I like doing this kind of thing all in one regex. This is incomplete, but should be enough to give you the basic idea.

#!/usr/bin/perl

# https://perlmonks.org/?node_id=11105353
# following spirit of my http://www.rosettacode.org/wiki/Compiler/lexi
+cal_analyzer#Alternate_Perl_Solution

use strict;
use warnings;

my @tokens;
my %reserved = map { $_ => 1 } qw(
  alignas alignof and and_eq asm atomic_cancel atomic_commit
  atomic_noexcept auto bitand bitor bool break case catch char
  char16_t char32_t class compl concept const constexpr const_cast
  continue co_await co_return co_yield decltype default delete do
  double dynamic_cast else enum explicit export extern false float for
  friend goto if import inline int long module mutable namespace new
  noexcept not not_eq nullptr operator or or_eq private protected
  public register reinterpret_cast requires return short signed
  sizeof static static_assert static_cast struct switch synchronized
  template this thread_local throw true try typedef typeid typename
  union unsigned using virtual void volatile wchar_t while xor xor_eq
  );
my %Character = ( # Single characters by name
        '(' => 'LeftParen',
        ')' => 'RightParen',
        '[' => 'LeftSquare',
        ']' => 'RightSquare',
        '{' => 'LeftCurly',
        '}' => 'RightCurly',
        '<' => 'LessThan',
        '>' => 'GreaterThan',
        '=' => 'Equal',
        '+' => 'Plus',
        '-' => 'Minus',
        '*' => 'Asterisk',
        '/' => 'Slash',
        '#' => 'Hash',
        '.' => 'Dot',
        ',' => 'Comma',
        ':' => 'Colon',
        ';' => 'Semicolon',
        "'" => 'SingleQuote',
        '"' => 'DoubleQuote',
        '|' => 'Pipe',
    );
my %MultiOps = (
  '>>' => 'RightShift',
  '<<' => 'LeftShift',
  '<=' => 'LessThanOrEqual',
  );
my $regex = qr/ \G (?|
  \s+                 (?{ undef })
  | \/\/.*            (?{ undef })
  | \d+(?:\.\d*)?     (?{ 'Number' })
  | \.\d+             (?{ 'Number' })
  | \w+               (?{ $reserved{$&} ? 'reserved' : 'Identifier' })
  | "([^"]*)"         (?{ [ 'string', $1 ] })
  | (?<!:)::(?!:)     (?{ 'dblColon' })
  | (?:<<|>>|<=)      (?{ $MultiOps{$&} })
  | .                 (?{ $Character{$&} or 'character' })
  ) /x;

$_ = join '', <DATA>;
defined $^R and push @tokens, ref $^R ? $^R : [ $^R, $& ] while /$rege
+x/gc;
use Data::Dump 'dd'; dd @tokens;

__DATA__
// comment should not appear
main(void)
  {
  int foo = 1 << 5;
  puts("testing");
  exit(0); // done
  }
[download]

Outputs:

(
  ["Identifier", "main"],
  ["LeftParen", "("],
  ["reserved", "void"],
  ["RightParen", ")"],
  ["LeftCurly", "{"],
  ["reserved", "int"],
  ["Identifier", "foo"],
  ["Equal", "="],
  ["Number", 1],
  ["LeftShift", "<<"],
  ["Number", 5],
  ["Semicolon", ";"],
  ["Identifier", "puts"],
  ["LeftParen", "("],
  ["string", "testing"],
  ["RightParen", ")"],
  ["Semicolon", ";"],
  ["Identifier", "exit"],
  ["LeftParen", "("],
  ["Number", 0],
  ["RightParen", ")"],
  ["Semicolon", ";"],
  ["RightCurly", "}"],
)
[download]

At least it doesn't fail any of your provided test cases :)

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.