comparing structs

[jrd]

I wish to compare two structs:

struct { ... } a;
struct { ... } b;

_bool mem_matches(void *a, void *b, int size)
{
for(;size>0;--size,++a,++b) if(*a!=*b) return false;
return true;
}

for some reason the compiler will not accept the
void * pointers. Further, if I change them to struct *'s,
the compiler hits if comparison and says field expected.
What gives? Why can't I compare structures this way?
Is it necessary to set up a union like this:

union {
struct {... } a;
char foo[sizeof(a)];
} x

?

Thank you!
Justin Dobbs
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This message was ported from CCS's old forum
Original Post ID: 1185

[jrd]

I mistyped in my post. I meant to declare the variables
const void *. Also, I fixed my syntax and it seems to work
this way. I still wish I could use (const void *) to
compare with any pointer type.

typedef struct { ... } system_t;
system_t a, b;

#define _Bool int1
_Bool memory_regions_match(system_t *a, system_t *b, _Byte n)
{
for(;n>0;--n) if(*((unsigned char*)a++)!=*((unsigned char *)b++)) return FALSE;
return TRUE;
}
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This message was ported from CCS's old forum
Original Post ID: 1186

[Tomi]

There are some problems about the things you want to implement.
The CCS C is not for scientific applications; it is for programming PIC microcontrollers. PICs use Harward architecture. Pointers to the ROM space is not allowed so you can not use a "const type *" reference (consts are stored in the ROM).
The char type is unsigned in CCS C by default so your casting "(unsigned char*)" is not necessary.
Using "void *" as a "universal pointer" is not really supported. Pointers are always passed to a function as "pointers to fundamental data" what is "char *".
This means that you can freely use in your function something like this:
a[index]
So this snippet is working fine in CCS C:

typedef struct {
char a;
float b;
int16 c;
int32 d;
} MyStructType;

char memory_regions_match(char *a, char *b, char n)
{
for(;n>0;--n) if(a[n]!=b[n]) return FALSE;
return TRUE;
}

char c1,c2;
float f1,f2;
MyStructType s1,s2;

memory_regions_match(&c1,&c2,sizeof(char));
memory_regions_match(&f1,&f2,sizeof(float));
memory_regions_match(&s1,&s2,sizeof(MyStructType));

The list:
.................... memory_regions_match(&c1,&c2,sizeof(char));
0078: MOVLW 2A // address of c1
0079: MOVWF 4A // put it into SW stack
007A: MOVLW 2B // address of c2
007B: MOVWF 4B // put it into SW stack
007C: MOVLW 01 // the char size is 1
007D: MOVWF 4C // put it into SW stack
007E: CALL 04C // call the memory_regions_match function
.................... memory_regions_match(&f1,&f2,sizeof(float));
007F: MOVLW 2C
0080: MOVWF 4A
0081: MOVLW 30
0082: MOVWF 4B
0083: MOVLW 04 // the float size is 4
0084: MOVWF 4C
0085: CALL 04C
.................... memory_regions_match(&s1,&s2,sizeof(MyStructType));
0086: MOVLW 34
0087: MOVWF 4A
0088: MOVLW 3F
0089: MOVWF 4B
008A: MOVLW 0B // the sample struct size is 11
008B: MOVWF 4C
008C: CALL 04C
___________________________
This message was ported from CCS's old forum
Original Post ID: 1197

[jrd]

:=There are some problems about the things you want to implement.

Your post was exactly what I needed. Thank you tom!
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This message was ported from CCS's old forum
Original Post ID: 1271