2

I'm looking for a solution to the following problem:

\def\m#1{{
   \dimen0=200pt
   \#1=\the#1 % Outputs 200pt rather than 100pt
}}

\dimen0=100pt
\m{\dimen0}

EDIT:

The code sample above illustrates that passing a register as an argument to a macro could lead to surprising results if the macro happens to use the same register internally. So I wonder if there is a way to pass the value of a register rather than the register itself.

Improve this question
7
  • \m{\dimen0} sets \dimen0=200pt so it overrides the \dimen0=100pt you wrote before.
    – Manuel
    Oct 17, 2014 at 12:46
  • 1
    I think you will need to specify what you are actually trying to achieve: perhaps you want to pass the value of a register as the argument?
    – Joseph Wright ♦
    Oct 17, 2014 at 12:47
  • @JosephWright Yes, I want to pass the value of a register as an argument to a macro, not the register itself.
    – SJU
    Oct 17, 2014 at 12:57
  • @AngelTsankov OK, could you specify if the argument will always be a register (say either \dimen<number> or \mydimen), or could be a literal, macro, ... as well
    – Joseph Wright ♦
    Oct 17, 2014 at 12:59
  • @JosephWright The problem illustrated in the code sample above is that of passing a "scratchwork" register as an argument to a macro: the macro could use the same register, e.g. for internal calculations.
    – SJU
    Oct 17, 2014 at 13:11

2 Answers 2

Reset to default
2

You can put expanded value of the register to the macro \m. No matter if eTeX is used or isn't, because we needn't to use \dimexpr.

\def\m#1{{
   \dimen0=200pt
   \#1=#1 % Outputs 200pt rather than 100pt
}}

\dimen0=100pt
\expandafter\m\expandafter{\the\dimen0}
Improve this answer
1

If you use e-TeX, you can avoid using a register, exploiting the fact that \dimexpr is essentially a nameless dimension register:

\def\m#1{\expandafter\minner\expandafter{\the\dimexpr#1\relax}}
\def\minner#1{{\dimen0=200pt \#1=#1}}

The input \dimen0=100pt \m{\dimen0} will produce

#1=100.0pt

Without e-TeX and \dimexpr, the workaround is to reserve a register for this particular purpose:

\newdimen\mypersonalandprivateregister
\def\m#1{\mypersonalandprivateregister=#1\relax
  {{\dimen0=200pt \#1=\the\mypersonalandprivateregister}}%
}

Of course, the body of \m mustn't contain any other assignment to \mypersonalandprivateregister.

Improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .