# Can't get last pair in FDBKeyValue array

**URL:** <https://forums.foundationdb.org/t/cant-get-last-pair-in-fdbkeyvalue-array/1252>\
**Category:** Using FoundationDB\
**Created:** [March 24, 2019, 6:57am UTC](https://forums.foundationdb.org/t/cant-get-last-pair-in-fdbkeyvalue-array/1252 "2019-03-24T06:57:23Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![jonahwest](https://avatars.discourse-cdn.com/v4/letter/j/90db22/32.png) [@jonahwest](https://forums.foundationdb.org/u/jonahwest)\
**Post date:** [March 24, 2019, 6:57am UTC](https://forums.foundationdb.org/t/cant-get-last-pair-in-fdbkeyvalue-array/1252/1 "2019-03-24T06:57:23Z")

</div>

I’ve been using range reads in the FoundationDB C API with the following code:

```
FDBFuture *future = fdb_transaction_get_range(tr, beginKey, beginKeySize, 0, 0,
endKey, endKeySize, 0, 0, limit, 0, FDB_STREAMING_MODE_WANT_ALL, 0, 0, 0);
//Wait for future and check errors...
int outMore, outCount;
FDBKeyValue *keyValue = fdb_future_get_keyvalue_array(future, &keyValue, &outCount, &outMore);
printf("%d\n", outCount);
printf("%.*s\n", keyValue[0].key_length, keyValue[0].key);
printf("%.*s\n", keyValue[1].key_length, keyValue[1].key);
printf("%.*s\n", keyValue[2].key_length, keyValue[2].key);
printf("%.*s\n", keyValue[3].key_length, keyValue[3].key);

```

When I run `getrange '' \xff`, I get:

```
`hello' is `world'
`hi' is `everyone'
`mykey` is `myvalue'

```

However, the output of my C program is:

```
3

hello
hi

```

The first pair (`keyValue[0]`) is empty. The next pairs are present, however I would expect `hello` to be at position 0, and `hi` to be at position 1. When reading `keyValue[3]`, nothing is present, as expected.

I have a few questions:

1. How can I get all 3 pairs?
2. Why is `keyValue[0]` empty?

I would appreciate any help. Thanks!

---

<div class="post-metadata">

**Author:** ![ajbeamon](https://sea1.discourse-cdn.com/foundationdb/user_avatar/forums.foundationdb.org/ajbeamon/32/13_2.png) [@ajbeamon](https://forums.foundationdb.org/u/ajbeamon)\
**Post date:** [March 24, 2019, 1:49pm UTC](https://forums.foundationdb.org/t/cant-get-last-pair-in-fdbkeyvalue-array/1252/2 "2019-03-24T13:49:30Z")

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I think you’re running into two separate issues here. First, `fdbcli` uses double quotes to quote strings rather than single quotes. Your current `fdbcli` command will not return any key that comes lexicographically before the string `"''"`, and my guess is that one such key exists. Try running `getrange "" \xff` instead to see what’s there.

The second thing is that the end key selector in a get range call is exclusive. The call will resolve the key selector first and then exclude whatever key is resolved. Assuming your end key is `"\xff"`, an `offset` of 0 and an `or_equal` of 0 will resolve to the last key in the database before your end key, and that key will be excluded from your result (i.e. this is equivalent to [`LAST_LESS_THAN`](https://apple.github.io/foundationdb/api-c.html#key-selectors)). Instead, you should use `FIRST_GREATER_OR_EQUAL` to resolve to the first key outside of your desired range (or without the macro, this is `offset=1`, `or_equal=0`).

---

<div class="post-metadata">

**Author:** ![jonahwest](https://avatars.discourse-cdn.com/v4/letter/j/90db22/32.png) [@jonahwest](https://forums.foundationdb.org/u/jonahwest)\
**Post date:** [March 25, 2019, 9:13pm UTC](https://forums.foundationdb.org/t/cant-get-last-pair-in-fdbkeyvalue-array/1252/3 "2019-03-25T21:13:21Z")

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@ajbeamon Thanks, that worked! However, I seem to randomly get error code `2012: Range limits not valid`. What could be causing this?

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<div class="post-metadata">

**Author:** ![ajbeamon](https://sea1.discourse-cdn.com/foundationdb/user_avatar/forums.foundationdb.org/ajbeamon/32/13_2.png) [@ajbeamon](https://forums.foundationdb.org/u/ajbeamon)\
**Post date:** [March 25, 2019, 9:41pm UTC](https://forums.foundationdb.org/t/cant-get-last-pair-in-fdbkeyvalue-array/1252/4 "2019-03-25T21:41:12Z")

</div>

This isn’t an error I’ve really seen much of, but based on my interpretation of the code, it looks like it could happen if you pass in a negative row or byte limit. Is that happening in your case?

If not, what are your arguments to the `fdb_transaction_get_range` call?

---

<div class="post-metadata">

**Author:** ![jonahwest](https://avatars.discourse-cdn.com/v4/letter/j/90db22/32.png) [@jonahwest](https://forums.foundationdb.org/u/jonahwest)\
**Post date:** [March 25, 2019, 9:53pm UTC](https://forums.foundationdb.org/t/cant-get-last-pair-in-fdbkeyvalue-array/1252/5 "2019-03-25T21:53:28Z")

</div>

EDIT: Problem solved! It was my fault. I forgot to dereference a pointer that I was passing to `fdb_transaction_get_range()`.

I’m not using a byte limit, and `limit` is always set to 5. It seems that I get the error on `fdb_future_get_error()`, and it will occur seemingly randomly even when the contents of the database has not changed.

```
FDBFuture *future = fdb_transaction_get_range(tr, FDB_KEYSEL_FIRST_GREATER_THAN(
"r\x00", 2), FDB_KEYSEL_FIRST_GREATER_OR_EQUAL(string, size), 5, 0,
FDB_STREAMING_MODE_WANT_ALL, 0, 0, 1);
```