# readUint64

`import { readUint64 } from "destack:bytes";`

Read one unsigned 64-bit integer.

```ds title="readUint64"
export function readUint64(bytes: &'a readonly [uint8], offset: usize, order?: "bigEndian" | "littleEndian"): uint64
```

[language/library/src/bytes/bytes.ds:29:35](https://github.com/destack-sh/destack/blob/main/language/library/src/bytes/bytes.ds#L29-L35)