How many asterisks can be put?

#c #clang #gcc

In C and C++, the asterisk (*) is used to declare or dereference a pointer variable.

By the way, did you know that you can prefix a function call with as many asterisks as you like?

Here is the simple and valid C program.

#include <stdio.h>

int main(){
  printf("Hello world!\n");
}

Here is a valid C program too.

#include <stdio.h>

int main(){
  (*printf)("Hello world!\n");
}

Here is also a valid one.

#include <stdio.h>

int main(){
  (******printf)("Hello world!\n");
}

This program with 100 asterisks is also a perfect C program.

#include <stdio.h>

int main(){
  (
   **********
   **********
   **********
   **********
   **********
   **********
   **********
   **********
   **********
   **********
   printf)("Hello world!\n");
}

You see this and you're wondering how many asterisks you can add? Let's find out.

This is a Ruby script that prepends the specified number of asterisks to the printf function.

def check(n)
  s = "*"*n
  open("test.c","w") do |f|
  f.puts <<EOS
#include <stdio.h>
int main(){
(#{s}printf)("Hello World!\\n");
}
EOS
end
  return system("clang test.c")
end

check(ARGV[0].to_i)

You can use like this.

ruby check.rb 10

It will generate a following source codes.

#include <stdio.h>
int main(){
(**********printf)("Hello World!\n");
}

Let's try it with a thousand asterisks.

ruby check.rb 1000

No problem. Then try with ten thousand.

ruby check.rb 10000
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
(snip)
clang-12: error: unable to execute command: Segmentation fault (core dumped)
clang-12: error: clang frontend command failed due to signal (use -v to see invocation)

Clang died with SIGSEGV.

Clang was ok with 1000 asterisks and died with 10,000 asterisks. So there must be a limit somewhere in there. Let's check it out with a binary search.

def check(n)
  s = "*"*n
  open("test.c","w") do |f|
  f.puts <<EOS
#include <stdio.h>
int main(){
(#{s}printf)("Hello World!\\n");
}
EOS
end
  if system("clang test.c 2> /dev/null")
    puts "#{n} OK"
    false
  else
    puts "#{n} NG"
    true
  end
end

(1000..10000).bsearch do |n|
  check(n)
end

Here is the execution result.

$ ruby search.rb
5500 NG
3250 NG
2125 NG
1562 OK
1844 NG
1703 NG
1633 OK
1668 NG
1651 OK
1660 NG
1656 OK
1658 NG
1657 OK

Now, we have new knowledge. We can put up to 1657 asterisks (environment dependent).

By the way, let's try it with GCC. Here is a check script.

def check(n)
  s = "*"*n
  open("test.c","w") do |f|
  f.puts <<EOS
#include <stdio.h>
int main(){
(#{s}printf)("Hello World!\\n");
}
EOS
end
  return system("gcc test.c")
end

check(ARGV[0].to_i)

Let's try from 1000.

ruby check_gcc.rb 1000

No problem. Next, 10,000.

ruby check_gcc.rb 10000

Well, how about 100,000?

ruby check_gcc.rb 100000

Seriously? Then, 1,000,000.

$ ruby check_gcc.rb 1000000
gcc: internal compiler error: Segmentation fault signal terminated program cc1
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://bugzilla.redhat.com/bugzilla> for instructions.

Oops, gcc dided with a million of asterisks.

So, If you want to use ten thousand asterisks, use GCC.