If you want to return a list of values (suffixes) that you can assign in a statement like

my @a = Suff(@string);
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you'd need to return them on the stack (Perl's stack, not C's). For this, there are the Inline macros

Inline_Stack_Vars
Inline_Stack_Reset
Inline_Stack_Push(sv)
Inline_Stack_Done
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which should be used in that sequence (of course, push as many values as you need).

As an alternative, you could create (and fill) an array (AV) on the XS side, and return a reference to it. This means, you'd assign it like this

my $aref = Suff(@string);
# print "@$aref";  # or whatever
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Other than that, it's hard to help (well, for me at least), because from your sample code I can't really make any inferences as to what exactly you're trying to do.

Update: (in response to your update)

#!/usr/bin/perl -wl
use strict;
use Inline C => <<'END_C';

void test() {
    Inline_Stack_Vars;
    Inline_Stack_Reset;

    char *string = "lhfsadgfbfsdaubsdkj";
    int i;
    STRLEN n = strlen(string);
    for(i=0; i<n; i++){
        Inline_Stack_Push( sv_2mortal( newSVpv(string + i, 0) ) );
    }
    Inline_Stack_Done;
}
END_C

my @a = test();
print for @a;
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Output:

lhfsadgfbfsdaubsdkj
hfsadgfbfsdaubsdkj
fsadgfbfsdaubsdkj
sadgfbfsdaubsdkj
adgfbfsdaubsdkj
dgfbfsdaubsdkj
gfbfsdaubsdkj
fbfsdaubsdkj
bfsdaubsdkj
fsdaubsdkj
sdaubsdkj
daubsdkj
aubsdkj
ubsdkj
bsdkj
sdkj
dkj
kj
j
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