xdata access by #define

"the "problems" experienced in the cited threads both relate to a proper understanding of the Compiler's internal data representation - or lack thereof!

Thanks for clarifying. I figured my point didn't come across. Yes those threads do relate to internal representation. However, yy cautions are independent of the implementation -- strictly a "C thing". The context in which XBYTE and XWORD are used expect "array-ness", if you will, and this is a particular problem with XWORD, regardless of the target system. XBYTE[data2] accesses a byte at address 0x0100, whereas XWORD[data2] accesses a word at address 0x0200.

I personally find the dichotomy awkward and a source of errors. When I'm thinking in terms of addresses, I want my macros to implement them as addresses/pointers, not arrays where one macro coincidentally works with addresses and the other does not. I prefer something a bit more generic, allowing me to always use addresses pointing to anything. A contrived example:

// data locations
#define data1 0
#define data2 data1+0x100

#define XDAT(type, addr)    (*(type xdata *)(addr))

struct FOO
{
    long l[3];
    char c;
};

unsigned char b;
unsigned int  w;
unsigned long l;

void main(void)
{
    b = XDAT(unsigned char, data2);
    w = XDAT(unsigned int,  data2);
    l = XDAT(unsigned long, data2);

    b = XDAT(struct FOO, data2).c;
}

"the "problems" experienced in the cited threads both relate to a proper understanding of the Compiler's internal data representation - or lack thereof!

Thanks for clarifying. I figured my point didn't come across. Yes those threads do relate to internal representation. However, yy cautions are independent of the implementation -- strictly a "C thing". The context in which XBYTE and XWORD are used expect "array-ness", if you will, and this is a particular problem with XWORD, regardless of the target system. XBYTE[data2] accesses a byte at address 0x0100, whereas XWORD[data2] accesses a word at address 0x0200.

I personally find the dichotomy awkward and a source of errors. When I'm thinking in terms of addresses, I want my macros to implement them as addresses/pointers, not arrays where one macro coincidentally works with addresses and the other does not. I prefer something a bit more generic, allowing me to always use addresses pointing to anything. A contrived example:

// data locations
#define data1 0
#define data2 data1+0x100

#define XDAT(type, addr)    (*(type xdata *)(addr))

struct FOO
{
    long l[3];
    char c;
};

unsigned char b;
unsigned int  w;
unsigned long l;

void main(void)
{
    b = XDAT(unsigned char, data2);
    w = XDAT(unsigned int,  data2);
    l = XDAT(unsigned long, data2);

    b = XDAT(struct FOO, data2).c;
}