Hi,

I mistakenly wrote:
<<
*t++ means first increment the pointer, then dereference it,
otherwise this wouldn't work.
*/
while(*t++ = *s++);
}
>>

*t++ means first dereference, then increment. Since we have an
assignment both incremented pointers are not used for the assignment
of the characters.

Edward

On 01/07/2016, Edward Bartolo <edbarx@???> wrote:
> Hi,
>
> I am now studying pointers my "weakest" part of the language. The
> following is a program I wrote as an exercise to mimic what strcat
> does in a very rudimentary way. Please, be aware this is only to serve
> as an exercise and NOT to reinvent the standard functions.
>
> #include <stdio.h>
> #include <ctype.h>
>
> /* assume target string has enough free space */
> void strcat1(char* s, char *t) {
> /* find terminating null */
>
> /*
> The for loop increments pointer t after every iteration.
> Loop starts at t. The final value of t is the position of
> /0 character.
> */
> for (; *t; t++);
>
> /*
> The while loop uses C's bastardized version of an assignment
> treating it also as a statement. At each iteration, first the
> char at t is assigned the char at s. After this, both t and s
> are incremented.
>
> *t++ means first increment the pointer, then dereference it,
> otherwise this wouldn't work.
> */
> while(*t++ = *s++);
> }
>
>
> int main() {
> /*
> Here I am assuming both source and target are automatically
> appended by a \0 character. Otherwise strcat1 would go into
> an uncontrolled memory corrupting frenzy only to be stopped
> by a segmentation fault.
>
> However this didn't happen.
> */
> char source[] = "Appended end of string\n";
> char target[1024] = "Target string\n";
>
> strcat1(source, target);
> printf(target);
>
> return 0;
> }
>
> I need a memory helper to remember how things like *ch++ is evaluate
> and to read its meaning. As it is, it is definitely ambiguous as it
> can be interpreted to mean
> a) increment the pointer then dereference it
> b) dereference the pointer then increment its data.
>
> I am taking *ch++ as an expression. Some rules must exist that help
> one correctly interpret the meaning of these expressions.
>
> I know there is operator priority and rules that govern how
> expressions are evaluated. Do I need to know these at the tips of my
> fingers?
>
> Edward
>