Create a file descriptor

Question

I want to create a file descriptor in C whose value i will specify in code. I have a integer variable which specifies the value of file descriptor to be created. For example i may need a file descriptor whose value is 5 and later associate that with the file named "sample.dat" .

phoxis · Answer 1 · 2011-05-09T11:37:08.907

6

fd = open ("sample.dat", O_RDONLY); open the file

dup2 (fd, 5); and copy the file descriptor fd into the descriptor number 5

now you can do read (5, buffer, BUFF_MAX); or also use fd to access the same file. You need to close the fd explicitly if you do not need it.

As @Arkadiy told see man dup2 for details.

edited May 09 '11 at 11:37

answered May 09 '11 at 11:18

phoxis

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`dup` and `dup2` don't close the old file descriptor. – Chris Lutz May 09 '11 at 11:22
@Chris Lutz: Thanks for pointing it out. I have corrected the error. – phoxis May 09 '11 at 11:37
@ChrisLutz From [LDP] (https://www.tldp.org/LDP/lpg/node11.html): `NOTES: the old descriptor is closed with dup2()!`, please clarify. – fde-capu May 07 '20 at 10:40

score 4 · Answer 2 · answered May 09 '11 at 10:58

4

You need dup2()

http://linux.die.net/man/2/dup

answered May 09 '11 at 10:58

1

You have to be careful. If `newfd` already belongs to a file it is closed! I think you would be better of using something like a map. – RedX May 09 '11 at 11:14

Create a file descriptor

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