C stringification: convert constant to integer [closed] - c

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I need to convert defined constants to their integer values so I came up with this macro (STR_TO_CONST) for doing so...
#define STRFY_VAL(s) #s
#define STRFY_KEY(s) STRFY_VAL(s)
#define STR_TO_CONST(s) atoi(STRFY_KEY(s))
It works, but I'm wondering if there are any potential problems with it as I've never encountered this macro before despite having searched considerably for something like it.

Answer 1

The reason you never encountered this is that it's utterly pointless, but let's explain by example. Say you have the following:
#define FINALANSWER 42
// ...
int x = 2 * STR_TO_CONST(FINALANSWER);
now, this is semantically no different from:
int x = 2 * FINALANSWER;
That's because preprocessor macros are ultimately just textual replacement happening before you actually compile. Therefore, FINALANSWER is just as good as an integer constant as 42 is.
Your "solution" to a non-existing problem just adds overhead in that it adds a new string constant to your code and an unnecessary function call as well.

Answer 2

I'm wondering if there are any potential problems with it (?)
Yes. Using atoi() to initialize a global results in something like "error: initializer element is not constant"
int x = STR_TO_CONST(123); // error
int y = 123; // no error
int main(void) {
return x + y;
}
Hide warnings. Only 1 line generated a useful warning
"warning: overflow in implicit constant conversion [-Woverflow]"
int main(void) {
int a = STR_TO_CONST(123456789012345); // no warning
int b = 123456789012345; // warning
return a + b;
}
Range issue. With 32-bit int, the below will likely exceed atoi() range resulting in undefined behavior with no warning.
int main(void) {
long long z = STR_TO_CONST(123456789012345);
return !z;
}