Re^2: Pointers and References

Hi Ken,

You're using terms — pointer, address, memory location — which I suspect you've picked up from one or more other languages. You are then attempting to apply those terms to Perl, assuming they have the same meaning. I think this may be the source of your problems.

Guilty as charged! I was trying to replicate in Perl the following program from a C tutorial on functions and pointers:

#include <stdio.h>
int sum_and_diff (int a, int b, int *res)
{
    int sum;
    sum = a + b;
    *res = a – b;
    return sum;
}
void main (void)
{
    int b = 2;
    int diff;
    printf ("The sum of 5 and %d is %d\n", b,
    sum_and_diff (5, b, &diff));
    printf ("The difference of 5 and %d is %d\n", b, diff);
}
[download]

Perhaps I just need to focus on one language at a time! And thank you for the detailed example and explanation!

You can reference and dereference to great depths if you want; as in this exaggerated example

I'm just reading this now but came to the same conclusion earlier today when I was reading some of the other responses to this thread.

I suggest you play around with examples like these to get a better understanding of how all of this works.

Agreed. What I take away from your examples is that when I try to print or output a variable that contains a reference, I can clearly see what that is in reference to. For example:

SCALAR(0x60008a730) --> reference to a scalar
ARRAY(0x60008a828)  --> reference to an array
REF(0x600003e80)    --> reference to a reference
[download]

This helps you understand how to dereference it:

$$x  # dereference reference to scalar (if $x is a scalar)
@$x  # dereference reference to array (if $x is reference to an array)
@$$x # dereference reference to reference of an array
[download]

I hope I got that last bit right!

Also note that I didn't use, or indeed need, terms such as pointer, address or memory location.

Duly noted! And thanks for the alias tip. I will have to park that one away for the time being because as useful as Perl one-liners are, I don't think I'm quite ready to use them that frequently.

Gratias tibi ago
Leudwinus

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Re^3: Pointers and References
by kcott (Archbishop) on Nov 25, 2020 at 19:51 UTC

"And thanks for the alias tip. I will have to park that one away for the time being because as useful as Perl one-liners are, I don't think I'm quite ready to use them that frequently."

I have aliases set up such that they're always available, regardless of frequency of usage. In ~/.bashrc, I have:

...
if [ -f "${HOME}/.bash_aliases" ]; then
    . "${HOME}/.bash_aliases"
fi
...
[download]

And ~/.bash_aliases has lines like this:

...
alias vi='vim'
alias view='vim -R'
...
alias perle='perl -Mstrict -Mwarnings -Mautodie=:all -MCarp::Always -E
+'
alias perlb='perl -MO=Deparse,-p -e'
...
alias apache_up='/usr/sbin/apachectl start'
alias apache_down='/usr/sbin/apachectl stop'
...
[download]

You may need to adjust to suit whatever shell you're using; however, the basic principle should be applicable to any UNIX-like system. I use this with Linux for $work; with Cygwin for personal, home use; and, up until a year or so ago, with macOS (formerly Mac OS X).

— Ken

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