This discussion has been locked.

You can no longer post new replies to this discussion. If you have a question you can start a new discussion

C182 error kicking my butt

Hopefully this makes sense. I've cut down the actual code to make this short.

I have a series of strings as shown:


char code Num1[] =  {"One  "};
char code Num2[] =  {"Two  "};
char code Num3[] =  {"Three"};

I then have an array of pointers that have all the address of the start of those strings:

code char code *CHNLTable[] = { Num1, Num2, Num3};

I then have a pointer in a function that I want to assign to an element in the array and I get a C182 "Pointer to different objects" warning.

void func(void){	
  unsigned int *myptr;
   myptr = &CHNLTable;

   ...code that uses myptr

}

I don't understand the warning AND the code seems to work fine. Can someone explain to me the dumb thing I'm doing??

Parents

0 Jon Ward over 23 years ago in reply to Tony Karavidas

Oh...Just ask...

Here's what I came up with.

#include <stdio.h>
#include <reg51.h>

char code Num1[] =  {"One  "};
char code Num2[] =  {"Two  "};
char code Num3[] =  {"Three"};

// Num1, 2, and 3 are arrays (in code) of characters (strings).

code char code *CHNLTable[] = { Num1, Num2, Num3};

// CHNLTable is an array of pointers (in code) to characters (in code)
// So, each element takes 2 bytes (because the pointer is a code pointer)

void main (void)
{
unsigned int *myptr;
// myptr is a pointer to an unsigned int (a generic, 3-byte pointer)

myptr = &CHNLTable;
// I'm not sure what myptr should point to...
// the strings or the pointers to the strings...
// so, I'm inclined to say this is probably wrong...
// It yields this warning:
// *** WARNING C182 IN LINE 21 OF MAIN.C: pointer to different objects


// Setup the serial port (stolen from HELLO.C)
SCON  = 0x50;
TMOD |= 0x20;
TH1   = 221;
TR1   = 1;
TI    = 1;


// Here's one of my interpretations of this...
  {
  char code *jons_ptr;

// jons_ptr is a pointer to a character in code space
// so, the sizeof jons_ptr is 2

  jons_ptr = CHNLTable[0];   // jons_ptr points to the string "One  "
  printf ("jons_ptr = %s\n", jons_ptr); // This prints it

  jons_ptr = CHNLTable[1];   // jons_ptr points to the string "Two  "
  printf ("jons_ptr = %s\n", jons_ptr); // This prints it

// If you are trying to get a pointer to an individual string...
// this is the way to do it...
  }

// Here's another interpretation...
  {
  char code * code *jons_dptr;

// jons_dptr is a ptr to a ptr (in code space) to a char in code space
// I think this is more like what we really want to get!
// the sizeof jons_dptr is 2

  jons_dptr = CHNLTable;
// jons_dptr points to the ptr to the string "One  "

  printf ("*jons_dptr = %s\n", *jons_dptr);
// *jons_dptr points to the string "One  "

  jons_dptr++;
// Increment jons_dptr so that it points to the ptr to the string "Two  "

  printf ("*jons_dptr = %s\n", *jons_dptr);
  }

while (1);  
}

// Viola!!!

I tested this with uVision2 V6.21 and got the results that I expected.

The real problem in the original code (which I think I kept intact) is a clear definition of what you want to point to (the string or the table).

If you use a table and you want to get a pointer to it, you need to remember that [] => *. In other words a pointer to an array of pointers is really a double pointer (or a pointer to a pointer to a thing).

Jon

Reply

0 Jon Ward over 23 years ago in reply to Tony Karavidas

Oh...Just ask...

Here's what I came up with.

#include <stdio.h>
#include <reg51.h>

char code Num1[] =  {"One  "};
char code Num2[] =  {"Two  "};
char code Num3[] =  {"Three"};

// Num1, 2, and 3 are arrays (in code) of characters (strings).

code char code *CHNLTable[] = { Num1, Num2, Num3};

// CHNLTable is an array of pointers (in code) to characters (in code)
// So, each element takes 2 bytes (because the pointer is a code pointer)

void main (void)
{
unsigned int *myptr;
// myptr is a pointer to an unsigned int (a generic, 3-byte pointer)

myptr = &CHNLTable;
// I'm not sure what myptr should point to...
// the strings or the pointers to the strings...
// so, I'm inclined to say this is probably wrong...
// It yields this warning:
// *** WARNING C182 IN LINE 21 OF MAIN.C: pointer to different objects


// Setup the serial port (stolen from HELLO.C)
SCON  = 0x50;
TMOD |= 0x20;
TH1   = 221;
TR1   = 1;
TI    = 1;


// Here's one of my interpretations of this...
  {
  char code *jons_ptr;

// jons_ptr is a pointer to a character in code space
// so, the sizeof jons_ptr is 2

  jons_ptr = CHNLTable[0];   // jons_ptr points to the string "One  "
  printf ("jons_ptr = %s\n", jons_ptr); // This prints it

  jons_ptr = CHNLTable[1];   // jons_ptr points to the string "Two  "
  printf ("jons_ptr = %s\n", jons_ptr); // This prints it

// If you are trying to get a pointer to an individual string...
// this is the way to do it...
  }

// Here's another interpretation...
  {
  char code * code *jons_dptr;

// jons_dptr is a ptr to a ptr (in code space) to a char in code space
// I think this is more like what we really want to get!
// the sizeof jons_dptr is 2

  jons_dptr = CHNLTable;
// jons_dptr points to the ptr to the string "One  "

  printf ("*jons_dptr = %s\n", *jons_dptr);
// *jons_dptr points to the string "One  "

  jons_dptr++;
// Increment jons_dptr so that it points to the ptr to the string "Two  "

  printf ("*jons_dptr = %s\n", *jons_dptr);
  }

while (1);  
}

// Viola!!!

Children

No data