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(g77-295.info)Large File Unit Numbers

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Large File Unit Numbers
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   If your program crashes at run time with a message including the
text `illegal unit number', that probably is a message from the
run-time library, `libg2c'.

   The message means that your program has attempted to use a file unit
number that is out of the range accepted by `libg2c'.  Normally, this
range is 0 through 99, and the high end of the range is controlled by a
`libg2c' source-file macro named `MXUNIT'.

   If you can easily change your program to use unit numbers in the
range 0 through 99, you should do so.

   Otherwise, see Note: Larger File Unit Numbers, for information on
how to change `MXUNIT' in `libg2c' so you can build and install a new
version of `libg2c' that supports the larger unit numbers you need.

   *Note:* While `libg2c' places a limit on the range of Fortran
file-unit numbers, the underlying library and operating system might
impose different kinds of limits.  For example, some systems limit the
number of files simultaneously open by a running program.  Information
on how to increase these limits should be found in your system's
documentation.