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future
Joined: 14 May 2004
Posts: 330
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| loading structs with pointers to function |
 Posted: Sat Sep 16, 2006 5:10 pm |
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Hi,
I am trying to implement a basic menu system that I think it should work, but does not.
This is the most basic code that shows the problem.
| Code: | #include <18f452.h>
#device adc=8
#use delay( clock=40000000 )
#fuses H4, NOWDT, PUT, NOLVP//, CPD, PROTECT, CPB, WRT, WRTC, BROWNOUT
#use rs232( baud=19200, parity = n, xmit = pin_c6, rcv = pin_c7, bits = 8 )
#zero_ram
#use rtos( timer=3, minor_cycle=5ms )
#case
char b1, b2, menu;
typedef void (*function_ptr)();
void inc_b1() { b1++; }
void dec_b1() { b1--; }
void inc_b2() { b2++; }
void dec_b2() { b2--; }
void menu1() { printf( "\n\rMenu #1 b1=%03u", b1 ); }
void menu2() { printf( "\n\rMenu #2 b2=%03u", b2 ); }
struct
{
function_ptr menu_routine;
char menu_previous;
char menu_next;
function_ptr inc_routine;
function_ptr dec_routine;
}
main_screen_config[2] = { { menu1, 0, 1, inc_b1, dec_b1 } ,
{ menu2, 1, 2, inc_b2, dec_b2 } };
main()
{
function_ptr test;
menu=0;
test = menu1; // here test has the correct address
(*test)(); //call function
test = main_screen_config[menu].inc_routine; // test becomes NULL here
test = main_screen_config[0].inc_routine; // test is still NULL
printf( "b1 value= %u", b1 );
} |
The pointer 'test' can not load the correct function address from the struct, or the struct is not being loaded at all...
Compiler version is 249.
Thank you in advance for any suggestions. |
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Ttelmah
Guest
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| Posted: Sun Sep 17, 2006 3:29 am |
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The problem is that you cannot initialise a structure during compile time, with the function addresses. You will find the structure entries contain 0' for each pointer. You need to manually initialise the structure at the start of the program with the addresses to use. Also, the compiler doesn't actually 'instance' the pointer, till it 'sees' it as having been accessed. Unfortunately writing it to a structure, doesn't seem to trigger this...
So, (to allow the other values to be initialised during compiler time), change the pointer to an int16, and use something (bulky), like:
| Code: |
struct
{
int16 menu_routine;
char menu_previous;
char menu_next;
int16 inc_routine;
int16 dec_routine;
}
main_screen_config[2] = { { 0, 0, 1, 0, 0 } ,
{ 0, 1, 2, 0, 0 } };
main()
{
function_ptr test;
menu=0;
test=menu1;
main_screen_config[0].menu_routine=test;
test=inc_b1;
main_screen_config[0].inc_routine=test;
test=dec_b1;
main_screen_config[0].dec_routine=test;
test=menu2;
main_screen_config[1].menu_routine=test;
test=inc_b2;
main_screen_config[1].inc_routine=test;
test=dec_b2;
main_screen_config[1].dec_routine=test;
test = menu1; // here test has the correct address
(*test)(); //call function
test = main_screen_config[menu].inc_routine;
test = main_screen_config[0].inc_routine;
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The 'stupid' thing, is that whatever type you declare the structure variable to be, it'll complain about an 'invlaid type conversion', if you try to write the address to it, yet if you go 'via' a temporary variable, it'll accept it (and work...).
Best Wishes |
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future
Joined: 14 May 2004
Posts: 330
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| Posted: Sun Sep 17, 2006 1:09 pm |
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This is bad... The code will look ugly as the menu size grows up.
I was hoping to have up to like 30 menus.
I remember seeing arrays initialized like this on the forum... maybe I could put all the menu structure in rom and copy to ram struct at runtime.
Thank you. |
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