how to find the value of a macro?

[George2]

Hello everyone,


I am wondering what is the easiest and safest way to find the value of a macro? For example, if I,

#define FOO "value1"

The value of FOO I can get is "value1" and if then I,

#undef FOO
#define FOO "value2",

then the value of FOO I can get is "value2".


thanks in advance,
George

[Salem]

You get the value by using the name
Eg.
printf( "Foo is %s", FOO );

There is no way to determine if FOO will make sense in the context in which you use it.
Eg.
#define FOO 123
printf( "Foo is %s", FOO ); // may get a warning, may blow up at run-time

[itsme86]

Something like this would avoid that potential problem:

itsme@itsme:~/C$ cat macro.c
#include <stdio.h>

#define FOO 123
#define BAR "blee"

#define STR2(x) #x
#define STR(x) STR2(x)

int main(void)
{
  printf("FOO: %s\n", STR(FOO));
  printf("BAR: %s\n", STR(BAR));

  return 0;
}

itsme@itsme:~/C$ ./macro
FOO: 123
BAR: "blee"
itsme@itsme:~/C$

The above code allows you to print non-string macros just like you'd print string macros.

[Cactus_Hugger]

If your compiler supports it, set it to preprocess only, and see what the macro is replaced with.

C:\Roys\Projects\cboard>cat hello.c
#include <stdio.h>

#define HI "Hello World!\n"

int main()
{
        printf(HI);
        return 0;
}

C:\...\Projects\cboard>gcc hello.c -E
<snip>
int main()
{
 printf("Hello World!\n");
 return 0;
}

Always more than one way to do things.