Hello,
I read this piece of macro(C code) and was confused in decoding it to know what it defines. What does it define?
#define sram (*((unsigned char (*)[1]) 0))
-AD
+1
A:
I think it's returning the base address (0) of memory (RAM) :)
John Weldon
2010-02-23 18:04:58
+11
A:
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.
KennyTM
2010-02-23 18:07:52
+1 for providing me with an explanation to that conundrum in the Hitchhiker's Guide five-part trilogy. Oh, and I guess the rest of your answer was okay too.
Platinum Azure
2010-02-23 18:24:54
Or on an embedded system it could just mean "SRAM" (Static Random Access Memory) which is typically what a microcontroller's on-chip RAM is made of.
Clifford
2010-02-23 18:40:22
+1
A:
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.
Richard Pennington
2010-02-23 18:07:53