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GCC option for printing large number (large double)

+1 vote

I have an issue in printing a large number in a c program. Please find below the code snippet :

int main()
 double temp = 0.0;
 temp = pow(2, 2000);
 printf("The value of temp is %lfn", temp);
 return 0;

I compiled and ran as below:

$ gcc test.c -o test
$ ./test
The value of temp is inf

But for the same expression, I am able to get the value from python,

$ python
>>> pow(2,2000)

Can any body help me with that option?

posted Sep 13, 2013 by Bob Wise

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2 Answers

+1 vote

There is no GCC option that will help you here. Python and C are two different languages and they represent numbers in different ways. To do this kind of thing in C you will need to use some sort of bignum library, such as libmpfr.

answer Sep 13, 2013 by Kumar Mitrasen
+1 vote

I would suggest you have a look at the Gnu MP library, which deals with big integers, floats and gives you lots of things that you can normally find in languages like Python, Go or Java.

An example would be:

 mpz_t a;
 mpz_set_str(a, "10000000000000000000000000000", 10);
 gmp_printf("%Zd", a);

which will print this number back to you, and %Zx will print the Hex version of it.

answer Sep 13, 2013 by Garima Jain
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I don't really understand this option. I enabled it but it warns for essentially all of my classes which have any virtual methods. For
example if I have Foo.h:

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then Foo.cpp which implements Foo. And then in another header somewhere else I inherit from Foo and implement bar() differently (as a virtual function). However when GCC compiles Foo.cpp it can't see the other header, so I guess it assumes no one inherits from Foo and suggests it should be marked final:

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I mean sure, it would, but that would defeat the entire point (as I understand it).

I don't really understand how/where this option is meant to be used.
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