Having issues with mmap from within a function - c++

Question

I'm trying to write a function that has mmap within it, however when I try to access the memory from main(), it gets a segfault. Does anyone have any idea why?
Please ignore the MPI headers - it's for the later part of the project. I have commented out the mprotect line to see that it is an mmap fault as opposed to the handler not necessarily working
net_map.cpp:
#include <iostream>
#include <signal.h>
#include <sys/mman.h>
#include <mpi.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "net_map.h"
using namespace std;
void handler(int sig, siginfo_t* info, void* other)
{
void* address = info->si_addr;
cout << "\nSegfault Detected! [Address: " << address << "]\n" << endl;
int unprotectresult = mprotect(address, SIZE, PROT_READ|PROT_WRITE|PROT_EXEC);
if (unprotectresult == 0)
{
cout << "\nSuccessful mprotect (memory unprotected)!\n" << endl;
}else
{
cout << "\nMprotect unsuccessful\n" << endl;
}
}
void netmap (char filename[], char* mapped)
{
int file;
file = open(filename, O_RDWR);
mapped = (char*) mmap(NULL, SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, file, 0);
if (mapped == MAP_FAILED)
{
cout << "\nMap Failed!" << endl;
}
cout << mapped << endl;
}
main.cpp
#include <iostream>
#include <signal.h>
#include <sys/mman.h>
#include <mpi.h>
#include <unistd.h>
#include <array>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <array>
#include "net_map.h"
using namespace std;
int main(int argc, char* argv[])
{
struct sigaction segaction;
memset(&segaction, 0, sizeof(segaction));
segaction.sa_flags = SA_SIGINFO;
sigemptyset(&segaction.sa_mask);
segaction.sa_sigaction = handler;
sigaction(SIGSEGV, &segaction, NULL);
int i;
char* mapped;
networkpage sheet;
char filename[] = "hello.txt";
netmap(filename, mapped);
sheet.address = (void*)mapped;
cout << "\nAddress: " << sheet.address << endl;
//mprotect(sheet.address, SIZE, PROT_NONE);
memcpy(sheet.address, "k", 1);
munmap(sheet.address, SIZE);
return 0;
}