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" .

Spendthrift

Answer 1

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.

Unicameral

dup and dup2 don't close the old file descriptor. – Goldofpleasure

@Chris Lutz: Thanks for pointing it out. I have corrected the error. – Unicameral

@ChrisLutz From [LDP] (tldp.org/LDP/lpg/node11.html): NOTES: the old descriptor is closed with dup2()!, please clarify. – Variorum

Answer 2

You need dup2()

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

Accost

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. – Pendley