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Difference between revisions of "Talk:cpp/string/basic string/to string"

From cppreference.com
(Created page with "==== Not round-trip safe. ==== Please mention that {{lc|std::to_string}} is not round-trip-safe for floating point numbers. Please mention "not round-trip-safe" explaining th...")
 
Line 22: Line 22:
 
     const std::string sNum    = oss.str();
 
     const std::string sNum    = oss.str();
 
     const std::string sNumBad = std::to_string(x);
 
     const std::string sNumBad = std::to_string(x);
−
     std::cout << "sNum    == " << sNum << " (round-trip-safe!)\n";
+
     std::cout << "sNum    == " << sNum << " (round-trip-safe!)\n";
−
     std::cout << "sNumBad == " << sNum << '\n';
+
     std::cout << "sNumBad == " << << '\n';
  
 
     double y;
 
     double y;

Revision as of 09:45, 26 July 2023

Not round-trip safe.

Please mention that std::to_string is not round-trip-safe for floating point numbers. Please mention "not round-trip-safe" explaining that converting a double to a std::string and then back to a double will not yield the same number in every case.

Please provide an example of how to perform a round-trip-safe conversion, e.g. maybe something similar to this:

Run this code
#include <iostream>
#include <iomanip>
#include <string>
#include <limits>
#include <sstream>
#include <cassert>
 
int main()
{
    double x = 3.33333333333333333333333333;
 
    std::ostringstream oss;
    oss << std::setprecision(std::numeric_limits<decltype(x)>::max_digits10) << x;
    const std::string sNum    = oss.str();
    const std::string sNumBad = std::to_string(x);
    std::cout << "sNum    == " << sNum    << " (round-trip-safe!)\n";
    std::cout << "sNumBad == " << sNumBad << '\n';
 
    double y;
    double yBad;
 
    std::istringstream(sNum)    >> y;
    std::istringstream(sNumBad) >> yBad;
    std::cout << "(x == y   ) is " << std::boolalpha << (x==y)    << '\n';
    std::cout << "(x == yBad) is " << std::boolalpha << (x==yBad) << '\n';
}
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