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Gavin Pinto



Joined: 18 Oct 2009
Posts: 27
Location: Australia

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PostPosted: Tue Feb 09, 2010 12:47 pm     Reply with quote
Wayne_ wrote:
Well, my compiler works differently to yours.

Sizeof(strings) = 8; // This is a pointer array. Each index contains a pointer to the string which is sizeof(char *) 2 bytes. so strings is 8 bytes in size.

sizeof(char *) = 2;

From the lst file
Code:

.................... a = sizeof(strings);
*
00AB:  MOVLW  08
00AC:  MOVWF  27
.................... b = sizeof(char *);
00AD:  MOVLW  02
00AE:  MOVWF  28
.................... i = sizeof(strings) / sizeof(char *);
00AF:  MOVLW  04
00B0:  MOVWF  29


The fomula
i = sizeof(strings) / sizeof(char *); returns 4 which is the number of null terminated strings in the pointer array strings. Which is correct.

Show me your .lst code where
"sizeof(strings) evaluates to 4"
Or did you work it out some other way ?



Here is my listing
Code:

.................... rom char* ptr;
.................... 
.................... rom char *strings[] = 
.................... { 
....................    "HELLO", 
....................    "WORLD", 
....................    "CONST", 
....................    "STRINGS" 
.................... }; 
0EB62:  MOVLW  48
0EB64:  MOVWF  xDA
0EB66:  MOVLW  45
0EB68:  MOVWF  xDB
0EB6A:  MOVLW  4C
0EB6C:  MOVWF  xDC
0EB6E:  MOVWF  xDD
0EB70:  MOVLW  4F
0EB72:  MOVWF  xDE
0EB74:  CLRF   xDF
0EB76:  MOVLW  57
0EB78:  MOVWF  xE0
0EB7A:  MOVLW  4F
0EB7C:  MOVWF  xE1
0EB7E:  MOVLW  52
0EB80:  MOVWF  xE2
0EB82:  MOVLW  4C
0EB84:  MOVWF  xE3
0EB86:  MOVLW  44
0EB88:  MOVWF  xE4
0EB8A:  CLRF   xE5
0EB8C:  MOVLW  43
0EB8E:  MOVWF  xE6
0EB90:  MOVLW  4F
0EB92:  MOVWF  xE7
0EB94:  MOVLW  4E
0EB96:  MOVWF  xE8
0EB98:  MOVLW  53
0EB9A:  MOVWF  xE9
0EB9C:  MOVLW  54
0EB9E:  MOVWF  xEA
0EBA0:  CLRF   xEB
0EBA2:  MOVLW  53
0EBA4:  MOVWF  xEC
0EBA6:  MOVLW  54
0EBA8:  MOVWF  xED
0EBAA:  MOVLW  52
0EBAC:  MOVWF  xEE
0EBAE:  MOVLW  49
0EBB0:  MOVWF  xEF
0EBB2:  MOVLW  4E
0EBB4:  MOVWF  xF0
0EBB6:  MOVLW  47
0EBB8:  MOVWF  xF1
0EBBA:  MOVLW  53
0EBBC:  MOVWF  xF2
0EBBE:  CLRF   xF3
0EBC0:  MOVLW  08
0EBC2:  MOVWF  xD3
0EBC4:  MOVLW  DA
0EBC6:  MOVWF  xD2
0EBC8:  MOVLW  08
0EBCA:  MOVWF  xD5
0EBCC:  MOVLW  E0
0EBCE:  MOVWF  xD4
0EBD0:  MOVLW  08
0EBD2:  MOVWF  xD7
0EBD4:  MOVLW  E6
0EBD6:  MOVWF  xD6
0EBD8:  MOVLW  08
0EBDA:  MOVWF  xD9
0EBDC:  MOVLW  EC
0EBDE:  MOVWF  xD8
.................... 
.................... a= sizeof(strings);
0EBE0:  MOVLW  04
0EBE2:  MOVWF  xC3
.................... b=sizeof(ptr);
0EBE4:  MOVWF  xC4
.................... c=sizeof(strings)/sizeof(ptr);
0EBE6:  MOVLW  01
0EBE8:  MOVWF  xC5
....................

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Gavin Pinto



Joined: 18 Oct 2009
Posts: 27
Location: Australia

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PostPosted: Wed Feb 10, 2010 4:52 pm     Reply with quote
Wayne_ wrote:
Well, my compiler works differently to yours.

Or did you work it out some other way ?


So whose compiler is doing the right thing?
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Wayne_



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Posts: 681

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PostPosted: Thu Feb 11, 2010 3:32 am     Reply with quote
.................... ROM char *strings[] =
.................... {
.................... "HELLO",
Code:

....................    "WORLD",
....................    "CONST",
....................    "STRINGS"
.................... }; 
.................... ROM char *ptr;
.................... ROM char *ptr2[1];
.................... const char *ptr3 = 0;
.................... char *ptr4;
.................... 
.................... void main()
.................... {
*
0099:  CLRF   04
009A:  BCF    03.7
009B:  MOVLW  1F
009C:  ANDWF  03,F
009D:  BSF    03.5
009E:  BSF    1F.0
009F:  BSF    1F.1
00A0:  BSF    1F.2
00A1:  BCF    1F.3
00A2:  MOVLW  07
00A3:  MOVWF  1C
.................... //char k;
.................... int oldportc;
.................... int newportc;
.................... int a, b, c, d, e, f, i;
.................... 
.................... a = sizeof(strings);
*
00AB:  MOVLW  08
00AC:  MOVWF  29
.................... b = sizeof(char *);
00AD:  MOVLW  02
00AE:  MOVWF  2A
.................... c = sizeof(ptr);   // ROM char *ptr;
00AF:  MOVLW  01
00B0:  MOVWF  2B
.................... d = sizeof(ptr2);   // ROM char *ptr2[1];
00B1:  MOVLW  02
00B2:  MOVWF  2C
.................... e = sizeof(ptr3);   // const char *ptr3;
00B3:  MOVWF  2D
.................... f = sizeof(ptr4);   // char *ptr4;
00B4:  MOVWF  2E
.................... i = sizeof(strings) / sizeof(char *);
00B5:  MOVLW  04
00B6:  MOVWF  2F

The problem or feature appears to be related to a ROM char * pointer.
If you define a single pointer ROM char *ptr; then it has a size of 1, if you define an array of pointers ROM char *ptr[1]; or ROM char *ptr = {"fred"}; and it has a size of at least 1 then the size of ptr is 2.

So I have no idea why ? But the example doesn't refer to the size of the ptr.

As the routine requires the number of strings in the array then the formula in my case needs to return a value of 4.

In your case
sizeof(strings) = 4;
sizeof(ptr) = 4;
So the result would be wrong.

I would do it differently and report a problem to CCS.
Gavin Pinto



Joined: 18 Oct 2009
Posts: 27
Location: Australia

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PostPosted: Mon Feb 15, 2010 10:08 pm     Reply with quote
Wayne_ wrote:
....

I would do it differently and report a problem to CCS.


well it should report 16/4 =4. Dont you think so?

sizeof(strings) = 16;
sizeof(rom char*) = 4;

My device is PIC18F8722 so the size of pointer to ROM is 4 bytes
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Wayne_



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Posts: 681

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PostPosted: Tue Feb 16, 2010 2:53 am     Reply with quote
Gavin Pinto wrote:

well it should report 16/4 =4. Dont you think so?

sizeof(strings) = 16;
sizeof(rom char*) = 4;

My device is PIC18F8722 so the size of pointer to ROM is 4 bytes


No, strings is an array of pointers containing 4 entries so if a char * pointer has a size of 2 the size of strings should be 8, the result should be 4 to match the number of entries.

edit - I just noticed your last statement. Why do you think a rom pointer for a PIC18F8722 is 4 bytes ?
Wayne_



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Posts: 681

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PostPosted: Tue Feb 16, 2010 3:05 am     Reply with quote
I have to admit, I didn't think about the device type while I was testing and have it set to 16f877a. I just tried changing it to 18f8722 but it doesn't compile.
Gavin Pinto



Joined: 18 Oct 2009
Posts: 27
Location: Australia

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PostPosted: Tue Feb 16, 2010 12:06 pm     Reply with quote
Wayne_ wrote:

edit - I just noticed your last statement. Why do you think a rom pointer for a PIC18F8722 is 4 bytes ?


I do not think it is 4 bytes. I know it is 4 bytes because the program space is 128K bytes.

The pointer size will be int32 because C does not have int24.

I prefer to say 'pointer to ROM' rather than ROM pointer.
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