What does & stands for in C and mmap()

问题

int fd = open("/dev/mem", O_RDWR);
present = (unsigned char *)mmap(0, 
              getpagesize(), 
              PROT_READ|PROT_WRITE, 
              MAP_SHARED, 
              fd, 
              0x22400000);

if ((*present & 1) == 0)
{
  printf("Converter not present\n");
  exit(1);
}

1) What does '&' operator mean in the preceding code?

回答1:

It is the bitwise and operator. This means that the result of the operation is to perform binary and of the two operands but bit-by-bit (in a bitwise fashion i.e).

In this case it is checking that the first bit of the memory pointed to by present is 0.

来源：https://stackoverflow.com/questions/14928972/what-does-stands-for-in-c-and-mmap