getting the variable values in #define definition

Question

Here is what I am trying to do.

step1) I want to call a macro with a conditional statement(simple are compounded) like

for eg:

 MACRO1(a==1)
 MACRO1((i!=NULL) && (j>10))

step2) Here is how i am defining this macro

#define MACRO1(condition) \
        if(!(condition)) ??????????????????????????

Here in the definition of the macro, if the condition statement fails. I want to print the variable values so that I will be useful to know the exact reason. I used #condition in the definition, but it just printing the condition, instead of the values of the variables used in the condition. Please help.

Answer 1

You could do something along these lines:

#define MACRO1(condition, msg) \
    if(!(condition)) { printf msg; }

and use it as follows:

MACRO1(a==1, ("a: %d\n", a))
MACRO1((i != NULL) && (j>10), ("i: %p, j: %d\n", i, j));

The C preprocessor is just a simple substitution engine, without the capability of analyzing the contents of expressions.