Define function in macros (in C)

Question

I need to #define a macros as a function. For example:

#define REGISTER 0x80000000
...
writel(addr, nic->regs + REGISTER); // arguments are address and register

I defined it like that:

#define WRITEL(addr, nic->reg + reg) ((writel(addr, nic->regs + (reg))))

What's wrong here? Thanks

Do you have a paticular reason to do it as a macro, not the normal function with all the benefits (type checking ...... etc etc)? — 0___________
– 0___________, Commented Jul 14, 2017 at 10:36

JeremyP · Accepted Answer · 2017-07-14 10:51:56Z

7

Macro arguments are a bit like normal function arguments. On the left side you just need a name that is used on the right

 #define WRITEL(ADDR, REG) (writel(ADDR, nic->regs + (REG)))

answered Jul 14, 2017 at 10:19

JeremyP

87.3k15 gold badges129 silver badges164 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Thank you! Never did these things. I think I got the principle. I really appreciate your help

But is it necessary to cover the function with () ?

@GeorgeZ. it is not.

Sorry @tilz0R is correct. It was muscle memory. Any other expression than a single bare function call would require the parentheses.

@tilz0R That's a good point. Keeping the parentheses is defensive.

|