#define Command Problems

Hi,
Could you give me an explanation of below code, please?

1: #define M1 "Y X.2"
2: #define M2 (20000000L)
3: #define M3(p) *((unsigned char *)(& p))
4: #define M4(d,s) F1((d),(const char *)(s))
5: #define M5(d,s) F2((d),(const far rom char *)(s))
5: #define M6(t,n) typedef int n

Best, Thanks

You make no mention of what language it is or which assembler/compliler/editor or compositor it is for. I am assuming it is 'C':

#define just forces a text substitution where the pre-processor finds it. The '#defined' first parameter is expanded to the second and subsequent parameters.

1: substitutes the text "Y X.2" when you use M1
2: makes M2 equal to the long number 20000000
3: Makes M3(your value) expand to a pointer to the unsigned char cast to a pointer to (your value) address.
4: Makes M4(first value, second value) into whatever F1(first value),constant pointer to (second value) means. F1 must itself be defined somewhere else.
5: Same as 4 except this time the pointer is to rom and probably at a high address. It would be device dependant.
Second 5: A strange one but I assume M6 expands to 't' being the new typedef name and 'n' becoming a new int with name 'n'.

In short, the define is expanded so keyword are retained but parameters passed between ( and ) are substituted for their equivalent names within the definition.

Brian.

THANKS SO MUCH.

That's right, it is for C language.
I'm so sorry about my mistakes.
thanks again!