using stringstream to print a rounded floating point number

c++ string stringstream
drjrm3 picture drjrm3 · Oct 12, 2011 · Viewed 8k times · Source

i have floating point variables "lmin" and "lmax". i wish to display only 4 significant digits. i am currently using something i have found online of the form ...

string textout;
stringstream ss;

ss << lmin;
textout = ss.str();
output(-0.5, -0.875, textout);

ss.str("");
ss << lmax;
textout = ss.str();
output(0.2, -0.875, textout);

where "output" is simply a function i wrote to parse the string and print it to the screen. the important point, is how do i print only a ROUNDED version of lmin and lmax to ss?

Answer

Praetorian picture Praetorian · Oct 12, 2011

Use std::setprecision to specify the number of digits after the decimal point.

#include <sstream>
#include <iostream>
#include <iomanip>

int main()
{
  double d = 12.3456789;
  std::stringstream ss;

  ss << std::fixed << std::setprecision( 4 ) << d;

  std::cout << ss.str() << std::endl;
}

Output:

12.3457

Related questions

stringstream, string, and char* conversion confusion

My question can be boiled down to, where does the string returned from stringstream.str().c_str() live in memory, and why can't it be assigned to a const char*? This code example will explain it better than I can #…

Read More
How do I convert from stringstream to string in C++?

How do I convert from std::stringstream to std::string in C++? Do I need to call a method on the string stream?

Read More
How do I check if a C++ string is an int?

When I use getline, I would input a bunch of strings or numbers, but I only want the while loop to output the "word" if it is not a number. So is there any way to check if "word" is …

Read More