Appending data to pre-exisiting files

[Richard E Maine]

On Jul 27, 2005, at 9:45 AM, Steve Edwards wrote:

> On Wed, 2005-07-27 at 16:08, Richard E Maine wrote:

>> The only standard and portable way to do this in fortran 77 is to open
>> the file and read through it to the end (backspacing after you hit the
>> end of file).  Yes, this is a pain - particularly if the file is 
>> large.
>> It is enough of a pain that it is sometimes worth doing nonstandard
>> things even though they cause porting problems.
>
> That has been my implementation using g77. I put up with the ugly code
> purely because it *does* have to be portable.

If your only problem is that the code is a bit ugly, then you are in 
pretty good shape. Ugly though it may be, it is just a few lines and 
isn't *THAT* bad. Sometimes performance can be a significant driver 
here. For example, I have applications that append entries to a log 
file. The log file can be several megabytes in size - enough to take 
noticeable time to read through. Multiple copies of the application (or 
multiple applications) sometimes share the same log file, so I can't 
just keep the file open for the entire duration of the application run 
(possibly as long as hours). Instead, I need to open and close the file 
around writing each log entry. If I used the read-to-eof approach, this 
would have me reading several megabytes for every line written. That's 
basically a non-starter in terms of performance. Normally the log files 
aren't a significant performance issue, but that's so bad that they 
become one. In f77, I was all but forced to use nonstandard constructs 
and pay the price in porting work.

That's one of the many small things that made my life easier when I 
moved to f90. The big new features get all the "press", but there were 
also a lot of small ones like that.

-- 
Richard Maine                |  Good judgment comes from experience;
Richard.Maine@nasa.gov       |  experience comes from bad judgment.
                             |        -- Mark Twain