On Feb 21, 12:37*pm, Michael Mair <Michael.M...@invalid.invalid>
wrote:
> Mahesh wrote:
> > #include <stdio.h>
> > #include <string.h>
> > #include <malloc.h>
>
> Not a standard C header; use <stdlib.h> for malloc(), realloc(),
> free().
>
> > int main(void)
> > {
> > * * int key = 120;
> > * * char *s = "String to Encrypt using XOR";
> > * * char *ss = s;
> > * * char echar;
> > * * char dchar;
> > * * size_t sizeofmsg = strlen(s)*sizeof(char*);
>
> Wrong calculation.
> It should be (number of elements)*(size of the type s points to).
> That is,
> * sizeofmsg = (strlen(s) + 1) * sizeof *s;
> as s points to char and sizeof (char) is guaranteed to be 1,
> you can write
> * sizeofmsg = strlen(s) + 1;
> The "+1" stems from the string terminator that is not included
> in the string length but contributes to the string's size.
>
>
>
> > * * char *emsg = (char*)malloc(sizeofmsg);
> > * * char *dmsg = (char*)malloc(sizeofmsg);
>
> Note that the cast is unnecessary and can hide an error; around
> here,
> * T *p = malloc(NumberOfElems * sizeof *p);
> is recommended.
>
> > * * char *ddmsg = dmsg;
> > * * char *eemsg = emsg;
> > * * int lenofmsg = strlen(s);
> > * * int count=0;
> > * * int i=0;
>
> > * * while(count++<strlen(s)){
>
> > * * * * echar = (char)(*ss^key);
>
> Note that XOR encryption of the value key leads to 0 ('\0'),
> which also is the string terminator.
>
> > * * * * emsg = &echar;
>
> You probably mean
> * *emsg = echar;
>
> &echar is just that, the address of echar; you do not change
> the contents of the storage area you got from malloc().
> So, in every iteration, you point emsg at the same object.
>
> Note that for s, you iterate on the copy, and for emsg, you
> iterate on the "original". This can lead to problems.
>
> > * * * * emsg++;
> > * * * * ss++;
> > * * }
> > * * count=0;
> > * * emsg = eemsg; *// HERE when i restore the address of emsg via
> > eemsg, i'm not able to
> > * * * * * * * * * * * * * * // decrypt. How to restore the address of
> > original pointer to char ?.
>
> // style comments break easily on usenet; I recommend that you use
> /**/ comments which cannot change semantics or "compilability" due
> to line breaks
>
> > * * i=0;
> > * * printf("\n");
> > * * while(count++<strlen(s)){
>
> > * * * * echar = *emsg;
> > * * * * dchar = (char)(echar ^ key);
> > * * * * ddmsg = &dchar;
> > * * * * printf(" %c",dchar);
> > * * * * emsg++;
> > * * * * ddmsg++;
> > * * }
> > * * printf("\n");
> > * * getch();
> > * * return 0;
> > }
>
> Cheers
> * Michael
> --
> E-Mail: Mine is an * /at/ gmx /dot/ de * address.
Thanks you so much Michael for you invaluable reply.
-
Mahesh
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