Insert variable value into a variable name in C

Question

I have a type defined e.g.:

typedef enum {
 T1,
 T2,
 T3,
 T4,
 T5,
 T6,
 LAST_IN_ENUM
} type1_t;

then another one using the above type e.g.:

typedef enum {
 SUB1 = T1,
 SUB2 = T2,
 SUB3 = T3,
 SUB4 = T4
} type2_t;

I would like to use then some fields of type2_t as input parameters to a function, but referring to its last character from a loop variable value, e.g. for SUB2 and SUB3:

for (i=2; i<4; i++) {
 function1(SUBi)
}

What I don't know what the proper syntax is to pass the loop variable value to make it up SUBx (the above for loop syntax doe snot work, obviously).

Thanks a lot in advance if you have the solution.

I tried casting, converting to string, none of them worked.

Try for( i = SUB2; i < SUB4; i++ ) The enum tokens are no more that compile time tokens that represent integer values. They are not runtime variables for accessing or manipulating. — user17592432
– user17592432, Commented Jan 13, 2023 at 10:50
I don't think you can construct a variable on-the-fly in this way in C. You could just create an array with the appropriate SUB values in the corresponding index location within the array. — Matt Pitkin
– Matt Pitkin, Commented Jan 13, 2023 at 10:51
Take a look at this: stackoverflow.com/questions/16844728/… — Fabio_MO
– Fabio_MO, Commented Jan 13, 2023 at 10:53
Thanks for the answers. It seems inserting the loop variable value into the enum is not possible. — Lorinc
– Lorinc, Commented Jan 13, 2023 at 12:18

0___________ · Accepted Answer · 2023-01-13 10:52:10Z

0

You cant, I am afraid

You can only (if values are consecutive):

void bar(type2_t t2);

void foo(void)
{
    for(type2_t t = SUB1; t <= SUB4; t++)
    {
        bar(t);
    }
}

Or if they are not:

typedef enum {
 T1 = 5,
 T2 = 35,
 T3 = 65,
 T4 = 999,
 T5,
 T6,
 LAST_IN_ENUM
} type1_t;

typedef enum {
 SUB1 = T1,
 SUB2 = T2,
 SUB3 = T3,
 SUB4 = T4
} type2_t;

void bar(type2_t t2);

void foo(void)
{
    const type2_t t2Table[] = {SUB1, SUB2, SUB3, SUB4};
    for(size_t t = 0; t < sizeof(t2Table) / sizeof(t2Table[0]); t++)
    {
        bar(t2Table[t]);
    }
}

answered Jan 13, 2023 at 10:52

0___________

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1 Comment

Lorinc Over a year ago

Thanks, the 2nd solution is closer already what I need, it seems that the way that seemed to be the most useful (inserting the value of the loop variable) is not possible unfortunately.

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