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KPL
Guest
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| Function pointer in structs |
 Posted: Thu Nov 11, 2004 8:28 am |
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Ehm, I cant seem to make either of these two possibilites work (ver. 3.206):
| Code: |
typedef void (*resp_func_ptr)(char* a); /*!< Signature for all response functions */
typedef struct
{
char cmd[11];
resp_func_ptr resp_func;
int8 parameter;
}COMMANDSET; /*!< Common definition for module command sets */
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This compiles, but I get the following error message when I try to call the function:
Expecting function name
I try calling it like this:
| Code: |
(*(tmp_cmd_ptr+location[1])->resp_func)(str);
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(Ive tried several other attempts, include a local function pointer value, and copying the value of the struct f.ptr into that, to no use.
My other go looked like this:
| Code: |
typedef struct
{
char cmd[11];
void (*resp_func_ptr)(char* a);
int8 parameter;
}COMMANDSET; /*!< Common definition for module command sets */
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But this now I get an error message saying 'Unknown type' in the line with the function pointer definition.
Does anyone know what might be the problem? |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Thu Nov 11, 2004 8:49 am |
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Here's something I came up with for another poster
| Code: | /*****************************************************************************
This is an example of how to create a const array of function
pointers and call them. It is a bit of a trick to fool the compiler
but seems to work for the cases that I tested.
******************************************************************************/
#if defined(__PCM__)
#include <16f877.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#elif defined(__PCH__)
#include <18f452.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#endif
// Here is where we define the start of menu wrappers.
// !!!! Note that it (all wrapper addresses) must be within
// 1024 bytes of the caller
#define MENU_START_ADDRESS 0x200
// This is how many bytes the wrappers take up. You might have to
// set this value high and then determine how many the wrappers actually
// take up. Note that a BRA is usually used for small programs. However
// on a larger program a CALL instruction might be used which will
// require 2 additional bytes
#define FUNC_SIZE 8
// This is where we define our menu wrapper locations
#define MENU1_ADDRESS (MENU_START_ADDRESS)
#define MENU2_ADDRESS (MENU1_ADDRESS+FUNC_SIZE)
#define MENU3_ADDRESS (MENU2_ADDRESS+FUNC_SIZE)
#define MENU4_ADDRESS (MENU3_ADDRESS+FUNC_SIZE)
// Typedef for our function pointer
typedef int (*pFunc)(void);
// Typedef for our menu items
typedef struct {
char name[16];
int16 ptrFunc; // Just tricking the compiler here
} MenuItem;
// Here's that constant array for the menus
const MenuItem Menu[3]={{"String1", MENU1_ADDRESS},
{"String2", MENU2_ADDRESS},
{"String3", MENU3_ADDRESS}};
// These are the real Menus that we want to call
#org 0x2000,0x2100 // org'ed this just to show a CALL insteal of BRA
int RealMenuFunc1(void)
{
int i = 1;
return(i);
}
int RealMenuFunc2(void)
{
int i = 2;
return(i);
}
int RealMenuFunc3(void)
{
int i = 3;
return(i);
}
// These are wrapper menus to make setting the addresses easier.
// It also appears CCS is using a RCALL instruction which limits
// how far the menus can be away from the caller.
#org MENU1_ADDRESS, MENU1_ADDRESS + FUNC_SIZE - 1
int WrapperMenu1(void)
{
return(RealMenuFunc1());
}
#org MENU2_ADDRESS, MENU2_ADDRESS + FUNC_SIZE - 1
int WrapperMenu2(void)
{
return(RealMenuFunc2());
}
#org MENU3_ADDRESS, MENU3_ADDRESS + FUNC_SIZE - 1
int WrapperMenu3(void)
{
return(RealMenuFunc3());
}
void main()
{
int i;
pFunc ptrtofunc;
// Dummy initialization to keep the compiler from complaining
ptrtofunc = WrapperMenu1;
// Assign the address to the function pointer
ptrtofunc = (pFunc)Menu[0].ptrFunc;
// Call the function
i=(*ptrtofunc)();
ptrtofunc = (pFunc)Menu[1].ptrFunc;
i=(*ptrtofunc)();
ptrtofunc = (pFunc)Menu[2].ptrFunc;
i=(*ptrtofunc)();
while( TRUE )
{
}
}
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KPL
Guest
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| Posted: Thu Nov 11, 2004 8:53 am |
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Yeah, Ive been studying that thread a bit just now.
I dont think it would be worth it in this case though. Ill have several struct arrays and if I have to define and map out the location each its gonna take way too much time compared to my non-functionpointer solution.
But thanks though :D
Do you know if the code Trampas posted (right after yours) actually worked? |
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Guest
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| Posted: Thu Nov 11, 2004 8:59 am |
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| hmm, just read something another place..I guess you HAVE to let the compiler know the location of the function...sigh |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Thu Nov 11, 2004 9:00 am |
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| No, that is a niffty way of doing command parsers. He wanted to be able to do that so I came up with a way to do it by declaring function pointers. If you don't want to use the pointers, just put a const in there and then use a switch statement to call the proper function. |
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KPL
Guest
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| Posted: Thu Nov 11, 2004 3:46 pm |
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well, thats what Im doing now. Im gonna try your take on it tonight. Once again thanks!
Though this is gonna require a bit more work, and defeat my original intent of writing a system core that would enable modules to be developed rather independantly. |
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