#include <stddef.h>
 
#define C_ASSERT(expr) extern char CAssertExtern[(expr)?1:-1]
 
// You keep this definition private to module A (e.g. in a .c file):
typedef struct
{
    int A;
    int B;
    int C[4];
} PrivateStruct;
 
// You expose this definition to all modules (in an .h file):
typedef struct
{
    char reserved[2*sizeof(int)];
    int C[4];
} PublicStruct;
 
// You put these in module A (in a .c file):
C_ASSERT(sizeof(PrivateStruct) == sizeof(PublicStruct));
C_ASSERT(offsetof(PrivateStruct,C) == offsetof(PublicStruct,C));
 
int main(void)
{
  return 0;
}
 

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