DOKK / manpages / debian 10 / libx11-doc / XNoOp.3.en
XNoOp(3) XLIB FUNCTIONS XNoOp(3)

XNoOp - No Operation

int XNoOp(Display *display);

Specifies the connection to the X server.

The XNoOp function sends a NoOperation protocol request to the X server, thereby exercising the connection.

Xlib - C Language X Interface

libX11 1.6.7 X Version 11