The obligatory PHP one (which still hasn't been fixed as of 5.4):

<?:: 

Outputs:

Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM on line 1

Whaa?

Gcc compile error:

int main() { long long long a; } 

error: long long long is too long for GCC

Windows Command Prompt

If you're happy and you know it clap your hands! 

Output:

happy was unexpected at this time.

PHP

$ cat error.php <?php function echo_string(string $string) { echo $string; } echo_string("Hello, world!"); $ php error.php PHP Catchable fatal error: Argument 1 passed to echo_string() must be an instance of string, string given, called in error.php on line 5 and defined in error.php on line 2 

You cannot pass a string to a function, you have to pass a string instead!

Update: This code is NOT an error in PHP 7. Hover on/click/touch a spoiler to check why (contains spoilers about how the code works).

A new feature known as scalar type declarations was added in PHP 7. This feature allows using scalar types in function declarations.

bash

$ echo "Hello, world!" bash: !": event not found 

And you would think that bash would accept a simple "Hello, world!" program.

Python 2.7

# Look I'm actually coding: see my happy face? print ':)' 

Generates the rather unhelpful:

SyntaxError: encoding problem: with BOM 

How can a simple comment generate an error?

Mathematica

When using Mathematica to create graphical output, one sometimes triggers error messages formatted according to specifications being used in the program itself. Here is a trivial example.

Rotate[f/0, .6] 

TI-89 Graphing Calculator

I discovered this when learning about implicit differentiation in high school calculus. If you input:

d(xy+x=0,x) 

You get the following:

1 = 0 

With this caveat, printed in tiny letters at the bottom of the screen:

Warning: May produce false equation 

This happens because xy is not interpreted as x * y, but rather as its own symbol, xy.

Oddly, if you do d(xy=0,x), you get 0 = 0 with the same warning.

You can make the Haskell compiler's brain explode:

C:\Windows\system32>ghci ... Prelude> :set -XExistentialQuantification Prelude> data Foo = forall a. Foo a Prelude> let foo f = 1 where Foo a = f <interactive>:4:21: My brain just exploded I can't handle pattern bindings for existential or GADT data constructors. Instead, use a case-expression, or do-notation, to unpack the constructor. In the pattern: Foo a In a pattern binding: Foo a = f In an equation for `foo': foo f = 1 where Foo a = f Prelude> 

Ruby

Rules abuse.

class StandardError def to_s words = File.open('/usr/share/dict/words'){|f|f.readlines.map &:chop}.sample(100) words.last.capitalize! super.gsub(/\w+/){words.pop} end to_s(3) end 

If run on OSX, produces, e.g.

$ ruby weird_runtime_error.rb weird_runtime_error.rb:9:in `to_s': Sculpturation contingence explicate tappet(phonendoscope ethopoeia nannandrous) (ArgumentError) from weird_runtime_error.rb:9:in `<class:StandardError>' from weird_runtime_error.rb:1:in `<main>' 

DOS Prompt

c:\>make love 

gives you

Fatal Error: 'love' does not exist. Don't know how to make it. 

Stumbled upon this while I was trying to insult my computer for being uncooperative. Made me kinda sad for a while until I found out, that this only happens if love does not exist. If it exists he will gladly make it.

Bash (Quine error)

This error is a Quine in Bash!

$ bash: bash:: command not found... bash: bash:: command not found... 

Of course you must have the relevant locale (english here).

CSH

A really classical csh joke:

% make fire? make: No match. 

Bash - accurate recreation of a rare historical error message

echo -ne $(tail -n +257 /usr/src/linux*/drivers/char/lp.c | head -1 | cut -d '"' -f 2 | sed 's/%d/0/') 

Output:

lp0 on fire 

Requires the linux kernel source to be unpacked in the usual place.

Fun fact: i once received this message in earnest, when running an old ribbon printer.

Ruby

Feel like it's weird that this can happen in a high-level language.

$*<<$*<<$**$/ 

produces

ArgumentError: recursive array join 

C(++)

If compile-time errors count here's one (assuming a file named "crash.c").

#include "crash.c" int main(){ return 0; } 

It fills the screen with this upon compilation (have Ctrl-C ready)

 from crash.c:1, from crash.c:1: crash.c:3:1: error: redefinition of ‘main’ crash.c:3:1: note: previous definition of ‘main’ was here In file included from crash.c:1:0, from crash.c:1, from crash.c:1, 

Another snippet which compiles perfectly well (no warnings under -Wall and illustrates the beautiful type safety of C </s>

#include <stdio.h> int i; int main(){ sprintf(NULL, "%s", (char *) (void *) (1/i)); return 0; } 

Running it gives:

Floating point exception (core dumped) 

This is very old, but for those who remember BCPL,

GET "LIBHDR" LET START() = VALOF $8 RESULTIS 0 $) 

would complain

$8 ^ "( ) or 8 expected" 

R

This is technically not an error but a warning but nevertheless it's ridiculous, and occurs for completely esoteric reasons.

[[EDIT]] It seems that the cause of some parts of the funny warnings resides in RStudio rather than R per se, so it's less interesting than I first thought. The first example i.e plot(1:2, NotAGraphicalParameter = "ignore.me") is, however, still reproducible in "naked" R and is funny enough on its own right.[[/EDIT]]

> plot(1:2, NotAGraphicalParameter = "ignore.me") # produces a nice scatterplot with two points, [1,1] and [2,2] Warning messages: 1: In plot.window(...) : "NotAGraphicalParameter" is not a graphical parameter 2: In plot.xy(xy, type, ...) : "NotAGraphicalParameter" is not a graphical parameter 3: In axis(side = side, at = at, labels = labels, ...) : "NotAGraphicalParameter" is not a graphical parameter 4: In axis(side = side, at = at, labels = labels, ...) : "NotAGraphicalParameter" is not a graphical parameter 5: In box(...) : "NotAGraphicalParameter" is not a graphical parameter 6: In title(...) : "NotAGraphicalParameter" is not a graphical parameter > plot(2:3) # another nice scatterplot: [2,2] and [3,3] # but there should be nothing wrong this time! # however ... There were 12 warnings (use warnings() to see them) > warnings() Warning messages: 1: "NotAGraphicalParameter" is not a graphical parameter 2: "NotAGraphicalParameter" is not a graphical parameter 3: "NotAGraphicalParameter" is not a graphical parameter 4: "NotAGraphicalParameter" is not a graphical parameter 5: "NotAGraphicalParameter" is not a graphical parameter 6: "NotAGraphicalParameter" is not a graphical parameter 7: "NotAGraphicalParameter" is not a graphical parameter 8: "NotAGraphicalParameter" is not a graphical parameter 9: "NotAGraphicalParameter" is not a graphical parameter 10: "NotAGraphicalParameter" is not a graphical parameter 11: "NotAGraphicalParameter" is not a graphical parameter 12: "NotAGraphicalParameter" is not a graphical parameter # but let's try once more: > plot(2:3) # yup. no warnings this time. we had to do it twice 

It's like R remembers our insults. But not for long.

I can't really explain why this happens - but it is reproducible. Actually it occurs every time when you supply some "not a graphical parameter" to plot 1, and then do a plot 2 in a completely impeccable way. It is especially funny that we get 12 "not a graphical parameter" warnings for the second plot but only 6 for the first one. Another funny thing is that if you supply "not a graphical parameter" with a value NULL then no condition is thrown:

plot(1:2, Nonsense=NULL) # no warnings # however plot(1:2, Nonsense="gibberish") # gives the usual 6-pack of warnings 

And to get even more ridiculous, let's draw some lines on top of the previously drawn plot:

plot(1:2) # you will see the number of warnings growing with each line: lines(1:2, 1:2, mumbo = 1) lines(1:2, 1:2, jumbo = 2) lines(1:2, 1:2, bimbo = 3) lines(1:2, 1:2, cucaracha = 4) lines(1:2, 1:2, karaoke = 5) lines(1:2, 1:2, radiogaga = 6) lines(1:2, 1:2, reptiles = 7) lines(1:2, 1:2, cowsonmoon = 8) lines(1:2, 1:2, stainlessSteelLadderToTheMoon = 9) lines(1:2, 1:2, frambuesa = 10) lines(1:2, 1:2, fresa = 11) lines(1:2, 1:2, limonYNada = 12) lines(1:2, 1:2, slingsAndArrows = 13) # ... and now you have 25 warnings: warnings() Warning messages: 1: "mumbo" is not a graphical parameter 2: "jumbo" is not a graphical parameter 3: "bimbo" is not a graphical parameter 4: "cucaracha" is not a graphical parameter 5: "karaoke" is not a graphical parameter 6: "radiogaga" is not a graphical parameter 7: "reptiles" is not a graphical parameter 8: "cowsonmoon" is not a graphical parameter 9: "stainlessSteelLadderToTheMoon" is not a graphical parameter 10: "frambuesa" is not a graphical parameter 11: "fresa" is not a graphical parameter 12: "limonYNada" is not a graphical parameter 13: "mumbo" is not a graphical parameter 14: "jumbo" is not a graphical parameter 15: "bimbo" is not a graphical parameter 16: "cucaracha" is not a graphical parameter 17: "karaoke" is not a graphical parameter 18: "radiogaga" is not a graphical parameter 19: "reptiles" is not a graphical parameter 20: "cowsonmoon" is not a graphical parameter 21: "stainlessSteelLadderToTheMoon" is not a graphical parameter 22: "frambuesa" is not a graphical parameter 23: "fresa" is not a graphical parameter 24: "limonYNada" is not a graphical parameter 25: In plot.xy(xy.coords(x, y), type = type, ...) : "slingsAndArrows" is not a graphical parameter 

This should not win big time unless there is no justice.

Windows Command Script

WARNING, this is a fork bomb!

This will output garbage questions about quitting if you try to quit the console in any way.

%0|%0|%0 

Bonuses:

• Will make the system pretty much unusable until restart
• Prevents quitting the script, which should be impossible

How about compiler optimisation errors:

#include <stdio.h> #define N 4 int main(void) { int sum; int i; int arr[N]; for (i = 0, sum = 0; i < N; i++, arr[i] = sum) { sum += arr[i]; } printf("%d\n", sum); return 0; } 

This is specific to gcc >= 4.7. Compiles and runs fine with gcc -O0 -Wall. Compiles with gcc -O2 -Wall but results in an inf-loop.

Also note, how gcc does see the problem for smaller N, e.g. N = 3:

test.c:11:38: warning: array subscript is above array bounds [-Warray-bounds] for (i = 0, sum = 0; i < N; i++, arr[i] = sum) { ^ test.c:12:13: warning: 'arr[0]' is used uninitialized in this function [-Wuninitialized] sum += arr[i]; ^ 

Btw, this has been taken from a bug report, I can't recall the bug number though.

I've always liked this weirdness in APL:

 ⍝ obviously a syntax error { (] } 3 SYNTAX ERROR {(]}3 ⍝ but: { (] } 1÷0 DOMAIN ERROR {(]}1÷0 ⍝ it even works with statically defined functions ∇z←f x [1] z←[{]}x [2] ∇ f 1÷0 DOMAIN ERROR f 1÷0 ∧ f 3 SYNTAX ERROR f[1] z←[{]}x 

It parses the inside of functions lazily!

q insults you

q)`u#1 1 'u-fail q) 

```u#`` tells q that every element in a list is unique (so it can build some sort of hash-based index, presumably). this is what happens when it's not actually true.

Python

Nested blocks

for a in range(26): for b in range(26): for c in range(26): for d in range(26): for e in range(26): for f in range(26): for g in range(26): for h in range(26): for i in range(26): for j in range(26): for k in range(26): for l in range(26): for m in range(26): for n in range(26): for o in range(26): for p in range(26): for q in range(26): for r in range(26): for s in range(26): for t in range(26): for u in range(26): for v in range(26): for w in range(26): for x in range(26): for y in range(26): for z in range(26): print a 

Python 2.7: SystemError: too many statically nested blocks

Self-referencing lists

def printList(myList): for element in myList: if isinstance(element, list): printList(myList) else: print(element) a = [] a.append(a) printList(a) 

Python 2.7

True is not a constant

The problem in the following example is that in Python 2.7, True and False are not constants. And True and False can automatically get casted to 1 and 0:

True=False a=10/True Traceback (most recent call last): File "/home/moose/.config/pluma/tools/new-tool-2", line 11, in <module> exec(sys.stdin.read()) File "<string>", line 2, in <module> ZeroDivisionError: integer division or modulo by zero 

Python 2.7:

Intendation

def f(n): if n <= 1: return n else: return f(n-1)+f(n-2) 

Do you get the error?

Traceback (most recent call last): File "/home/moose/.config/pluma/tools/new-tool-2", line 11, in <module> exec(sys.stdin.read()) File "<string>", line 4 else: ^ SyntaxError: invalid syntax 

Mixing tabs and spaces was ok in Python 2.7 ... but mind the indentation level!

I'll start:

#include <iostream> using namespace std; class A { public: A() { } void doSomethingDiabolical() { delete this; } virtual void breakHorribly() { cout << "still alive" << endl; doSomethingDiabolical(); cout << "still alive" << endl; } }; class B : public A { public: B() : A() { } void breakHorribly() { cout << "still alive" << endl; ((A *) this)->breakHorribly(); cout << "still alive" << endl; doSomethingDiabolical(); cout << "still alive" << endl; breakHorribly(); cout << "dead" << endl; } }; int main() { jane(); } void jane() { cout << "still alive" << endl; A * o = new B; cout << "still alive" << endl; o->breakHorribly(); } 

Any guesses why this program crashes? :D

See jane run: http://ideone.com/gtaZ3

CPython

import ctypes import sys (ctypes.c_char * sys.getsizeof(None)).from_address(id(None))[:4] = '\x00' * 4 

The result:

Fatal Python error: deallocating None This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. 

PHP

<?php [][] = 42; 

[] is used in order to push elements. However, if you use it for array literal, the PHP makes crazy error message, even if you assign to it in order to push. Requires PHP >= 5.4, as before that you couldn't have indexed array literals.

Output:

Fatal error: Cannot use [] for reading in [...][...] on line 2

TeX

This simple TeX program:

\def~{x~}~ 

gives the following error in the log file:

! TeX capacity exceeded, sorry [main memory size=5000000]. l.1 \def~{x~}~ If you really absolutely need more capacity, you can ask a wizard to enlarge me. 

You better know which wizard it the right wizard :-)

TeX: second error message

This is a small LaTeX table with 260 columns, for which we want a cell that spans all the columns.

\documentclass{article} \begin{document} \begin{tabular}{*{260}{l}} \multicolumn{260}{c}{Table Title} \end{tabular} \end{document} 

The error message is also hilarious:

! This can't happen (256 spans). <template> \endtemplate l.5 \end{tabular} I'm broken. Please show this to someone who can fix can fix 

How many programs are humble enough to admit they are broken?

R

Another one which is not ridiculous and, again, a warning rather than an error, but still nice:

> sapply(as.list(-1:-51), log) [1] NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN [20] NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN [39] NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN There were 50 or more warnings (use warnings() to see the first 50) 

I like the last bit: 50 or more :)

And the actual warnings:

1: In lapply(X = X, FUN = FUN, ...) : NaNs produced 2: In lapply(X = X, FUN = FUN, ...) : NaNs produced .... 50: In lapply(X = X, FUN = FUN, ...) : NaNs produced 

FUN = FUN!

C# - Recursive, lazy Fibonacci generator

static void Main() { Console.WriteLine(string.Join(",", fib().Take(141))); Console.ReadLine(); } static IEnumerable<decimal> fib(decimal n = 0, decimal m = 1) { if (n == 0) { yield return 0; yield return 1; } while (true) { yield return n + m; foreach(var x in fib(m, n+m)) { yield return x; } } } 

This code looks fine, right? A fairly simple Fibonacci generator, spiced up with some recursion and lazy enumeration. Should work.

Nope! Running this will cause an OverflowException. This is because we are using decimal, and the 141st Fibonacci number (~8.1E28) exceeds the maximum value of decimal (~7.9E28).

The int, however does not throw an OverflowException when you exceed its maximum value. Instead it, as expected, overflows to a negative value. So if we replace int instead with decimal, like in the following code, it should work, right?

static void Main() { Console.WriteLine(string.Join(",", fib().Take(141))); Console.ReadLine(); } static IEnumerable<int> fib(int n = 0, int m = 1) { if (n == 0) { yield return 0; yield return 1; } while (true) { yield return n + m; foreach(var x in fib(m, n+m).ToList()) { yield return x; } } } 

If you read the code it should be obvious why this won't work. If you didn't... I didn't just change the type from decimal to int; I also snuck in a call to ToList() in the foreach statement. This will force the enumerator returned to be eagerly evaluated. This will cause not 141 recursions, but instead an infinite number of recursions. Actually, long before it hits infinity it will of course overflow the stack, causing the runtime to throw a StackOverflowException. (bonus: this exception cannot be caught, so it will crash the runtime)

Bash

I got this today when I tried to find out whether it is possible to protect the system from rm -rf /.

mkdir /tmp/a mkdir /tmp/a/b sudo mount --bind /tmp/a /tmp/a/b rm -rf /tmp/a 

The error message with LANG=C:

rm: WARNING: Circular directory structure. This almost certainly means that you have a corrupted file system. NOTIFY YOUR SYSTEM MANAGER. The following directory is part of the cycle: '/tmp/a/b'