Arduino上的strncmp_P和strncmp_PF之间的区别？

Question

What is the difference between strncmp_P and strncmp_PF on Arduino? I understand strncmp_F, but what is purpose of strncmp_PF?

Answer 1

There are two address spaces on Arduino: SRAM and Program memory (Flash).

You can refer to program memory using a normal "near" pointer, or a special "far" pointer to access more memory than is normally possible (eg near pointers can only access 64KB of program memory on a 16-bit CPU).

strncmp_P and strncmp_PF both compare with strings in program memory (as opposed to strncmp , which compares two strings from SRAM), but strncmp_PF takes a far pointer while strncmp_P takes a normal near pointer. That's the only difference.