Append a string to the beginning of a file

Question

Question

Gevorg Arutiunian · Jun 13, 2017

#Object Data Model #Caché

How do I append a string to the beginning of a %FileCharacterStream in an existing file?

Discussion (5)1

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Vitaliy Serdtsev · Jun 14, 2017

E.g.:

s fileName="C:\temp\test.txt"
s f=##class(%FileCharacterStream).%New()
s f.Filename=fileName
s f1=##class(%FileCharacterStream).%New()
s f1.Filename=fileName
   
d f.Write("start ")
d f.CopyFrom(f1)
d f.Write(" end")

d f.SaveStream()
s f="",f1=""

Result:

test.txt (Before): bla-bla-bla
test.txt (After): start bla-bla-bla end

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John Murray · Jun 14, 2017

Gevorg, you can give Vitaliy credit for the answer by clicking the checkmark alongside the answer header:

This will also mark your question as "answered".

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score 0 · Answer 1 · 2017-06-14T06:58:26-04:00

Gevorg Arutiunian · Jun 14, 2017

Thank!

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score 0 · Answer 2 · 2017-06-14T14:11:30-04:00

That's what I though, but it seemed slow.

Isn't there anyway to move the stream cursor back without erasing the existing data?
And if not, couldn't that be done using a device directly?

score 0 · Answer 3 · 2017-06-14T15:23:01-04:00

Not possible, due to data in the file stored sequentially. If you want to insert some data in any place, it means you should move all next data on the disk too. So, the only way it is a new file.