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addresses of a string's elements

 
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rikotech8



Joined: 10 Dec 2011
Posts: 376
Location: Sofiq,Bulgariq

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addresses of a string's elements
PostPosted: Sun Nov 18, 2012 6:27 am     Reply with quote
Hi! How can I know what is the address of each element of string.
For example:
Code:

const char str[]={1,2,3,4};

So, what is the address of str[0],str[1]....ect?
I tried with &str but I get garbage.
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Sun Nov 18, 2012 6:47 am     Reply with quote
With a normal string.

str, _is_ the address of the first element.
str+1 the address of the second, etc. etc.....

However this will not work with const strings. You have to get your head round the fact that in the PIC, there are two separate memory spaces. So there are two sddress 0's, etc... One in the ROM, and one in RAM.

If you change your declaration to:
Code:

rom char str[]={1,2,3,4};


This tells the compiler to use a (more bulky) way of storing the const strings, and construct 'virtual' pointers to these.

In the original 'const' form:

addressof(str);

will return the ROM address where str is stored, _but_ you then need to access this with the 'read_program_memory' function, not using *. (* handles accessing RAM, not ROM).

&str, would always be garbage in any version, since it will give the address of the variable 'str', not it's contents.....

Best Wishes
rikotech8



Joined: 10 Dec 2011
Posts: 376
Location: Sofiq,Bulgariq

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PostPosted: Sun Nov 18, 2012 8:52 am     Reply with quote
You are saying that declaring constant variable doesn't take RAM but ROM. I tried with new declaration

Code:
char str[]={1,12,2};


and then I succeed to read the address of str by using '&', so thank you, I see now. I don't know if you understand me. Excuse my bad englisnh!
Ttelmah



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PostPosted: Sun Nov 18, 2012 10:21 am     Reply with quote
Yes, you have it.

Remember also, you don't need '&'. In C, the name of an array, is it's address. So:

str, is exactly the same as &str[0]

This is a standard C 'shortcut'.

Best Wishes
rikotech8



Joined: 10 Dec 2011
Posts: 376
Location: Sofiq,Bulgariq

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PostPosted: Mon Nov 19, 2012 12:50 pm     Reply with quote
Mhm.. I didn't know that. Thank you again!
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