Multiple Definitions Error of Global Arrays [duplicate] - c++

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c++ multiple definitions of a variable
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I am attempting to compile my c++ code, and I continue getting the error:
/tmp/ccEsZppG.o:(.bss+0x0): multiple definition of `mailboxes'
/tmp/ccEZq43v.o:(.bss+0x0): first defined here
/tmp/ccEsZppG.o:(.bss+0xc0): multiple definition of `threads'
/tmp/ccEZq43v.o:(.bss+0xc0): first defined here
/tmp/ccEsZppG.o:(.bss+0x120): multiple definition of `semaphores'
/tmp/ccEZq43v.o:(.bss+0x120): first defined here
collect2: error: ld returned 1 exit status
Here is my code:
addem.cpp
#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <semaphore.h>
#include <pthread.h>
#include "mailbox.h"
using namespace std;
void *sumUp(void *arg);
int main(int argc, char *argv[]) {
int numThreads, minThreads, maxInt, minInt;
if (argc < 3) {
cout << "Error: Need three arguments" << endl;
return 1;
}
numThreads = atoi(argv[1]);
maxInt = atoi(argv[2]);
minThreads = 1;
minInt = 1;
if (numThreads < 1) {
cout << "Cannot work with less than one thread\n"
<< "It's okay but do better next time!\n"
<< "We'll work with 1 thread this time.\n";
numThreads = minThreads;
} else if (numThreads > MAXTHREAD) {
cout << "Sorry, the max for threads is 10.\n"
<< "We'll work with 10 threads this time.\n";
numThreads = MAXTHREAD;
}
if (maxInt < 1) {
cout << "What do you want me to do? I can't count backwards!\n"
<< "I can barely count forwards! Let's make the max number\n"
<< "be 1 to save time\n";
maxInt = minInt;
}
struct msg outgoingMail[numThreads];
int divider = maxInt / numThreads;
int count = 1;
//initialize arrays (mailboxes, semaphores)
for (int i = 0; i < numThreads; i++) {
sem_init(&semaphores[i], 0, 1);
outgoingMail[i].iSender = 0;
outgoingMail[i].type = RANGE;
outgoingMail[i].value1 = count;
count = count + divider;
if (i = numThreads - 1) {
outgoingMail[i].value2 = maxInt;
} else {
outgoingMail[i].value2 = count;
}
}
for (int message = 0; message < numThreads; message++) {
SendMsg(message+1, outgoingMail[message]);
}
int thread;
for (thread = 0; thread <= numThreads; thread++) {
pthread_create(&threads[thread], NULL, &sumUp, (void *)(intptr_t)(thread+1));
}
struct msg incomingMsg;
int total = 0;
for (thread = 0; thread < numThreads; thread++) {
RecvMsg(0, incomingMsg);
total = total + incomingMsg.value1;
}
cout << "The total for 1 to " << maxInt << " using "
<< numThreads << " threads is " << total << endl;
return 0;
}
void *sumUp(void *arg) {
int index,total;
index = (intptr_t)arg;
struct msg message;
RecvMsg(index, message);
message.iSender = index;
message.type = ALLDONE;
total = 0;
for (int i = message.value1; i <= message.value2; i++) {
total += i;
}
SendMsg(0, message);
return (void *) 0;
}
mailbox.cpp
#include <stdio.h>
#include <iostream>
#include "mailbox.h"
using namespace std;
int SendMsg(int iTo, struct msg &Msg) {
if (safeToCall(iTo)) {
cout << "Error calling SendMsg" << endl;
return 1;
}
sem_wait(&semaphores[iTo]);
mailboxes[iTo] = Msg;
sem_post(&semaphores[iTo]);
return 0;
}
int RecvMsg(int iFrom, struct msg &Msg) {
sem_wait(&semaphores[iFrom]);
if (safeToCall(iFrom)) {
cout << "Error calling RecvMsg" << endl;
return 1;
}
mailboxes[iFrom] = Msg;
sem_post(&semaphores[iFrom]);
return 0;
}
bool safeToCall(int location) {
bool safe = !(location < 0 || location > MAXTHREAD + 1);
return safe;
//return true;
}
mailbox.h
#ifndef MAILBOX_H_
#define MAILBOX_H_
#define RANGE 1
#define ALLDONE 2
#define MAXTHREAD 10
#include <semaphore.h>
#include <pthread.h>
struct msg {
int iSender; /* sender of the message (0 .. numThreads)*/
int type; /* its type */
int value1; /* first value */
int value2; /* second value */
};
struct msg mailboxes[MAXTHREAD + 1];
pthread_t threads[MAXTHREAD + 1];
sem_t semaphores[MAXTHREAD + 1];
int SendMsg(int iTo, struct msg &Msg);
int RecvMsg(int iFrom, struct msg &Msg);
bool safeToCall(int location);
#endif
I am compiling the code with the command
g++ -o addem addem.cpp mailbox.cpp -lpthread
I have tried commenting out all of the function bodies in the source code to leave them as stub functions, and the same error occurs. The only way I have been able to compile the file is if I comment out the function bodies, and remove
#include "mailbox.h"
From at least one of the files. I feel it has to do with how I am initializing the arrays? But I cannot figure out a workaround.