Play mmap

mmap1.cpp

#include <sys/types.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>

#include <iostream>

int main() {
  int fd = open("./test_file", O_RDWR);

  if (fd == -1) {
    std::cerr << "Failed to open file. Abort." << std::endl;
    return -1;
  }

  char *buffer = new char[4096];
  const char *filler = "Hello!!\n";
  for (int i = 0; i < 4096; i += 8)
    for (int j = 0; j < 8; j ++)
      buffer[i + j] = filler[j];
  buffer[4095] = 0;

  write(fd, (const void *)buffer, 4096);
  delete [] buffer;

  buffer = (char *)mmap(NULL, 0x2000, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  std::cout << buffer << std::endl;
  buffer[0] = 'J';
  close(fd);

  return 0;
}