function pointer line next to the last * star thing (@ char 23).
I don't understand why, I thought that's how to define a function pointer in a struct that takes a pointer as an argument.

If it makes any difference, this is going to be a program for a TI89 calculator.

Thanks

quzah · 11-06-2009, 08:20 PM

You can't use Console * inside the structure that defines Console in the first place. You need to typedef it first.

Quzah.

hotwheelharry · 11-06-2009, 09:01 PM

like...

Code:

typedef Console* ConsoleRef;

typedef struct
{ 
  //console properties
  int Number;
  void (*Hide)(ConsoleRef);
  void (*Show)(ConsoleRef);
  short x;
  short y;
  short width;
  short height;
} Console;

How exactly did you mean?

MisterIO · 11-06-2009, 09:23 PM

Quote:

Originally Posted by hotwheelharry

like...

Code:

typedef Console* ConsoleRef;

typedef struct
{ 
  //console properties
  int Number;
  void (*Hide)(ConsoleRef);
  void (*Show)(ConsoleRef);
  short x;
  short y;
  short width;
  short height;
} Console;

How exactly did you mean?

You're doing a typedef of struct "nothing" to console.
And the first typedef doesn't work.
An example that works:

Code:

#include <stdio.h>

struct console;
typedef struct console *console_ptr;

typedef struct console {
	int a;
	console_ptr c_p;
} console;

int main(void)
{
	console c = {.a = 0, .c_p = NULL,};
	printf("c.a = %d\n", c.a);
	return 0;
}

Also those are not references, which don't even exist in c, but pointers.

C_ntua · 11-07-2009, 01:08 AM

Code:

typedef struct myConsole
{ 
  ...
  struct myConsole* cpointer;
  ...
} Console;

Or do this. You have normally a struct myConsole and you name that struct "Console". Now you can use it as Console instead of "struct myConsole".

In case you are wondering, you cannot replace above "struct myConsole*" with "Console*" inside the struct, cause it has not yet beend typedef.

Elysia · 11-07-2009, 05:37 AM

Please don't typedef pointers like this. They obfuscate the code!
Is it really that difficult to type out the * to make it a pointer type?

MisterIO · 11-07-2009, 09:23 AM

Quote:

Originally Posted by Elysia

Please don't typedef pointers like this. They obfuscate the code!
Is it really that difficult to type out the * to make it a pointer type?

IMO there's no point in doing the typedef of struct console either, unless he wants to create an opaque type(which wouldn't make it necessary, but sometimes it's used).

MK27 · 11-07-2009, 10:18 AM

Quote:

Originally Posted by MisterIO

IMO there's no point in doing the typedef of struct console either, unless he wants to create an opaque type(which wouldn't make it necessary, but sometimes it's used).

Gotta disagree with that if you mean that of these two:

Code:

typdef struct console;
struct console;

you prefer the later. But I do agree with Elysia about not including a * in typedef's.

11-06-2009, 07:43 PM	#1
hotwheelharry Registered User Join Date: Nov 2009 Posts: 2	Simple struct definition error Hello all, I am new to C and have a small problem. I have defined the Console struct as follows... Code: typedef struct { //console properties int Number; void (Hide)(Console ); void (Show)(Console ); short x; short y; short width; short height; } Console; but I get the following error... "Line 5: Expected ')' before '' token" That is on the Hide function pointer line next to the last star thing (@ char 23). I don't understand why, I thought that's how to define a function pointer in a struct that takes a pointer as an argument. If it makes any difference, this is going to be a program for a TI89 calculator. Thanks
hotwheelharry is offline

11-06-2009, 08:20 PM	#2
quzah +++ OK NO CARRIER Join Date: Oct 2001 Posts: 10,260	You can't use Console * inside the structure that defines Console in the first place. You need to typedef it first. Quzah. __________________ Hundreds of thousands of dipshits can't be wrong. Are you up for the suck?
quzah is offline

11-06-2009, 09:01 PM	#3
hotwheelharry Registered User Join Date: Nov 2009 Posts: 2	like... Code: typedef Console* ConsoleRef; typedef struct { //console properties int Number; void (Hide)(ConsoleRef); void (Show)(ConsoleRef); short x; short y; short width; short height; } Console; How exactly did you mean? Last edited by hotwheelharry; 11-06-2009 at 09:04 PM.
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11-07-2009, 01:08 AM	#5
C_ntua Registered User Join Date: Jun 2008 Posts: 1,134	Code: typedef struct myConsole { ... struct myConsole* cpointer; ... } Console; Or do this. You have normally a struct myConsole and you name that struct "Console". Now you can use it as Console instead of "struct myConsole". In case you are wondering, you cannot replace above "struct myConsole" with "Console" inside the struct, cause it has not yet beend typedef.
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