# MX\_SETEXT

> [HTML Version](mx_setext.htm)

_Reviewed and revised April 2024_

**xcall MIAMEX, MX\_SETEXT, ext**

MX\_SETEXT (MIAMEX 32) may be used to set the default file extension for a subsequent file open operation.

**Parameters**

_ext_  ([String](string.md))  \[in\]

up to four bytes long, specifying the desired default extension such as "DAT", "xlsx", etc.