Double data type rounding off to float accuracy for no apparent reason [duplicate]

This question already has an answer here:

• How do I print a double value with full precision using cout? 10 answers

The following code:

#include<iostream.h>
void main(){
    double d = 1.234567;
    cout<<d;
}

The output is: 1.23457

What could possibly be the reason for this? Keep in mind that I'm using a 25 year old(Borland 4.5) compiler, because that is what my course required me to use.