# libtmux::exactly_one

- **Module:** libtmux
- **Package:** libtmux-cxx
- **Language:** C++
- **Kind:** function
- **Source:** https://github.com/libtmux/libtmux-cxx/blob/85e8bd603a322dc32bb8b9aeb1a72bcf36945f1d/include/libtmux/cardinality.hpp#L61
- **Page:** https://libtmux.org/reference/cxx/libtmux-exactly_one/

```
libtmux::exactly_one(Range: ReferenceRange, range: Range &) -> ReferenceRange
```

`exactly_one` states that several is a caller error, and says which one.