Rounding off floats with ostringstream

Question

I have an issue regarding conversion from float to c++ string using ostringstream. Here is my line:

void doSomething(float t)
{
    ostringstream stream; 
    stream << t;
    cout << stream.str();
}

when t has value -0.89999 it is round off to -0.9, but when it's value is 0.0999 or lesser than this say 1.754e-7, it just prints without round off. what can be the solution for this.

Solution 1

You need to set the precision for ostringstream using precision

e.g

stream.precision(3);
stream<<fixed;    // for fixed point notation
//cout.precision(3); // display only
stream << t;

cout<<stream.str();

Solution 2

If you want a particular number of significant figures displayed try using setprecision(n) where n is the number of significant figures you want.

#include <iomanip>

void doSomething(float t)
{
    ostringstream stream; 
    stream << std::setprecision(4)  << t;
    cout <<  stream.str();
}

Solution 3

If you want fixed-point instead of scientific notation, use std::fixed:

stream << std::fixed << t;

Additionally you might want to set the precision as mentioned.

Comments

[boom]

i got solution for 0.0999, but for the number of 7.9e-08 i am still getting the same. so what can be the solution for this.

[boom]

i got solution for 0.0999, but for the number of 7.9e-08 i am still getting the same. so what can be the solution for this.

[yadab]

you need to set precision to the stream itself. i.e. stream.precision(3);

[boom]

i am doing the same. here is my code:ostringstream stream; stream.precision(1); stream << t; cout << endl<<"Value:"<< stream.str();

[yadab]

okay, use a fixed precision. e.g, stream.precision(8); stream << fixed; stream << t; cout << endl<<"Value:"<< stream.str();

[stephanmg]

What is the default precision for ostringstream?