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Problem using a function pointer

 
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bastirn



Joined: 08 Jan 2020
Posts: 17

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Problem using a function pointer
PostPosted: Wed Jan 08, 2020 7:21 am     Reply with quote

Hello,

I'm trying to implement a shell in a PIC16F1829.
I'm stuck while i try to call a function using function pointer.
You can see a resumé of the problem.

Thanks in advance for any answer,

Best regards,
Bastien NICAUD

Code:

#include <16F1829.h>
#device PIC16F1829
#device PIC16F1829 *=16
#device ANSI
#DEVICE PASS_STRINGS=IN_RAM

#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <stdarg.h>
#include <stdbool.h>

#include "bnishell.h"

#DEVICE CONST=ROM

#fuses INTRC_IO         // Internal OSC

#use delay (clock=32M)
#use rs232(baud=115200, xmit=PIN_C4, rcv=PIN_C5, stream=PC)

int cmd_test(int argc, char ** argv)
{
  printf("\n\rtest\n\r");
  return SHELL_RET_SUCCESS;
}

void main(){

    char *cmd_test_argv;
    char **cmd_test_argv2;

    cmd_test_argv = 81;
    cmd_test_argv2 = &cmd_test_argv ;

    int (*toto)(int, char **);
    int zz ;

    enable_interrupts(INT_RDA);
    enable_interrupts(GLOBAL);

    //shell_init();
    //shell_register(&cmd_test, "permet de tester", "0-1", "test");

    toto = cmd_test;

    zz = cmd_test(1,cmd_test_argv2);  // Works but not what we need

    // What we want to do :
    zz = (*toto)(1,cmd_test_argv2);   // Error return : "No valid assignment made to function pointer" in the .err file
   
    printf("%d",zz);
    while (1) {
        //shell_task();
    }
 
}
Ttelmah



Joined: 11 Mar 2010
Posts: 19195

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PostPosted: Wed Jan 08, 2020 9:25 am     Reply with quote

The problem isn't where you think it is.
It's actually the cmd_test_argv2;
Change the ** declarations to:

int (*toto)(int a, char *b[]);

and the same for the function declaration. CCS does not 'like' pointers
to pointers, but happily accepts pointers to arrays (which give exactly
the same effect).
You need to put a dummy variable name to do this (as I show)
bastirn



Joined: 08 Jan 2020
Posts: 17

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PostPosted: Thu Jan 09, 2020 8:49 am     Reply with quote

Hello,

Thank you for you answer, now there is no more compilation error,
unfortunately it doesn't work as i want ...
Here is the code that i used :

Code:

#include <16LF1829.h>
//#device PIC16F1829
#device PIC16LF1829 *=16
#device ANSI
#DEVICE PASS_STRINGS=IN_RAM

#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <stdarg.h>
#include <stdbool.h>

//#include "bnishell.h"

#DEVICE CONST=ROM

#fuses INTRC_IO         // Internal OSC

#use delay (clock=32M)
#use rs232(baud=115200, xmit=PIN_C4, rcv=PIN_C5, stream=PC)

int cmd_test(int argc, char * argv[])
{
    printf("\n\rtest\n\r");
    printf("\n\r %04X \n\r",&argv);
    return 1;
}

void main(){

    delay_ms(20);

    char *cmd_test_argv;
    char *cmd_test_argv2[];

    int (*toto)(int a, char *b[]);
    int zz ;

    cmd_test_argv = 81;
    cmd_test_argv2 = &cmd_test_argv ;

    toto = cmd_test;

    //zz = cmd_test(1,cmd_test_argv2);  // Works but not what we need

    zz = (*toto)(1,cmd_test_argv2);
   
    printf("\n\r %04X \n\r",&cmd_test_argv2);
    while (1) {
    }
 
}


I should have the same adress resulting of this two printf but they are different. Any suggestion ?

Thanks in advance for any answer,
Best regards
Bastien
Ttelmah



Joined: 11 Mar 2010
Posts: 19195

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PostPosted: Thu Jan 09, 2020 9:28 am     Reply with quote

It won't.

& means 'give the address of'. Called in the subroutine, this gives the
address of the _temporary_ variable holding the value. Not the address
of the original variable.
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