Some programs save their data in files that end in
.asc. They probably are abbreviations for the following:
The first two at least tell whether you can expect to view the data with a text editor or not. The next two seem completely pointless to me. Why would you need to indicate that a file contains data? Or that a file was saved? Isn\'t that the point of files that you save data into them? Then the naming of input and output files seem to make sense at first. But every input file is the output of some prior process and the output file will certainly be the input of a next step, otherwise one would not need to create it in the first place.
So instead of using the above, I suggest using a suffix that contains more
meaning. Perhaps the file contains values separated by comma or tab, then
.tsv are good. Those will be associated with a default program like
a spreadsheet or my fastplot.
If the data really can only be read by your program since it is a custom binary
format, then I would use the program name as a suffix. This way no other
program will try to open those files. I sometimes see
.markdown. That is a
long file extension but it works quite nicely.