Boost - mmaping a file into memory for reads&writes - c++

Question

I'm trying to map a region of a particular size into the memory, looking at the docs example:
https://www.boost.org/doc/libs/1_70_0/doc/html/interprocess/sharedmemorybetweenprocesses.html#interprocess.sharedmemorybetweenprocesses.mapped_file
as you can notice, boost version is 1.70.0
using namespace boost::interprocess;
const char *FileName = "c_e_d.bin";
const std::size_t FileSize = 10000;
file_mapping::remove(FileName);
std::filebuf fbuf;
auto p = fbuf.open(FileName, std::ios_base::in | std::ios_base::out
| std::ios_base::trunc | std::ios_base::binary);
//Set the size
auto r = fbuf.pubseekoff(FileSize-1, std::ios_base::beg);
auto r2 = fbuf.sputc(0);
//Create a file mapping
file_mapping m_file(FileName, read_write);
//Map the whole file with read-write permissions in this process
mapped_region region(m_file, read_write);
but an exception occurs:
I don't need the parent-child functionality, just many threads writing directly to a mmaped region of memory.
Can somebody help me solve this out please?
Thank you in advance.
Additional debug info:
p is created seemed to be:
It is also seemed to be that the two following operations did work:

Answer 1

Your fbuf doesn't sync. Either sync or limit the scope to get implicit sync on destruction.
#include <boost/interprocess/mapped_region.hpp>
#include <boost/interprocess/file_mapping.hpp>
#include <boost/interprocess/shared_memory_object.hpp>
#include <fstream>
namespace bip = boost::interprocess;
int main()
{
const char* FileName = "c_e_d.bin";
const std::size_t FileSize = 10000;
bip::file_mapping::remove(FileName);
{
std::filebuf fbuf;
/*auto p =*/fbuf.open(FileName,
std::ios_base::in | std::ios_base::out |
std::ios_base::trunc |
std::ios_base::binary);
// Set the size
fbuf.pubseekoff(FileSize - 1, std::ios_base::beg);
fbuf.sputc(0);
fbuf.pubsync();
}
// Create a file mapping
bip::file_mapping m_file(FileName, bip::read_write);
// Map the whole file with read-write permissions in this process
bip::mapped_region region(m_file, bip::read_write);
}