Re: Reading a line of arbitrary length

[Rex Reges <reges@mds.lmco.com>]

Thomas Koenig wrote:
> 
> What's the best way of reading a line of arbitrary length in Ada?
> 
> Get_Line only works on Strings, not Unbounded_Strings.  Would I need
> to read in chunks of fixed length, then paste them together?
> --
> 74 a3 53 cc 0b 19

Inevitably, you will get various unexpected problems using 
the Get_Line function.  Let's assume that you create a 
very large string buffer to handle most situations:

   Input_Buffer : String( 1..10_000_000 ) ;

You may run into one of the following problems:

   1) The IO buffer allocated by the operating system for
      file IO is too small to handle large strings and you
      will get an exception (happens on the Vax for strings
      on the order of a million characters).

   2) You will get a storage_error exception because the 
      variable Input_Buffer will exceed the operating system
      limits on your program size (or more commonly that you 
      don't have stack space to instantiate it).

   3) An exception will occur during the processing and all the
      data for that line will be lost.  The most common exception
      is when an end-of-file is found before the end-of-line 
      (a favorite of xedit users).

Unfortunately, it turns out that getting one character at a time
is the best solution to avoid losing data and to handle unlimited
length strings.  Actully, this is not as bad as it seems since
the machines I have used buffer I/O in chunks anyway so that a
get does not involve a disk access most of the time.


-- 
Rex Reges                      or you can call me The Fixer 
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