How to actually close a write-stream

Question

I don't know too much about writing and reading to and from files. But I managed to create a nice command for me where I need to write something into a text-file and later-on read it again.

\newcommand{\customwrite}[1]{
  \newwrite\tempfile%
  \immediate\openout\tempfile=filename_#1.txt%
  \immediate\write\tempfile{\the\figheight}%
  \immediate\closeout\tempfile%
}

The reading is achieved by

\newcommand{\customread}[1]{
  \newread\tempfile%
  \openin\tempfile=filename_#1.txt%
  \read\tempfile to \fileline%
  \setlength\figheightex\fileline%
  \closein\tempfile%
}

Both things works fine for me as long as I have not too much of this calls. Recently, I had a bigger document and everything failed and I got the message No room for a new \write. I searched for this error and what I found is, Latex is only capable of opening 16 write and 16 read streams. Apparently \closeout and \closein don't actually close these streams what I thought.

My question is now: is it somehow possible to actually close these streams?

Answer 1

You reserve a new read/write slot every time you read or write, but you don't need it. Moving \new... out of the definitions does the trick:

\newwrite\mytempout
\newcommand{\customwrite}[1]{%
  \immediate\openout\mytempout=filename_#1.txt %
  \immediate\write\mytempout{\the\figheight}%
  \immediate\closeout\mytempout
}

\newread\mytempin
\newcommand{\customread}[1]{%
  \openin\mytempin=filename_#1.txt %
  \read\mytempin to \fileline
  \setlength\figheightex\fileline
  \closein\mytempin
}

I added and removed some of the %s to make it more reasonable, see e.g. Where are the necessary places to be appended with % to remove unwanted spaces?