In this article we will discuss different ways to convert double to String or char array with or without precision i.e.
double to String using C++11’s std::to_string
std::to_string is introduced in c++11.
Example to convert double to std::string using to_string is as follows,
double num = 6789898989.33999443; //Converting using std::to_string std::string str = std::to_string(num);
Output:
6789898989.339994
It has default precision of 6 digits and we cannot change it. If you want customised precision then you should use stringstream.
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double to String using ostringstream
Header file Required
#include <sstream>
Example to convert double to std::string using ostringstream is as follows,
// Create an output string stream std::ostringstream streamObj; //Add double to stream streamObj << num; // Get string from output string stream std::string strObj = streamObj.str();
Output
6.7899e+09
For Big Numbers ostringstream will automatically convert it to scientific notation.
double to String with scientific notation using ostringstream
Add std::fixed to stream i.e.
// Set Fixed -Point Notation streamObj2 << std::fixed;
It will force the ostringstream to convert double using fixed-point notation instead of scientific one. For example,
// Create an output string stream std::ostringstream streamObj2; // Set Fixed -Point Notation streamObj2 << std::fixed; //Add double to stream streamObj2 << num; // Get string from output string stream std::string strObj2 = streamObj2.str();
Output
6789898989.339994
By default, precision is up to max 6 in stringstream’s double to string conversion.
double to String with Custom Precision using ostringstream
Header file Required
#include <iomanip>
To convert Double to String with Custom Precision set precision in stringstream i.e.
Let’s set precision to 2 i.e.
// Set precision to 2 digits streamObj << std::setprecision(2);
Check this,
// Create an output string stream std::ostringstream streamObj3; // Set Fixed -Point Notation streamObj3 << std::fixed; // Set precision to 2 digits streamObj3 << std::setprecision(2); //Add double to stream streamObj3 << num; // Get string from output string stream std::string strObj3 = streamObj3.str();
Output:
6789898989.34
double to String / Char array using C’s snprintf
char buffer[32]; memset(buffer, 0, sizeof(buffer)); snprintf(buffer, sizeof(buffer), "%g", num); std::string strObj4(buffer);
Output
6.7899e+09
double to String boost’s lexical_cast
Header file Required
#include <boost/lexical_cast.hpp>
Example,
std::string strObj5 = "0.0";
try
{
strObj5 = boost::lexical_cast<std::string>(num);
}
catch (boost::bad_lexical_cast const& e)
{
std::cout << "Error: " << e.what() << "\n";
}
Output
6789898989.3399944
Complete example is as follows,
#include <string>
#include <iostream>
#include <sstream>
#include <boost/lexical_cast.hpp>
#include <iomanip>
int main()
{
double num = 6789898989.33999443;
std::cout << "Converting using std::to_string" << std::endl;
std::string str = std::to_string(num);
std::cout << str << std::endl;
/****************************************/
std::cout << "Converting double to string using ostringstream" << std::endl;
// Create an output string stream
std::ostringstream streamObj;
//Add double to stream
streamObj << num;
// Get string from output string stream
std::string strObj = streamObj.str();
std::cout << strObj << std::endl;
/****************************************/
std::cout<< "Converting double to string without scientific Notation using ostringstream" << std::endl;
// Create an output string stream
std::ostringstream streamObj2;
// Set Fixed -Point Notation
streamObj2 << std::fixed;
//Add double to stream
streamObj2 << num;
// Get string from output string stream
std::string strObj2 = streamObj2.str();
std::cout << strObj2 << std::endl;
/****************************************/
std::cout<< "Converting double to string with custom precision 2"<< std::endl;
// Create an output string stream
std::ostringstream streamObj3;
// Set Fixed -Point Notation
streamObj3 << std::fixed;
// Set precision to 2 digits
streamObj3 << std::setprecision(2);
//Add double to stream
streamObj3 << num;
// Get string from output string stream
std::string strObj3 = streamObj3.str();
std::cout << strObj3 << std::endl;
/****************************************/
std::cout << "Converting double to string with snprintf" << std::endl;
char buffer[32];
memset(buffer, 0, sizeof(buffer));
snprintf(buffer, sizeof(buffer), "%g", num);
std::string strObj4(buffer);
std::cout << strObj4 << std::endl;
/****************************************/
std::cout << "Converting double to string with Boost's lexical_cast"<< std::endl;
std::string strObj5 = "0.0";
try
{
strObj5 = boost::lexical_cast<std::string>(num);
}
catch (boost::bad_lexical_cast const& e)
{
std::cout << "Error: " << e.what() << "\n";
}
std::cout << strObj5 << std::endl;
}
Output:
Converting using std::to_string 6789898989.339994 Converting double to string using ostringstream 6.7899e+09 Converting double to string without scientific Notation using ostringstream 6789898989.339994 Converting double to string with custom precision 2 6789898989.34 Converting double to string with snprintf 6.7899e+09 Converting double to string with Boost's lexical_cast 6789898989.3399944