How can I set a NanoPi Neo's PIO as output on hardware level in C++?

As per the Allwinner H3 Datasheet the following hardware addresses are specified:

PIO Base Address: 0x01C20800 (p. 316)

PG Configure Register 1 offset: 0xDC (p. 338)

PG11 bits: 14:12 (p. 338)

  struct peripheral {
      unsigned long addr_hardware;
      int map_size;
      int mem_fd;
      void *mem_map;
      volatile unsigned long *addr_virtual;

      int map() {
          if ((mem_fd = open("/dev/mem", O_RDWR | O_SYNC)) < 0) return -1;
          // map addr_hardware=0x01C20000 into /dev/mem
          if ((mem_map = mmap(0, map_size, PROT_READ | PROT_WRITE, MAP_SHARED, mem_fd, addr_hardware)) == MAP_FAILED) return -1;
          // store virtual address with offset of 0x800, which was rounded down before
          addr_virtual = (volatile unsigned long *) mem_map + 0x800;
          return 0;
      };
      void unmap() {
          munmap(mem_map, map_size);
          close(mem_fd);
      };
  };

  int main() {
      // initialize peripheral at rounded down PIO base address
      peripheral gpio {0x01C20000, 4096 * 10};
      // map PIOs into virtual memory
      if (gpio.map() == -1) return -1;

      // output current value of PG Configure Register 1
      cout << bitset<32>(*(gpio.addr_virtual + 0xDC)) << endl;
      // set 12th bit
      *(gpio.addr_virtual + 0xDC) |= (1 << 12);
      // output value of register after setting the 12th bit
      cout << bitset<32>(*(gpio.addr_virtual + 0xDC)) << endl;

      gpio.unmap();
      return 0;
  }

Any help would be very appreciated