#define SATA_PORT_0 "/sata-ahci/port0"
#define SATA_PORT_1 "/sata-ahci/port1"
#define SATA_PORT_2 "/sata-ahci/port2"
#define SATA_PORT_3 "/sata-ahci/port3"
#define SATA_PORT_4 "/sata-ahci/port4"
#define SATA_PORT_5 "/sata-ahci/port5"
#define SATA_NODE(p) HOW TO DEFINE THIS?!!
int main()
{
int i;
for (i=0;i<6;i++)
{
printf("%s\n", i, SATA_NODE(i));
}
return 0;
}
Question: how to define above macro, to get string print out in GCC ?
You can't readily do it with a macro.
The problem is that a macro is a compile time construct, and the loop you have there is a run time construct; you can't do it directly.
You could investigate Boost Preprocessor (which is not specifically for C++; it also works with the C preprocessor) and use that to write macros which generate the loop.
You could hand unroll the loop and use a macro with a constant argument:
#define SATA_PORT(i) "/sata-ahci/port" #i
printf("%s\n", 0, SATA_PORT(0));
printf("%s\n", 1, SATA_PORT(1));
printf("%s\n", 2, SATA_PORT(2));
printf("%s\n", 3, SATA_PORT(3));
printf("%s\n", 4, SATA_PORT(4));
printf("%s\n", 5, SATA_PORT(5));
Or you can use an array of strings (also suggested by a now-deleted answer).
#define DIM(x) (sizeof(x)/sizeof(*(x)))
const char * const sata_ports[] =
{
"/sata-ahci/port0",
"/sata-ahci/port1",
"/sata-ahci/port2",
"/sata-ahci/port3",
"/sata-ahci/port4",
"/sata-ahci/port5"
};
for (int i = 0; i < DIM(sata_ports); i++)
printf("%d %s\n", i, sata_ports[i]);
In the C language you can't. Macro substitution occurs before ordinary compilation. The preprocessor doesn't know that preprocessing token i is going to be declared as an int later during ordinary compilation.
Execution comes even later. The compiler can figure out that i is going to have values ranging from 0 to 5, but that doesn't help you. The actual assignments occur during execution, which is after compilation finished, which is after preprocessing finished.
Thanks for above answers. I found a way to do this myself.
#define SATA_PORT(p) (p==0)?SATA_PORT_0:ISP1
#define ISP1 (p==1)?SATA_PORT_1:ISP2
...
In some situations, the above macro makes the code much better.
EDIT: I've made solution a little bit nicer (because of availability of compound statements in GCC compiler).
If i had similar problem I would solve it like this:
#define SATA_PORT(p) ({char prt[100]; sprintf(prt, "/sata-ahci/port%d", p); prt;})
And BTW you forgot printf format specifier for variable i.
Maybe this is what you need(ed):
#define STRINGIFY(x) #x
#define TOSTRING(x) STRINGIFY(x)
#define SATA_NODE_TO_SATA_PORT(p) SATA_PORT_##p
#define SATA_NODE(p) TOSTRING(SATA_NODE_TO_SATA_PORT(p))
Then, if you try to print the preprocessed macros with:
std::cout << SATA_NODE(3) << " - " << SATA_NODE(5) << std::endl;
std::cout << SATA_NODE(7) << std::endl;
what you get is:
"/sata-ahci/port3" - "/sata-ahci/port5"
SATA_PORT_7
