Open System Services System Calls Reference Manual (G06.25+, H06.03+)

dup(2) OSS System Calls Reference Manual
NAME
dup - Duplicates an open file descriptor
LIBRARY
G-series native OSS processes: system library
H-series OSS processes: implicit libraries
SYNOPSIS
#include <unistd.h>
int dup(
int filedes);
PARAMETERS
filedes Specifies an open file descriptor obtained from a successful call to the accept(),
creat(), dup( ), dup2( ), fcntl( ), open(), pipe( ), socket(),orsocketpair() func-
tion.
DESCRIPTION
The dup( ) function returns a new file descriptor for the open file specified by the filedes parame-
ter. This file descriptor:
• Is the lowest-numbered available file descriptor
• References the same open
• Returns the same file pointer as the original file (that is, both file descriptors share one
file pointer if the object is a file)
• Returns the same access mode (read, write, or read/write)
• Returns the same file status flags (that is, both file descriptors share the same file status
flags)
• Clears the close-on-exec flag (FD_CLOEXEC bit) associated with the new file descrip-
tor so that the file remains open across calls to any function in the exec, tdm_exec, and
tdm_spawn sets of functions
NOTES
The dup( ) function provides an alternative interface to the service provided by the fcntl( ) func-
tion by using the F_DUPFD value of the request parameter. The call:
fid = dup( file1 );
is equivalent to:
fid = fcntl( file1, F_DUPFD, 0 );
RETURN VALUES
Upon successful completion, the dup( ) function returns a new file descriptor. If the dup() func-
tion fails, the value -1 is returned, and errno is set to indicate the error.
ERRORS
If any of these conditions occurs, the dup( ) function sets errno to the corresponding value:
[EBADF] The filedes parameter is not a valid open file descriptor.
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