.\" details for dup2().
.\" 2008-10-09, mtk: add description of dup3()
.\"
-.TH DUP 2 2008-10-09 "Linux" "Linux Programmer's Manual"
+.TH DUP 2 2012-02-14 "Linux" "Linux Programmer's Manual"
.SH NAME
dup, dup2, dup3 \- duplicate a file descriptor
.SH SYNOPSIS
.BI "int dup(int " oldfd );
.BI "int dup2(int " oldfd ", int " newfd );
.sp
-.B #define _GNU_SOURCE
+.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
+.BR "#include <fcntl.h>" " /* Obtain O_* constant definitions */
.B #include <unistd.h>
.sp
.BI "int dup3(int " oldfd ", int " newfd ", int " flags );