pointer get wrong value in different thread

I am writing a piece of code to demonstrate the multi-threading share memory writing.

However, my code gets a strange 0xffffffff pointer I can't make out why. I haven't been writing cpp code for a while. please let me know if I get something wrong.

I compile with the command: g++ --std=c++11 shared_mem_multi_write.cpp -lpthread -g

I get error echoes like:

function base_ptr: 0x5eebff, src_ptr: 0x7f21a9c4e010, size: 6220800
function base_ptr: 0xffffffffffffffff, src_ptr: 0x7f21a9c4e010, size: 6220800
function base_ptr: 0xbdd7ff, src_ptr: 0x7f21a9c4e010, size: 6220800
function base_ptr: 0x23987ff, src_ptr: 0x7f21a9c4e010, size: 6220800
function base_ptr: 0x11cc3ff, src_ptr: 0x7f21a9c4e010, size: 6220800
function base_ptr: 0x17bafff, src_ptr: 0x7f21a9c4e010, size: 6220800
function base_ptr: 0x1da9bff, src_ptr: 0x7f21a9c4e010, size: 6220800
Segmentation fault (core dumped)

my os is CentOS Linux release 7.6.1810 (Core) gcc version 4.8.5 and the code is posted below:

#include <chrono>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iostream>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <thread>
#include <vector>
#include <memory>

const size_t THREAD_CNT = 40;
const size_t FRAME_SIZE = 1920 * 1080 * 3;
const size_t SEG_SIZE = FRAME_SIZE * THREAD_CNT;

void func(char *base_ptr, char *src_ptr, size_t size)
{
    printf("function base_ptr: %p, src_ptr: %p, size: %u\n", base_ptr, src_ptr, size);
    while (1)
    {
        auto now = std::chrono::system_clock::now();
        memcpy(base_ptr, src_ptr, size);
        std::chrono::system_clock::time_point next_ts =
            now + std::chrono::milliseconds(42); // 24 frame per seconds => 42 ms per frame
        std::this_thread::sleep_until(next_ts);
    }
}

int main(int argc, char **argv)
{
    int shmkey = 666;
    int shmid;
    shmid = shmget(shmkey, SEG_SIZE, IPC_CREAT);
    char *src_ptr = new char[FRAME_SIZE];
    char *shmpointer = static_cast<char *>(shmat(shmid, nullptr, 0));
    std::vector<std::shared_ptr<std::thread>> t_vec;
    t_vec.reserve(THREAD_CNT);
    for (int i = 0; i < THREAD_CNT; ++i)
    {
        //t_vec[i] = std::thread(func, i * FRAME_SIZE + shmpointer, src_ptr, FRAME_SIZE);
        t_vec[i] = std::make_shared<std::thread>(func, i * FRAME_SIZE + shmpointer, src_ptr, FRAME_SIZE);
    }
    for (auto &&t : t_vec)
    {
        t->join();
    }
    return 0;
}