Warning: This challenge is only valid for languages with a compiler.

Make a program (which is perfectly valid code) that outputs Hello, World, even before runtime.

How? Let me explain.

Many languages have a compiler. Some operations are made in the compile-time, and others, in runtime. You trick the compiler to output the text Hello, World in compile-time. The text can be anywhere, like the build log.(Not errors. sorry for invalidating all those answers. at least theres pragma tho)

You can use C, C++ or C#, but I wouldn't encourage you to. It's simply a game breaker.

p.s. I wrote this challenge because the tag is both unused, and used wrong.

  • 8
    Wouldn't the simple source code Hello, World! be optimal in almost any compiled language where that line is not valid code and the offending line gets printed in an error message? – Martin Ender Jul 5 '17 at 9:15
  • 3
    "which is perfectly valid code" ... "The text can be anywhere, like the build log, an error, anywhere" ... what's "perfectly valid code" then? – Martin Ender Jul 5 '17 at 9:22
  • 1
    I would say, better ask the “Hello, World!” to appear both when compiling and when running. That would make clear what is valid code. – manatwork Jul 5 '17 at 9:25
  • @manatwork Or use two different strings so that you can't just get the line output during compiling that has the string for the actual running. – Martin Ender Jul 5 '17 at 9:26
  • 1
    Are custom file names allowed? – Okx Jul 5 '17 at 10:53

C#, 51 bytes

Try it online

#warning Hello, World
class P{static void Main(){}}

Prints the following to the Error List (but still compiles):

warning CS1030: #warning: `Hello, World'
  • OP has updated that errors are not allowed. Just use #warning instead. – TheLethalCoder Jul 5 '17 at 9:33

C (gcc), 22 18 bytes

Hello, World;main;

This compiles just fine with gcc (and clang), although the program it produces crashes immediately.

Try it online!

Compiler output

gcc 6.3.1 produces the following debugging information.

.code.tio.c:1:1: warning: data definition has no type or storage class
 Hello, World;main;
.code.tio.c:1:1: warning: type defaults to ‘int’ in declaration of ‘Hello’ [-Wimplicit-int]
.code.tio.c:1:8: warning: type defaults to ‘int’ in declaration of ‘World’ [-Wimplicit-int]
 Hello, World;main;
.code.tio.c:1:14: warning: data definition has no type or storage class
 Hello, World;main;
.code.tio.c:1:14: warning: type defaults to ‘int’ in declaration of ‘main’ [-Wimplicit-int]

C (gcc), 15 bytes

Hello, World;

If compiling to an object file is allowed, this works just as well. The resulting file simply declares two global variables.

The byte count includes +3 bytes for the compiler flag -c.

Try it online!

Compiler output

hw.c:1:1: warning: data definition has no type or storage class
 Hello, World;
hw.c:1:1: warning: type defaults to ‘int’ in declaration of ‘Hello’ [-Wimplicit-int]
hw.c:1:8: warning: type defaults to ‘int’ in declaration of ‘World’ [-Wimplicit-int]
 Hello, World;

C (gcc), 20 bytes

main(Hello, World){}

This compiles to a program that exits cleanly.

Try it online!

Compiler output

.code.tio.c:1:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
 main(Hello, World){}
.code.tio.c: In function ‘main’:
.code.tio.c:1:1: warning: type of ‘Hello’ defaults to ‘int’ [-Wimplicit-int]
.code.tio.c:1:1: warning: type of ‘World’ defaults to ‘int’ [-Wimplicit-int]
  • 1
    Weird, I swear I tried this and it didn't work for me. Have an upvote – musicman523 Jul 5 '17 at 18:53

FreePascal, 29 characters

begin{$INFO Hello, World}end.

Maybe other Pascal variants too, not sure whether the $INFO directive is FreePascal only or not.

Sample run:

bash-4.4$ fpc compile-time-message.pas 
Free Pascal Compiler version 3.0.2+dfsg-2 [2017/04/09] for x86_64
Copyright (c) 1993-2017 by Florian Klaempfl and others
Target OS: Linux for x86-64
Compiling compile-time-message.pas
User defined: Hello, World
Linking compile-time-message
/usr/bin/ld.bfd: warning: link.res contains output sections; did you forget -T?
0 lines compiled, 0.0 sec

Haskell, 25 24 bytes


8 bytes from the code plus 16 bytes for the compiler flag -W'Hello, World'.

Gives the warning unrecognised warning flag: -WHello, World and compiles the program.

Depending on the shell (or the absence of a shell) you can omit the single quotes in the flag for two bytes less. TIO works this way.

Haskell, TIO environment, 22 bytes

Try it online!

Edit: @Dennis saved a byte. Thanks!

Perl, 15 bytes

14 bytes of code + -w flag.

"Hello, World"

When ran with -w flag, it produces the compile-time warnings:

$ perl -we '"Hello, World"'
Useless use of a constant ("Hello, World") in void context at -e line 1.

And if you wonder if it really happens at compile time, you can add -c flag, which causes the program to be compiled but not ran, and the warning is still here.

C (gcc), 23 bytes

main(){"Hello, World";}

Try it online!

Gives the warning:

warning: return type defaults to ‘int’ [-Wimplicit-int]
main(){"Hello, World";}

C (gcc), 38 bytes

#pragma message"Hello, World"

Try it online!

Rather than using compiler warnings, this answer uses a built-in pragma directive that allows printing notes to stdout. Works in C and C++ (as I think all the rest of these do).

C (gcc), 23 + 1 = 24 bytes

#define f"Hello, World"

Try it online!

Prints "Hello, World!" as part of an error message, which says:

warning: ISO C99 requires whitespace after the macro name
 #define f"Hello, World!"

This is a default warning in GCC; no flags need to be added to achieve this.

The extra byte comes from the -c flag, which successfully compiles the program without linking, which means it accepts not having a main function. However, the resulting output file cannot be executed. If this is unacceptable, then:

C (gcc), 31 bytes

#define f"Hello, World"

Try it online!

This will run, but will segfault every time. If that's not acceptable, then:

C (gcc), 32 bytes

#define f"Hello, World"

Try it online!

  • -c counts as three bytes (one for the space). main=0; is the same as main;. #define Hello, World is shorter than #define f"Hello, World". – Dennis Jul 5 '17 at 22:53

Scala, 36 bytes

object F extends App{"Hello, World"}

Try it online!

Gives the warning:

warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
object F{"Hello, World"}

GNU C, 31 bytes

Nothing clever here. I'm mostly posting it for reference.

main(){printf("Hello, World");}

GCC will throw the following warning at compilation time:

hello.c: In function ‘main’:
hello.c:1:8: warning: incompatible implicit declaration of built-in function ‘printf’ [enabled by default]
 main(){printf("Hello, World");}
  • Can't you use puts for -2? – Erik the Outgolfer Jul 5 '17 at 14:54
  • @EriktheOutgolfer With my version of GCC at least, puts() would compile without a warning. – Arnauld Jul 5 '17 at 14:56
  • Can you use f instead of main? – musicman523 Jul 5 '17 at 15:26
  • @musicman523 Would a C program without a main() compile at all? – Arnauld Jul 5 '17 at 17:29
  • @Arnauld You could use the -c flag to compile without linking, it would just be unexecutable. – musicman523 Jul 5 '17 at 18:29

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