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content of a specific location in a string

 
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hadeelqasaimeh



Joined: 05 Jan 2006
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content of a specific location in a string
PostPosted: Sat Jun 17, 2006 2:29 am     Reply with quote

hi all
i need to know a content of a specific location in some string i have recieved from rs-232 port.
for example i need to know whats in S[10] in location 10,,so how to do?

thanx
Ttelmah
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PostPosted: Sat Jun 17, 2006 3:09 am     Reply with quote

In C, there is a 'cross correlation', between what are called 'pointers', and 'arrays'. If (for instance), you have:

char str[20];

//and then call:

gets(str);

//which sends the 'pointer' to 'str', to the function, then after the data is retrieved:

str[0] will contain the first character received.

So, 'strings', are just arrays of characters (with a '0' in the last location used), and can be accessed either way at will. Using the 'pointer' notation:

*(str+10)

will be the 'contents' of the _eleventh_ character in the string. Remember that throughout C, things arrays, pointers etc., are 'zero referenced', so a ten element string (str[10]), has elements str[0] to str[9]. Also that for a string, there must be a terminating '0', so only nine useable characters can actually be held in such a ten element array.
Forgetting that you need this 'extra' character, and the use of the zero location, are the two commonest problems with strings in C.

Best Wishes
garage
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PostPosted: Sat Jun 17, 2006 11:41 pm     Reply with quote

please if you have a simple example code of this!!
thank you
hadeelqasaimeh



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PostPosted: Sat Jun 17, 2006 11:42 pm     Reply with quote

thanx
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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Re: content of a specific location in a string
PostPosted: Sun Jun 18, 2006 9:00 pm     Reply with quote

hadeelqasaimeh wrote:
hi all
i need to know a content of a specific location in some string i have recieved from rs-232 port.
for example i need to know whats in S[10] in location 10,,so how to do?

thanx


The 10th character in a string is s[9].
hadeelqasaimeh



Joined: 05 Jan 2006
Posts: 105

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so....
PostPosted: Mon Jun 19, 2006 12:08 am     Reply with quote

hi
i understand that
Quote:
so a ten element string (str[10]), has elements str[0] to str[9].

from first reply

now mark said
Quote:
The 10th character in a string is s[9].


i think this different!!!!so what to do guyes? Shocked
if there is some example
asmallri



Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia

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PostPosted: Mon Jun 19, 2006 12:31 am     Reply with quote

assuming the following:
Code:

        char Mesg[20];
   sprintf(Mesg, "Hello, world");



the line
Code:

      printf("%c", Mesg[5])

will print the , character

the line
Code:

       printf("%s", &Mesg[3]);

will print the message
lo, world

Corrected - thanks Mark for spotting that deliberate error to test who was awake :-)
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Last edited by asmallri on Mon Jun 19, 2006 6:43 pm; edited 1 time in total
Mark



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Posts: 2838
Location: Atlanta, GA

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PostPosted: Mon Jun 19, 2006 7:53 am     Reply with quote

asmallri wrote:
assuming the following:
Code:

        char Mesg[20];
   sprintf(Mesg, "Hello, world");



the line
Code:

      printf("%c", *Mesg[5])

will print the , character

the line
Code:

       printf("%s", &Mesg[3]);

will print the message
lo, world


I think you meant to write

Code:

      printf("%c", Mesg[5])
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