Function-like macro and enumerator with the same name

Question

In the following fragment I have a struct IndexError that I return when the user made an error using my library. I have a function-like macro that casts a pointer to a IndexError*, and an enum, both called INDEX_ERROR.

enum errors {
    SUCCESS,
    INVALID_ARGUMENT,
    INDEX_ERROR
};

struct Error {
    char error_buff[BUFSIZ];
};

typedef struct Error Error;

struct IndexError {
    Error  parent;
    size_t invalid_index;
    // etc.
};

typedef struct IndexError IndexError;


#define INDEX_ERROR(obj) ((IndexError*) obj)

An example to how I would use this is:

size_t pos = 4;
int IndexPointer* error = NULL;
int status = array_remove_item(my_array, pos, &error);

Then I check the status. If it doesn't return SUCCESS, I would examine the error, because that should then point to a newly create error.

The implementation of one of the array functions might look like this:

int array_remove_item(Array* array, size_t pos, Error** error_out)
{
    Error* error = NULL;
    if(pos >= array->size) {
        index_error_create(INDEX_ERROR(&error), pos); // use casting macro.
        *error_out = error;
        return INDEX_ERROR; // is this the macro or the value from the errors enum?
    }
    priv_array_remove_item(array, pos);
    return SUCCESS;
}

So my question is, at the return INDEX_ERROR;, will the INDEX_ERROR return the value from the enum, or will the preprocessor bite me because my naming is inconvenient?

Answer 1

return INDEX_ERROR; // is this the macro or the value from the errors enum?

It's the enumerator. It can't be the result of expanding the function-like macro, because it isn't followed immediately by a left paren ( token, as the preprocessor requires¹.

It's slightly smelly, though. Different names for the macro and the enumerator will make the code clearer and self evident without needing to read the fine print of the language specification.

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_{¹ - n1570 6.10.3p10 "Each subsequent instance of the function-like macro name followed by a ( as the next preprocessing token introduces the sequence of preprocessing tokens that is replaced by the replacement list in the definition"}