Is there a C++ equivalent to Java's BigDecimal?

Question

I\'m looking for a C++ class that can do decimal floating point arithmetic. Looking through http://speleotrove.com/decimal/ there are links to all sorts of classes that peop

Answer 1

Probably "MAPM, A Portable Arbitrary Precision Math Library in C" is what you are looking for. It also includes C++ Wrappers:

http://www.tc.umn.edu/~ringx004/mapm-main.html

Answer 2

Take your pick. There are a bunch of them out there. For instance, you can consult the list on Wikipedia.

Answer 3

Use GMP and store everything as cents. If you know that you won't pass 2^32 cents (42.949673 million dollars) use a 32 bit unsigned int (or use a 64 bit unsigned int) and keep it simple.

Answer 4

I may be too late for this but would 128bit decimals work? These have been accepted into C++ and at least gcc has them since gcc-4.5 (we're starting 4.9 now:

#include <iostream>
#include <decimal/decimal>

using namespace std;

int main()
{
  {
    std::decimal::decimal32 dn(.3), dn2(.099), dn3(1000), dn4(201);
    dn-=dn2;
    dn*=dn3;
    cout << "decimal32 = "  << (dn==dn4) << " : " << decimal32_to_double(dn) << endl;
  }

  {
    std::decimal::decimal64 dn(.3), dn2(.099), dn3(1000), dn4(201);
    dn-=dn2;
    dn*=dn3;
    cout << "decimal64 = "  << (dn==dn4) << " : " << decimal64_to_double(dn) << endl;
  }

  {
    std::decimal::decimal128 dn(.3), dn2(.099), dn3(1000), dn4(201);
    dn-=dn2;
    dn*=dn3;
    cout << "decimal128 = " << (dn==dn4) << " : " << decimal128_to_double(dn) << endl;
  }

  return 0;
}

Note there is decimal32 equal in size to float, decimal64 equal in size to most double. So decimal128 is pretty big. From Wikipedia: Decimal128 supports 34 decimal digits of significand and an exponent range of −6143 to +6144, i.e. ±0.000000000000000000000000000000000×10−6143 to ±9.999999999999999999999999999999999×106144. (Equivalently, ±0000000000000000000000000000000000×10−6176 to ±9999999999999999999999999999999999×106111.)

The mpfr library is arbitrary precision binary floating point - not arbitrary precision decimal. There is a difference.

Answer 5

The question is a bit old, but for other people that have the same need : Boost.multiprecision is probably what you're looking for.

http://www.boost.org/doc/libs/1_57_0/libs/multiprecision/doc/html/boost_multiprecision/tut/floats/cpp_dec_float.html

It's an arbitrary precision library that can handle 10-based decimals.

Answer 6

There exists a huge library called GMP (GNU multiple precision library) which supports this and also has C++ bindings, though to be honest the C++ interface is a bit wonky and outdated.

An example from the documentation, the following creates a float called f with at least 500 bits of precision:

mpf_class f(1.5, 500);