Geek Answers Handbook

Can I do something like #define ARRAY (size) char [## size ##] in C?

I am trying to define a macro to create a structure in my global scope, for example, the code above:

#define BUFFER(size) \
struct { \
    unsigned short size = ##size; \
    unsigned short readIndex = 0; \
    unsigned short writeIndex = 0; \
    unsigned char dataPtr[##size##]; \
}

BUFFER(10) buffer10bytes;
BUFFER(50) buffer50bytes;

The problem is that gcc does not evaluate this macro. Can I archive? How?

Here is my compiler error:

In file included from ../usart.c:12:0:
../usart.c:14:8: error: expected identifier or '(' before numeric constant
 BUFFER(10) buffer10bytes;
        ^
../buff.h:24:17: note: in definition of macro 'BUFFER'
  unsigned short size = ##size; \
                 ^
../buff.h:24:22: error: pasting "=" and "10" does not give a valid preprocessing token
  unsigned short size = ##size; \
                      ^
../usart.c:14:1: note: in expansion of macro 'BUFFER'
 BUFFER(10) buffer10bytes;
 ^
../buff.h:25:27: error: expected ':', ',', ';', '}' or '__attribute__' before '=' token
  unsigned short readIndex = 0; \
                           ^
../usart.c:14:1: note: in expansion of macro 'BUFFER'
 BUFFER(10) buffer10bytes;
 ^
../buff.h:27:23: error: pasting "[" and "10" does not give a valid preprocessing token
  unsigned char dataPtr[##size##]; \
                       ^
../usart.c:14:1: note: in expansion of macro 'BUFFER'
 BUFFER(10) buffer10bytes;
 ^
../usart.c:14:8: error: pasting "10" and "]" does not give a valid preprocessing token
 BUFFER(10) buffer10bytes;
        ^
../buff.h:27:26: note: in definition of macro 'BUFFER'
  unsigned char dataPtr[##size##]; \
                          ^
../usart.c:15:8: error: expected identifier or '(' before numeric constant
 BUFFER(50) buffer50bytes;
        ^
../buff.h:24:17: note: in definition of macro 'BUFFER'
  unsigned short size = ##size; \
                 ^
../buff.h:24:22: error: pasting "=" and "50" does not give a valid preprocessing token
  unsigned short size = ##size; \
                      ^
../usart.c:15:1: note: in expansion of macro 'BUFFER'
 BUFFER(50) buffer50bytes;
 ^
../buff.h:25:27: error: expected ':', ',', ';', '}' or '__attribute__' before '=' token
  unsigned short readIndex = 0; \
                           ^
../usart.c:15:1: note: in expansion of macro 'BUFFER'
 BUFFER(50) buffer50bytes;
 ^
../buff.h:27:23: error: pasting "[" and "50" does not give a valid preprocessing token
  unsigned char dataPtr[##size##]; \
                       ^
../usart.c:15:1: note: in expansion of macro 'BUFFER'
 BUFFER(50) buffer50bytes;
 ^
../usart.c:15:8: error: pasting "50" and "]" does not give a valid preprocessing token
 BUFFER(50) buffer50bytes;
        ^
../buff.h:27:26: note: in definition of macro 'BUFFER'
  unsigned char dataPtr[##size##]; \
                          ^
make: ** [usart.o] Erro 1
+4
source share
1 answer

Take out ##. This is to create a new token from two tokens; but you are not doing it here, you really just want two tokens.

Also, you cannot use the same name for a variable as for a macro parameter.

, . , :

#define DECLARE_BUFFER(size_, name) \
struct { \
    unsigned short readIndex;
    unsigned short writeIndex;
    unsigned char dataPtr[size_]; \
} name = { 0 }

BUFFER(10, buffer10bytes);
BUFFER(50, buffer50bytes);

size, : sizeof X.dataPtr, . (: Ptr - ). size, ( Remy ), , - :

#define DECLARE_BUFFER(size_, name) \
struct { \
    unsigned short size;
    unsigned short readIndex;
    unsigned short writeIndex;
    unsigned char dataPtr[size_]; \
} name = { size_, 0 }
+8

More articles:


All Articles