dup2() duplicate open file descriptor onto another file descriptor	Function
	SYNOPSIS DESCRIPTION PARAMETERS RETURN VALUES CONFORMANCE MULTITHREAD SAFETY LEVEL PORTING ISSUES AVAILABILITY SEE ALSO

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SYNOPSIS

#include <unistd.h>

int dup(int fildes, int fildes2);

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DESCRIPTION

The dup2() function duplicates an open file descriptor. Specifically, it provides an alternate interface to the service provided by the fcntl() function using the F_DUPFD constant command value, with fildes2 for its third argument. The duplicated file descriptor shares any locks with the original.

On success, dup2() returns a new file descriptor that has the following in common with the original:

• Same open file (or pipe)
• Same file pointer (both file descriptors share one file pointer)
• Same access mode (read, write, or read/write)

The new file descriptor is set to remain open across exec() functions.

The call:

fid = dup2(fildes, fildes2);

is equivalent to:

close(fildes2);
fid = fcntl(fildes, F_DUPFD, fildes2);

with the following exceptions:

• If fildes2 is negative or greater than or equal to OPEN_MAX, the dup2() function returns a value of -1 and sets errno to EBADF.
• If fildes is a valid file descriptor and is equal to fildes2, the dup2() function returns fildes2 without closing it.
• If fildes is not a valid file descriptor, dup2() fails and does not close fildes2.
• If successful, dup2() returns a value that is equal to the value of fildes2. If a failure occurs, it returns a value of -1.

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PARAMETERS

fildes 

Is the file descriptor to duplicate.

fildes2 

Is the file descriptor that fildes is duplicated onto.

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RETURN VALUES

If successful, dup2() returns a nonnegative integer; namely, the duplicated file descriptor, which is the lowest available descriptor. If failed, it returns a -1 and sets errno to the corresponding value.

EBADF 

fildes is not a valid open file descriptor.

EINTR 

A signal was caught during the dup2() system call.

EMFILE 

The number of file descriptors exceeds OPEN_MAX.

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CONFORMANCE

POSIX.1 (1996)

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MULTITHREAD SAFETY LEVEL

Async-signal-safe.

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PORTING ISSUES

None.

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AVAILABILITY

PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Professional Developers 64-Bit Edition
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition

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SEE ALSO

Functions:

close(), creat(), dup(), execl(), execle(), execlp(), execlpe(), execv(), execve(), execvp(), execvpe(), fcntl(), lockf(), open(), pipe(), socket()

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PTC MKS Toolkit 10.5 Documentation Build 40.