Problems using boost multiprecision library

Question

I am trying to write a base conversion program that will work for numbers beyond the limits of C++'s long long integers. I am trying to use boost multiprecision libraries but have not made it very far.

I have tried to compile the following:

#include <boost/multiprecision/gmp.hpp>
#include <iostream>
#include <string>
#include <stdio.h>

namespace boost{ namespace multiprecision{

class gmp_int;

typedef number<gmp_int >         mpz_int;

}} // namespaces
 using namespace boost::multiprecision;
int main(int argc, const char * argv[]) {
mpz_int seed = 18446744073709551615;

 std::cout << seed;
  return 0;
}

and received the following errors:

    main.cpp:17:20: error: reference to 'gmp_int' is ambiguous
typedef number<gmp_int >         mpz_int;
               ^


main.cpp:15:11: note: candidate found by name lookup is
  'boost::multiprecision::gmp_int'
class gmp_int;
      ^

/usr/local/boost_1_57_0/boost/multiprecision/gmp.hpp:2157:40: note:      candidate
  found by name lookup is 'boost::multiprecision::gmp_int'
using boost::multiprecision::backends::gmp_int;
                                   ^

main.cpp:17:20: error: reference to 'gmp_int' is ambiguous
typedef number<gmp_int >         mpz_int;
               ^

main.cpp:15:11: note: candidate found by name lookup is
  'boost::multiprecision::gmp_int'
class gmp_int;
      ^

 /usr/local/boost_1_57_0/boost/multiprecision/gmp.hpp:2157:40: note: candidate
  found by name lookup is 'boost::multiprecision::gmp_int'
using boost::multiprecision::backends::gmp_int;
                                   ^

main.cpp:17:38: error: typedef redefinition with different types ('number<class
  boost::multiprecision::gmp_int>' vs 'number<struct
  boost::multiprecision::backends::gmp_int>')
typedef number<gmp_int >         mpz_int;
                                 ^

/usr/local/boost_1_57_0/boost/multiprecision/gmp.hpp:2214:34: note: previous
  definition is here
typedef number<gmp_int >         mpz_int;
                             ^

main.cpp:22:2: error: reference to 'gmp_int' is ambiguous
 gmp_int seed = 18446744073709551615;
 ^

/usr/local/boost_1_57_0/boost/multiprecision/gmp.hpp:2157:40: note: candidate
  found by name lookup is 'boost::multiprecision::gmp_int'
using boost::multiprecision::backends::gmp_int;
                                   ^

main.cpp:15:11: note: candidate found by name lookup is
    'boost::multiprecision::gmp_int'
class gmp_int;
      ^

main.cpp:32:18: error: use of undeclared identifier 'seed' std::cout << seed; ^ 5 errors generated.

I know I must be making some pretty basic mistakes but I haven't had any success in fixing them. any help would be appreciated.

I got a simple program to work using #include <boost/lambda/lambda.hpp>, so I am fairly certain that boost is installed correctly.

Answer 1

You are declaring a new type class gmp_int;. I cannot fathom any reason why you would want to do so.

However, this means that the next line

typedef number<gmp_int >         mpz_int;

now is unable to decide whether you mean your new type ::gmp_int or Boosts version ::boost::multiprecision::gmp_int.

Your C++ compiler is attempting to tell you that it cannot decide which gmp_int is meant with its message "reference to 'gmp_int' is ambiguous".

Answer 2

It looks like you copied the wrong bits from the documentation: http://www.boost.org/doc/libs/1_57_0/libs/multiprecision/doc/html/boost_multiprecision/tut/ints/gmp_int.html

What's shown is a reference summary, not a usage synopsis. The types shown already exist.

A clear case of less is more:

Live On Coliru

#include <boost/multiprecision/mpfr.hpp>
#include <iostream>

int main() {
    boost::multiprecision::mpz_int seed = 18446744073709551615ull;
    std::cout << seed;
}