How to initialize a GMP mpz_t with an integer

Question

I want to initialize a mpz_t from GMP with an integer (e.g. 2). I've tried the following variants:

mpz_t n(2); // Compiler error
mpz_t n = 2; // Compiler error

What is the correct way of initializing the mpz_t to 2?

I think you are looking for the type `mpz_class` (from gmpxx.h), not the low-level C mpz_t type. — Marc Glisse, Jan 21 '18 at 19:31
@MarcGlisse Yes, it would be easier using that. However `gmpxx` is a separate package to install and I wanted to do a problem-solution post on the raw `mpz_t` because some people are likely to run into that problem. — Uli Köhler, Jan 21 '18 at 20:22

Uli Köhler · Accepted Answer · 2018-01-21T20:19:31.663

4

mpz_t n;
mpz_init_set_ui(n); // ui means unsigned int. Use si for signed values.

Thanks to Mark Glisse for mentioning combined init & set.

edited Jan 21 '18 at 20:19

answered Jan 21 '18 at 18:49

Uli Köhler

You can also merge the last 2 lines. – Marc Glisse Jan 21 '18 at 19:32
@MarcGlisse Thanks, I wasn't aware of that actually ;-) I have edited the answer accordingly – Uli Köhler Jan 21 '18 at 20:20

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