[Moved] how to change avalue of macro during execution?

[A.Rashad]

Is there any means to change value of a macro depending on some execution during run time ?

e.g #define VALUE A

now I want this A to get different values during code execution ,
say in main ()
A=x+y;
A can be different values based on x or y, how can I assign Value of this variable to macro VALUE ?

 

[mrflibble]

Re: how to change avalue of macro during execution?

AFAIK macros are compile time, not run time. So no, that's not possible. But you can obviously use a function or variable to take care of all your runtime needs.

 

[xtcx]

Re: how to change avalue of macro during execution?

Maybe you should try asking in Microcontroller forums....

 

[mrflibble]

Re: how to change avalue of macro during execution?

He could ask in the gcc mailing list, answer is still going to be no.

 

[std_match]

Re: how to change avalue of macro during execution?

It will work if A is a variable. "VALUE" will be replaced with "A" early at compile time, so all references to "VALUE" will use the number stored in variable A.

Normally a macro is used to set a constant value like this:
#define VALUE 32

A macro in C is just a text substitution done at compile time, so a fixed number is not necessary.
A variable name will work:

---

Code C - [expand]
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#define VALUE A
int A;
....
A = x + y;
if(VALUE > 123){
  printf("Above 123\n");
}
....

---

The compiled code will look like this:

---

Code C - [expand]
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int A;
...
A = x + y;
if(A > 123){
  printf("Above 123\n");
}
....

---

As shown, the variable "A" can be declared after the #define since it is just a text string in the #define.
"A" must be declared before the macro VALUE is used.

 

[xtcx]

I wonder how you guys learn HDL and also C togethor and yet live without confusion. I have not learnt C myself yet much, but still just finding it tough than learning HDL,