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#### gmp_int

`#include <boost/multiprecision/gmp.hpp>`

    namespace boost{ namespace multiprecision{

    class gmp_int;

    typedef number<gmp_int >         mpz_int;

    }} // namespaces

The `gmp_int` back-end is used via the typedef `boost::multiprecision::mpz_int`. It acts as a thin wrapper around the GMP `mpz_t` to provide an integer type that is a drop-in replacement for the native C++ integer types, but with unlimited precision.

As well as the usual conversions from arithmetic and string types, type `mpz_int` is copy constructible and assignable from:

- The GMP native types: `mpf_t`, `mpz_t`, `mpq_t`.
- Instances of `number<T>` that are wrappers around those types: `number<gmp_float<N> >`, `number<gmp_rational>`.

It's also possible to access the underlying `mpz_t` via the `data()` member function of `gmp_int`.

Things you should know when using this type:

- No changes are made to the GMP library's global settings - so you can safely mix this type with existing code that uses GMP.
- Default constructed `gmp_int`s have the value zero (this is GMP's default behavior).
- Formatted IO for this type does not support octal or hexadecimal notation for negative values, as a result performing formatted output on this type when the argument is negative and either of the flags `std::ios_base::oct` or `std::ios_base::hex` are set, will result in a `std::runtime_error` will be thrown.
- Conversion from a string results in a `std::runtime_error` being thrown if the string can not be interpreted as a valid integer.
- Division by zero results in a `std::overflow_error` being thrown.
- Although this type is a wrapper around GMP it will work equally well with MPIR. Indeed use of MPIR is recommended on Win32.
- This backend supports rvalue-references and is move-aware, making instantiations of `number` on this backend move aware.

###### Example:

    #include <boost/multiprecision/gmp.hpp>

    using namespace boost::multiprecision;

    mpz_int v = 1;

    // Do some arithmetic:
    for(unsigned i = 1; i <= 1000; ++i)
       v *= i;

    std::cout << v << std::endl; // prints 1000!

    // Access the underlying representation:
    mpz_t z;
    mpz_init(z);
    mpz_set(z, v.backend().data());