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Top Forums UNIX for Dummies Questions & Answers Difference between file descriptor and file pointer Post 302402935 by jimmyuk on Thursday 11th of March 2010 01:56:12 AM
Old 03-11-2010
Difference between file descriptor and file pointer

hi....,
can anyone tell me what is the exact difference between file descriptor and file pointer...... and why file descriptor takes integer value???Smilie
 

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dup(2)								   System Calls 							    dup(2)

NAME
dup - duplicate an open file descriptor SYNOPSIS
#include <unistd.h> int dup(int fildes); DESCRIPTION
The dup() function returns a new file descriptor having the following in common with the original open file descriptor fildes: o same open file (or pipe) o same file pointer (that is, both file descriptors share one file pointer) o same access mode (read, write or read/write). The new file descriptor is set to remain open across exec functions (see fcntl(2)). The file descriptor returned is the lowest one available. The dup(fildes) function call is equivalent to: fcntl(fildes, F_DUPFD, 0) RETURN VALUES
Upon successful completion, a non-negative integer representing the file descriptor is returned. Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The dup() function will fail if: EBADF The fildes argument is not a valid open file descriptor. EINTR A signal was caught during the execution of the dup() function. EMFILE The process has too many open files (see getrlimit(2)). ENOLINK The fildes argument is on a remote machine and the link to that machine is no longer active. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ SEE ALSO
close(2), creat(2), exec(2), fcntl(2), getrlimit(2), open(2), pipe(2), dup2(3C), lockf(3C), attributes(5), standards(5) SunOS 5.10 28 Dec 1996 dup(2)
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