in reply to defined vs null string

You asked about how it compares with C, so here's a C version:

#include <stdio.h>
#include <string.h>

char *undef;
char *def_empty = "";
char *def = "foo bar";

void check(char *t) {
    if (t) {
        if (strlen(t)) {
            printf("Defined loc=%p, val='%s'\n", t, t);
        }
        else {
            printf("Empty string: loc=%p\n", t);
        }
    }
    else {
        printf("Undefined (null ptr)\n");
    }
}

int main(int, char **) {
    check(undef);
    check(def_empty);
    check(def);
    return 0;
}

[download]

It gives us:

$ ./a.exe
Undefined (null ptr)
Empty string: loc=0x4020e5
Defined loc=0x4020e6, val='foo bar'

[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Replies are listed 'Best First'.
Re^2: defined vs null string
by ikegami (Patriarch) on Aug 30, 2011 at 18:54 UTC

    That would be closer to 

    sub SvPVX { unpack 'J', pack 'p', $_[0] }

if (defined $y) {
    if (length($y)) {
        printf("Defined loc=%X, val='%s'\n", SvPVX($y), $y);
    }
    else {
        printf("Empty string: loc=%X\n", SvPVX($y));
    }
}
else {
    printf("Undefined (null ptr)\n");
}

    [download]

    So you completely removed the case the OP was asking about.

    The C equivalent would be closer to the following (memory leak aside): 

    Scalar* stringify(Scalar* sv) {
   if (scalar_type(sv) == undefined) {
       fprintf(STDERR, "Use of unitialised value\n");
       return NewEmptyStringScalar();
   } else if (scalar_type(sv) == string) {
       return sv;
   } else if (scalar_type(sv) == ...) {
       ...
   } else ...
}

int eq(Scalar* sv1, Scalar* sv2) {
   return strcmp(
      stringify(sv1)->string_buffer,
      stringify(sv2)->string_buffer
          ) == 0;
}

    [download]
[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom