CODEWITHSUNDEEP
c++gmp
Nasst
Nasst

Reputation: 13

Casting an mpz_class temporary to int

As part of my code's logic, I'm assigning the result of an expression involving mpz_class to an int. The problem is, mpz_class overloaded operators don't seem to produce mpz_class objects, but rather, some kind of temporaty object that then gets converted to mpz_class (if I understood this correctly). Because of this Is there any way that I can convert the result of bignum % 10 to an int inline?

int digit_sum = 0;
while(bignum > 0) {
    digit_sum += bignum % 10;
    bignum /= 10;
}

Upvotes: 1

Views: 244

Answers (1)

L. F.
L. F.

Reputation: 20569

The GMP library uses expression templates to avoid unnecessary temporary variables. As such, bignum % 10 returns a proxy that represents the expression and only evaluates when converted to mpz_class. Also, mpz_class does not implicitly convert to int. Therefore, as mentioned in comment, you need to first convert to mpz_class and then use the get_si method to convert the mpz_class to long.

digit_sum += mpz_class{bignum % 10}.get_si();

Note that in general, you need to make sure that the number actually fits into long before calling get_si. In this case, the (absolute) number is always less than 10, so it is safe to call get_si.

Upvotes: 1

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