Truncate a file

[Jawade]

Is there a way to truncate a file? Like this:

Open "Myfile" For Binary As #1
LOF(1) = &h2000
Close #1

[grindstone]

It's a little more complicated, but still quite easy:

Dim As String filename = "myfile"
Dim As String tempfile = "temp"

Open filename For Binary As #1
Open tempfile For Output As #2
Print #2, Input(1024, #1);
Close
Kill filename
Name(tempfile, filename)

Alternatively, if the file isn't too big, you can use a string as buffer:

Code: Select all

Dim As String filename = "myfile"
Dim As String buffer

Open filename For Binary As #1
buffer = Input(1024, #1)
Close #1
Open filename For Output As #1
Print #1, buffer;
Close #1

[fxm]

Yes, or as an alternative, replace the temporary file with a temporary string:

Code: Select all

Dim As String filename = "myfile"
Dim As String s

Open filename For Binary Access Read As #1
s = Input(1024, #1)
Close #1
Open filename For Output As #1
Print #1, s;
s = ""
Close #1

[/s]

[edit]
Post cancelled due to code duplication with the above alternative.

[Jawade]

Yes, I did it on that way, with a temp file or a temp string.
I hoped there was a way to do it with 1 move.

Thanks.

[St_W]

There's such a function in the CRT, which you can use (and is included in every FB binary anyway, so doesn't cause any bloat or additional dependencies). See ftruncate (or chsize on windows).
See also https://freebasic.net/forum/viewtopic.p ... 27&p=47265

[Jawade]

Very interesting, I go at work with it.

[dodicat]

To keep truncicated file data,looks like you should use "a" -- append.

Code: Select all

#include "file.bi"
#include "crt.bi"

Sub save(filename As String,text As String)
    Var f=fopen(filename,"w")
    fprintf(f,"%s",text)
    fclose(f)
End Sub

Sub truncicate(filename As String,l As Long)
    Var f=fopen(filename,"a") '<--------- append
    Var handle=_fileno( f )
    _chsize(handle,l)
    fclose(f)
End Sub

Dim As String f="abcdefghijklmnopqrstuvwxyz"
f+=Ucase(f)+Chr(13,10)
f+=f
f+=f
f=rtrim(f,Chr(13,10))'take off chr(13,10)
'===========
save("test",f)
Print Filelen("test")
Shell "type test"
Print
truncicate("test",58)
Print Filelen("test")
Shell "type test"
Print
truncicate("test",5)
Print Filelen("test")
Shell "type test"
print
Sleep  

[Jawade]

It's very nice. Thanks.