I keep forgetting this, so although it is a note to self, I post it here too. The easiest way to find out what symbols are predefined by gcc in your platform; follow these steps:

$ touch p.c
$ gcc -E -dM p.c

#define __DBL_MIN_EXP__ (-1021)
#define __FLT_MIN__ 1.17549435e-38F
#define __CHAR_BIT__ 8
#define __OpenBSD__ 1
#define __WCHAR_MAX__ 2147483647
#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
#define __FLT_EVAL_METHOD__ 2
#define __unix__ 1
#define __i386__ 1
#define __SIZE_TYPE__ long unsigned int
#define __ELF__ 1
#define __DBL_MIN_10_EXP__ (-307)
#define __FINITE_MATH_ONLY__ 0
#define __GNUC_PATCHLEVEL__ 5
#define __FLT_RADIX__ 2
#define __LDBL_EPSILON__ 1.08420217248550443401e-19L
#define __SHRT_MAX__ 32767
#define __LDBL_MAX__ 1.18973149535723176502e+4932L
#define __LDBL_MAX_EXP__ 16384
#define __LONG_MAX__ 2147483647L
#define __SCHAR_MAX__ 127
#define __DBL_DIG__ 15
#define __USER_LABEL_PREFIX__ 
#define __STDC_HOSTED__ 1
#define __LDBL_MANT_DIG__ 64
#define __FLT_EPSILON__ 1.19209290e-7F
#define __LDBL_MIN__ 3.36210314311209350626e-4932L
#define __WCHAR_TYPE__ int
#define __FLT_DIG__ 6
#define __FLT_MAX_10_EXP__ 38
#define __INT_MAX__ 2147483647
#define __FLT_MAX_EXP__ 128
#define __DECIMAL_DIG__ 21
#define __DBL_MANT_DIG__ 53
#define __WINT_TYPE__ unsigned int
#define __GNUC__ 3
#define __LDBL_MIN_EXP__ (-16381)
#define __LDBL_MAX_10_EXP__ 4932
#define __DBL_EPSILON__ 2.2204460492503131e-16
#define __DBL_MAX__ 1.7976931348623157e+308
#define __DBL_MAX_EXP__ 1024
#define __ANSI_COMPAT 1
#define __FLT_DENORM_MIN__ 1.40129846e-45F
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __FLT_MAX__ 3.40282347e+38F
#define __GXX_ABI_VERSION 102
#define __FLT_MIN_10_EXP__ (-37)
#define __FLT_MIN_EXP__ (-125)
#define i386 1
#define __GNUC_MINOR__ 3
#define __DBL_MAX_10_EXP__ 308
#define __LDBL_DENORM_MIN__ 3.64519953188247460253e-4951L
#define __DBL_MIN__ 2.2250738585072014e-308
#define __PTRDIFF_TYPE__ long int
#define __tune_i386__ 1
#define __LDBL_MIN_10_EXP__ (-4931)
#define __REGISTER_PREFIX__ 
#define __LDBL_DIG__ 18
#define __NO_INLINE__ 1
#define __i386 1
#define __FLT_MANT_DIG__ 24
#define __VERSION__ "3.3.5 (propolice)"

$ rm p.c
$

The output in this example is from a PIII machine running OpenBSD-4.2.

Although the ns-allinone source distribution of the ns-2 network simulator is supposed to compile out of the box for most current architectures, this is not always the case. At least not for ns-2.31^* and Ubuntu 6.06.

[ ./configure && make && make install (or ./install in this case) makes one lazy. Most of the time there is no real difference between this and double clicking SETUP.EXE on a Windows box. That is why I like these problems: They take you back to the good old days, long before autoconf took over the world; when you had to edit files by hand and make changes that varied from changing a line to writing a whole wrapper function in order to compile the damn thing for your system. ]

First:

sudo apt-get install gcc g++ make libc6-dev libx11-dev libxmu-dev

Then change the ./install script inside the ns-allinone-2.31/ directory:

$ diff install install-
483c483
<         ./configure --x-includes=/usr/include || die "otcl-$OTCLVER configuration failed! Exiting ...";
---
>         ./configure || die "otcl-$OTCLVER configuration failed! Exiting ...";
508c508
<         ./configure --x-includes=/usr/include --with-otcl=../otcl-$OTCLVER
|| die "tclcl-$TCLCLVER configuration failed! Exiting ..."
---
>         ./configure --with-otcl=../otcl-$OTCLVER || die "tclcl-$TCLCLVER configuration failed! Exiting ..."
537c537
<         ./configure --x-includes=/usr/include --with-otcl=../otcl-$OTCLVER
--with-tclcl=../tclcl-$TCLCLVER || die "Ns configuration failed! Exiting ...";
---
>         ./configure --with-otcl=../otcl-$OTCLVER --with-tclcl=../tclcl-$TCLCLVER || die "Ns configuration failed! Exiting ...";
570c570
<         ./configure --x-includes=/usr/include --with-otcl=../otcl-$OTCLVER
--with-tclcl=../tclcl-$TCLCLVER || die "Nam configuration failed! Exiting ...";
---
>         ./configure --with-otcl=../otcl-$OTCLVER --with-tclcl=../tclcl-$TCLCLVER || die "Nam configuration failed! Exiting ...";

In a few words, the above diff shows that the ./configure scripts cannot locate the X11 #include files in an Ubuntu system (although they reside under /usr/include) hence the need for –x-includes=/usr/include .

Read also: How to install ns-2.34 on Ubuntu 9.10 Karmic Koala (Ubuntu 9.10).

[*] – ns-2.33 does not require the above hack.