Can I print -0.000 as 0.000?

Question

printf("%.3lf\n", -0.0001);

This outputs -0.000, but shouldn't it be 0.000?

How can I make this print without the minus sign, i.e. 0.000 ?

Answer 1

The correct answer has already been given. Just wanted to add that you'll get the same from c++ cout

If you want to get rid of the sign, it can be done like this:

double fixSign(double d)
{
    std::ostringstream strs;
    strs << std::fixed << std::setprecision(3) << d;
    std::string str = strs.str();

    if (str == "-0.000") return 0.0;

    return d;
}

int main()
{
    double d=-0.0001;

    printf("%.3lf\n", d);

    cout << std::fixed << std::setprecision(3) << d << endl;

    cout << std::fixed << std::setprecision(3) << fixSign(d) << endl;

    return 0;
}

output:

-0.000
-0.000
0.000

EDIT Could this be done without converting to string?

How about:

#define PRE 3
#define LIMIT -0.0005  // Must have PRE zeros after the decimal point

// VERSION WITHOUT USE OF STRING
double fixSign_v2(double d)
{
    if ((d < 0) && (d > LIMIT)) return 0;

    return d;
}

double fixSign(double d)
{
    std::ostringstream strs;
    strs << std::fixed << std::setprecision(PRE) << d;
    std::string str = strs.str();

    if (str == "-0.000") return 0.0;

    return d;
}

int main()
{
    // PRE == 2
    //double d1=-0.005;
    //double d2=-0.0049999999999;

    // PRE == 3
    double d1=-0.0005;
    double d2=-0.000499999999999;

    // PRE == 10
    //double d1=-0.00000000005;
    //double d2=-0.0000000000499999999;

    cout << std::fixed << std::setprecision(PRE+20) << d1 << endl;

    cout << std::fixed << std::setprecision(PRE) << fixSign(d1) << endl;

    cout << std::fixed << std::setprecision(PRE) << fixSign_v2(d1) << endl;

    cout << "------------------------" << endl;

    cout << std::fixed << std::setprecision(PRE) << d2 << endl;

    cout << std::fixed << std::setprecision(PRE) << fixSign(d2) << endl;

    cout << std::fixed << std::setprecision(PRE) << fixSign_v2(d2) << endl;

    return 0;
}

output:

-0.001
-0.001
-0.001
------------------------
-0.000
0.000
0.000

so it seems to work!

But it won't work for all rounding modes.

Therefore it seems safer to use the first version with string convert.