Makefile duplicate symbol

I want to take a brief moment that I'm aware SO is littered with these questions and I've looked at many:

I'm currently building a disassembler for a school project using C++ and I'm getting blasted with duplicate symbol errors when I run my make file. I fear my issue is a little more complicated than the examples cited above. I apologize for the duplicate question but I can't figure it out after hours of searching and attempting to fix the issue and I appreciate any constructive, complete, and positive feedback anyone has.

g++ version 3.4.6 (yes, I know, it's old – school server)
make version 3.81

Here's my makefile:

CC=g++
CFLAGS=-Wall -O0 -c

all: dasm

dasm: main.o optab.o record_tokenizer.o regex.o
    $(CC) -o $@ $^

clean:
    rm *.o dasm

It looks like Make is able to convert all files to their respective object files but the linking into the single executable is what's failing:

c++    -c -o main.o main.cpp
c++    -c -o optab.o optab.cpp
c++    -c -o record_tokenizer.o record_tokenizer.cpp
c++    -c -o regex.o regex.cpp
g++ -o dasm main.o optab.o record_tokenizer.o regex.o
duplicate symbol _optab in:
    main.o
    optab.o
duplicate symbol _optab in:
    main.o
    record_tokenizer.o
duplicate symbol _HEADER_RECORD_REGEX in:
    main.o
    record_tokenizer.o
duplicate symbol _END_RECORD_REGEX in:
    main.o
    record_tokenizer.o
duplicate symbol _TEXT_RECORD_REGEX in:
    main.o
    record_tokenizer.o
duplicate symbol _MOD_RECORD_REGEX in:
    main.o
    record_tokenizer.o
ld: 6 duplicate symbols for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [dasm] Error 1

I'm definitely not a C++ expert nor am I a Makefile guru so any help is appreciated. Here are the relevant files:

optab.h

#ifndef __dasm__optab__
#define __dasm__optab__

#include <map>
#include <string>

std::map<short, const char*> optab;

void init_optab();
const char* get_instruction(int n);

#endif

regex.h

#ifndef __dasm__regex__
#define __dasm__regex__

#include <regex.h>

bool match(const char* pattern, const char* string);

#endif

record_tokenizer.h

#ifndef __dasm__record_tokenizer__
#define __dasm__record_tokenizer__

#include <vector>
#include <cstdlib>
#include <sstream>
#include "regex.h"
#include "optab.h"

const char* HEADER_RECORD_REGEX = "^H[a-zA-Z|[:space:]]{6}[:digit:]{12}";
const char* END_RECORD_REGEX = "^E([:digit:]{6})?";
const char* TEXT_RECORD_REGEX = "^T[:digit:]{6}[0-1][0-E][:digit:]{,60}"; // TODO: improve on this
const char* MOD_RECORD_REGEX = "^M[:digit:]{8}";

struct Record {
    char record_type;
    std::string name;
    std::string address;
    std::vector<std::string> addresses; // used for T records only
};


bool is_valid_record(const char* record, const char* pattern);
const int to_i(std::string n);
const Record tokenize_record(std::string record);

#endif

main.cpp

#include <iostream>
#include "record_tokenizer.h"

using namespace std;

int main(int args, const char* argv[]) {
    if(args > 2) {
        std::cerr << "Usage: dasm sample.obj" << std::endl;
        exit(EXIT_FAILURE);
    }
    tokenize_record("T0000001E^050000^032003^3F^69101791^1BA0131BC0002F200A3B2FF40F102F014F0000");

    return 0;
}

Solution

This line in optab.h is a problem:

std::map<short, const char*> optab;

Every .cpp file that includes this .h file defines optab as a global variable. That would result in the symbol defined multiple times.

Same errors will result from the lines:

const char* HEADER_RECORD_REGEX = "^H[a-zA-Z|[:space:]]{6}[:digit:]{12}";
const char* END_RECORD_REGEX = "^E([:digit:]{6})?";
const char* TEXT_RECORD_REGEX = "^T[:digit:]{6}[0-1][0-E][:digit:]{,60}";
const char* MOD_RECORD_REGEX = "^M[:digit:]{8}";

in record_tokenizer.h.

You can fix them by:

By making them extern variables and defining them in only one .cpp file.
By making them static variables.

By making them const. This would work for the strings but not optab. I imagine you will need to change its value.

const char* const HEADER_RECORD_REGEX =  ...;
const char* const END_RECORD_REGEX = ...;
const char* const TEXT_RECORD_REGEX = ...;
const char* const MOD_RECORD_REGEX = ...;