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Pointer to const array?

 
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Guest
Pointer to const array?
PostPosted: Mon Apr 21, 2008 4:41 am     Reply with quote
Hi

What is wrong here. The code is just an ex. from a bigger context.

Is I handling the pointer corect?

The problm is I cant accecc the const array?

Code:
//located in prom
const int8 c_data[6]={0xFF,0x41,0x61,0x11,0x91,0xd1};

//test function
void t2(void){
 int8* data;
 int16 i;
 data=&c_data;
 for(i=0;i<6;i++) write_data(*data++);
}




But if I use this function - no problem!
Code:
void t3{
 int16 i;
 for(i=0;i<6;i++) write_data(c_data[i]);
}
Matro
Guest
PostPosted: Mon Apr 21, 2008 5:02 am     Reply with quote
Below an excerpt of CCS help about constant data tables :
Quote:

BYTE CONST TABLE [10]= {9,8,7,6,5,4,3,2,1,0};

and to access the table use:
x = TABLE [i];
OR
x = TABLE [5];

BUT NOT
ptr = &TABLE [i];

In this case, a pointer to the table cannot be constructed.

I think all is here...

Matro
Guest
PostPosted: Mon Apr 21, 2008 5:13 am     Reply with quote
Hi

Yes I have looked at this ex. but, is it impossible???

/F
Ttelmah
Guest
PostPosted: Mon Apr 21, 2008 5:22 am     Reply with quote
Actually, you can now (only working in the last few compiler versions), have pointers to constant arrays, _but_ you have to use the 'ROM' construct, rather than the 'const' construct. The difference is that the latter includes a header 'program', to access the data. The former just places the data, and has a slightly more complex access arrangement. This allows the code to be able to calculate 'where' the actual data is, and pointers to be used.
So:
Code:

//located in prom
int8 ROM c_data[6]={0xFF,0x41,0x61,0x11,0x91,0xd1};

//test function
void t2(void){
 int8* data;
 int16 i;
 data=&c_data;
 for(i=0;i<6;i++)
    write_data(*data++);
}

Should work.

The manual has not 'caught up' with this, but it is in the 'readme.txt' that comes with the compiler.

Best Wishes
Guest
PostPosted: Mon Apr 21, 2008 6:40 am     Reply with quote
Hi

Thanks, but I cant get it to work using pointers?

I just use the old way...
Ttelmah
Guest
PostPosted: Mon Apr 21, 2008 7:02 am     Reply with quote
What I posted, compiled, and ran, on 4.070, using putc, instead of write_data, and gave the right output.

Best Wishes
Guest
PostPosted: Mon Apr 21, 2008 8:00 am     Reply with quote
Hi.

Thanks for the information:-)
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