c++ - Precision error in double -


a large double value gets changed when printed %lf values upto following combination gives proper results 9 digits before decimal / 6 digits after decimal e.g. of value 9 digits before decimal printed %lf input : 3435537287.32 output : 3435537287.320000

once increase digits before decimal 10, values printed %lf adds garbage value. e.g. of value 10 digits before decimal printed %lf input : 34355372871.3487 output : 34355372871.348701 can see above output input value changed.

is there compile time option g++/xlc++ can used value is'nt changed?

::code snippet:: 

double d2 =  34355372871.3487;  double d4 =  3435537287.3487;   printf("d2 = %lf\n", d2);  printf("d4 = %lf\n", d4);

thanks, hudson

it precision of double. double stored 64 bits (8bytes).

(http://en.wikipedia.org/wiki/double-precision_floating-point_format)

it uses 52 bits mantissa, 1 bit signal , 11 bits exponent.

then, 52 bits mantissa gives 15–17 significant decimal digits precision.


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