How to store a very large number in c++

Question

Is there any way to store a 1000 digit number in c++? I tried storing it to an unsigned long double but it is still to large for its type.

I doubt you could put anything inside a "unsigned long double"... — dtech, Apr 23 '15 at 01:34
Another thought occurs - what is your 1000 digit number data source? Is it by chance a literal? — dtech, Apr 23 '15 at 01:47
Well, it won't work, C++ doesn't support literals of such size. IIRC big number libs usually input the numbers as strings rather than number literals. — dtech, Apr 23 '15 at 02:19

score 4 · Accepted Answer · edited May 23 '17 at 12:32

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You may find your answer here How to store extremely large numbers? GMP answer sounds right, ie this is what it does with pi digits https://gmplib.org/pi-with-gmp.html

edited May 23 '17 at 12:32

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answered Apr 23 '15 at 00:23

sed

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Is GMP not included in c++ standard libraries? – wazalak Apr 23 '15 at 00:37
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doesn't seem like it, but you may download it there and load it into your project, see here to get help with it http://stackoverflow.com/questions/10358745/how-to-use-libraries – sed Apr 23 '15 at 00:58

score 1 · Answer 2 · answered Apr 23 '15 at 00:24

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You have to implement it yourself or use a library for it. In particular I love GMP: https://gmplib.org/ , which is an C implementation of Big Int/Float and has C++ wrapper

answered Apr 23 '15 at 00:24

MasterID

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score 1 · Answer 3 · answered Apr 23 '15 at 01:16

Use a custom class for your number, something like this:

#include <vector>
#include <iostream>

    class large_num {
     private:
        int digits;    // The number of digits in the large number
        std::vector<int> num;    // The array with digits of the number.
     public:
        // Implement the constructor, destructor, helper functions etc.
    }

For a very large number just add each digit to the vector. For example if the number if 123456, then you do num.pushback(); In this case push all the digits 1,2, .. 6. You can store a extremely large numbers this way.

That's not a bad approach for people learning C++, as a bit of a project, but a couple nit-picks: `num` has a `.size()` facility already so `digits` is redundant and another thing that could get out of sync, and a `std::vector` or similar (even a `std::string`) would use a lot less memory. — Tony Delroy, Apr 23 '15 at 03:47

score 0 · Answer 4 · answered Apr 23 '15 at 00:22

You should try this one
http://sourceforge.net/projects/libbigint/

great library for things like this.

also you can use boost.

http://www.boost.org/doc/libs/1_53_0/libs/multiprecision/doc/html/boost_multiprecision/intro.html

also one of the most commons is
https://gmplib.org/

score 0 · Answer 5 · answered Apr 23 '15 at 00:23

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Depends on the usage.If you need to do computation on it, probably go with the Big Int Library. If not and only aim is storing, store it in an array with each digit stored in one array element.

answered Apr 23 '15 at 00:23

chappa

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How to store a very large number in c++

5 Answers5