pointer string

cimon's Avatar, Join Date: Feb 2007
Go4Expert Member
Hello

If I take a string declaration as below:

char str[5]="Mike";
than the following statement does NOT produce error
str[start] ^= str[end];

If I take a string declaration as below:
char *str="Mike";
that the above mentioned statement str[start] ^= str[end]; DOES produce error.

So I want to know , that if my string declaration is as in second case (char *str="Mike" than , how to write XOR statement so that it should not produce error.

Thank You
0
oogabooga's Avatar
Ambitious contributor
The second case is a pointer to a string CONSTANT.
So you cannot (generally) change it.
0
cimon's Avatar, Join Date: Feb 2007
Go4Expert Member
Thank you
0
micsom's Avatar, Join Date: Oct 2008
Go4Expert Member
buddy i tried out ur code
char *str="MIKE";
str[0]^=str[4];
printf(" %s",str);

it gives no error... so i dont get it were is ur problem?
0
xpi0t0s's Avatar, Join Date: Aug 2004
Mentor
micsom, you're probably using a different compiler, which one is it? Modifying a string constant should throw an error, since it's an operation you shouldn't perform.

XOR-ing something with zero DOESN'T modify it, so mabye the compiler's outsmarting the lot of us. Try this:
Code:
char *str1="Mike";
char *str2=str1;
xtr1[0]^=str[3];
printf("%s\n",str2);
0
back from retirement's Avatar, Join Date: Nov 2008
Contributor
Quote:
Originally Posted by xpi0t0s
Try this:
Code:
char *str1="Mike";
char *str2=str1;
xtr1[0]^=str[3];
printf("%s\n",str2);
I have tried it in my pc....I modified it a bit....and it is running without error....

my code is...
Code:
#include<stdio.h>
#include<conio.h>

void main()
{
char *str1="Mike";
char *str2=str1;
str1[0]^=str1[4];
printf("%s\n",str2);
getch();
}
Is there anything wrong in my understanding??
0
back from retirement's Avatar, Join Date: Nov 2008
Contributor
Actually i first tried with th given code for which the output was:
Code:
(ike
I don't know why....

But then when I changed str1[3] to str1[4], the problem got solved immediately....cna anyone explain me why??
0
xpi0t0s's Avatar, Join Date: Aug 2004
Mentor
Well as I said you shouldn't modify string constants so str1[<anything>]^=<anthing> should throw an error - a compile time error if nothing else.
However if it works, to find out why 'M' xor 'e' produces '(' you'll need to look at an ASCII table and the binary values of those three characters.
'M' xor str1[4] = 'M', since str1[4]=0 (it's the terminating NULL). And as I said above, xor-ing anything with zero has no effect.
0
back from retirement's Avatar, Join Date: Nov 2008
Contributor
Thanks......now I hope I understand the lot....thank you very very much xpi0tos