I' d like to use lexical_cast to convert a float to a string. Usually it works fine, but I have some problems with numbers without decimal. How can I fix number of decimal shown in the string?
Example:
double n=5;
string number;
number = boost::lexical_cast<string>(n);
Result number is 5, I need number 5.00.
From the documentation for boost lexical_cast:
For more involved conversions, such as where precision or formatting need tighter control than is offered by the default behavior of lexical_cast, the conventional stringstream approach is recommended. Where the conversions are numeric to numeric, numeric_cast may offer more reasonable behavior than lexical_cast.
Example:
#include <sstream>
#include <iomanip>
int main() {
std::ostringstream ss;
double x = 5;
ss << std::fixed << std::setprecision(2);
ss << x;
std::string s = ss.str();
return 0;
}
If you need complex formatting, use std::ostringstream instead. boost::lexical_cast is meant for "simple formatting".
std::string
get_formatted_value(double d) {
std::ostringstream oss;
oss.setprecision(3);
oss.setf(std::ostringstream::showpoint);
oss << d;
return oss.str();
}
you can also use sprintf, which is faster then ostringstream
#include <cstdio>
#include <string>
using namespace std;
int main()
{
double n = 5.0;
char str_tmp[50];
sprintf(str_tmp, "%.2f", n);
string number(str_tmp);
}