What does this macro define?
I read this piece of macro(C code) and was confused in decoding it to know what it defines. What does it define?
#defin开发者_运维问答e sram (*((unsigned char (*)[1]) 0))
-AD
I think sram
means "start of RAM".
unsigned char[1]
An array of size 1 of unsigned chars.
unsigned char(*)[1]
A pointer to an array of size 1 of unsigned chars.
(unsigned char (*)[1]) 0
Cast 0 to a pointer to an array of size 1 of unsigned chars.
*((unsigned char (*)[1]) 0)
Read some memory at location 0, and interpret the result as an array of size 1 of unsigned chars.
(*((unsigned char (*)[1]) 0))
Just to avoid 1+5*8+1==42.
#define sram (*((unsigned char (*)[1]) 0))
Define the variable sram
to the memory starting at location 0, and interpret the result as an array of size 1 of unsigned chars.
I think it's returning the base address (0) of memory (RAM) :)
It defines "sram" as a pointer to memory starting at zero. You can access memory via the pointer, e.g. sram[0] is address zero, sram[1] is the stuff at address one, etc.
Specifically it is casting 0 to be a pointer to an array of unsigned char and going indirect through that (leaving an array of unsigned char).
A similar result can be obtained by
#define sram ((unsigned char*)0)
It is also completely undefined in standard C, but that doesn't stop people from using it and having angels fly out of their navels.
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