CODEWITHSUNDEEP
cmacros
Chan Kim
Chan Kim

Reputation: 5929

how to substitute function using macro in C

Sometimes, in a C code I borrowed from a linux driver, I want to change some macros into a function that I can use in my environment. But this previous macro can take 3 or 4 arguments.
For example, if I want to substite 

SMSC_TRACE(pdata, probe, "Driver Parameters:");   // 3 arguments

into 

printf("Driver Parameters:");

and substitute 

SMSC_TRACE(pdata, probe, "LAN base: 0x%08lX", (unsigned long)pdata->ioaddr); // 4 arguments

into 

printf("LAN base: 0x%08lX", (unsigned long)pdata->ioaddr);

How do I do that? I tried

#define SMSC_TRACE((a), (b), (c)) printf((c))  
#define SMSC_TRACE((a), (b), (c), (d)) printf((c), (d))

but it doesn't seem to work. Only the last one seems to take effect.

EDIT: this seems it maybe.

#define SMSC_TRACE(pdata, nlevel, fmt, args...) printf(fmt "\n", ##args)

Upvotes: 2

Views: 405

Answers (1)

barak manos
barak manos

Reputation: 30136

You can do it with a variadic macro, which takes a variable number of arguments:

#define SMSC_TRACE(a,b,...) printf(__VA_ARGS__)

If you want this macro to execute multiple statements, then you need a do/while(0).

For example:

#define SMSC_TRACE(a,b,...) \
do                          \
{                           \
    printf("%c\n",a);       \
    printf("%d\n",b);       \
    printf(__VA_ARGS__);    \
}                           \
while (0)

Upvotes: 5

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