Special variables -- $X

$X

Introduced in the 1977 ANSI M[UMPS] language standard.

Note: the value $X is an approximation of the current location of the horizontal position of the cursor on the current I/O device. There are many examples where the value of $X deviates significantly from the actual horizontal position of the cursor. This is a problem that is somewhat relieved by an addition in the 1995 standard.

> FOR I=1:1:50 WRITE I,"__" IF $X>20 WRITE !
1__2__3__4__5__6__7__
8__9__10__11__12__13__
14__15__16__17__18__19__
20__21__22__23__24__25__
26__27__28__29__30__31__
32__33__34__35__36__37__
38__39__40__

The value of $X is defined to be an approximation of the horizontal cursor coordinate, and the standard provides no guarantees about the accuracy of this approximation.

Addition in the 1995 ANSI M[UMPS] language standard.

This standard allows the value of $X to be re-defined in a SET command, so that, in case the value of $X lost synchronization with the actual value of the cursor, the programmer can correct the value of $X.

If the cursor is positioned using any of the functions from the ANSI X3.64 standard, the standard defines that the value of $X will be updated accurately.

The initial value of $X is implementation-dependent. However, if the initial value of $IO is the empty string, then the initial value of $X is 0 (zero).

This document is © Ed de Moel, 1995-2005.
It is part of a book by Ed de Moel that is published under the title "M[UMPS] by Example" (ISBN 0-918118-42-5).
Printed copies of the book are no longer available.

This document describes the various special variables that are defined in the M[UMPS] language standard (ANSI X11.1, ISO 11756).

The information in this document is NOT authoritative and subject to be modified at any moment.
Please consult the appropriate (draft) language standard for an authoritative definition.

In this document, information is included that will appear in future standards.
The MDC cannot guarantee that these 'next' standards will indeed appear.