#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;
}

##</code><code>##

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