(C++) StrToDouble

 

StrToDouble is a code snippet to convert a std::string to double. DoubleToStr converts an double to std::string.

 

StrToDouble has multiple versions:

• StrToDouble using the C++98 and the STL
• StrToDouble using the C++98 and the Boost library
• StrToDouble using the C++11 and the STL

 

 

 

 

 

StrToDouble using the C++98 and the STL

 

Uses std::atof.

 

---

#include <string> //From http://www.richelbilderbeek.nl/CppStrToDouble.htm const double StrToDouble(const std::string& s) {   return std::atof(s.c_str()); }

 

 

 

 

 

StrToDouble using the C++98 and the Boost library

 

Uses boost::lexical_cast.

 

---

#include <string> #include <boost/lexical_cast.hpp> const double StrToDouble(const std::string& s) {   return boost::lexical_cast<double>(s); }

 

 

 

 

 

StrToDouble using the C++11 and the STL

 

Uses std::stod.

 

---

#include <string> //From http://www.richelbilderbeek.nl/CppStrToDouble.htm double StrToDouble(const std::string& s) {   return std::stod(s); }

 

 

 

 

 

StrToDouble testing code

 

• Download the Qt Creator project 'CppStrToDouble' (zip)

 

---

#include <string> //From http://www.richelbilderbeek.nl/CppStrToDouble.htm double StrToDoubleStl(const std::string& s) {   return std::atof(s.c_str()); } //From http://www.richelbilderbeek.nl/CppStrToDouble.htm double StrToDoubleCpp0x(const std::string& s) {   return std::stof(s); } #include <boost/lexical_cast.hpp> //From http://www.richelbilderbeek.nl/CppStrToDouble.htm double StrToDoubleBoost(const std::string& s) {   return boost::lexical_cast<double>(s); } bool CanStrToDoubleStl(const std::string& s) {   const double i = std::atof(s.c_str());   return i!=0.0 || s=="0.0"; } double CanStrToDoubleCpp0x(const std::string& s) {   try { std::stof(s); }   catch (std::exception&) { return false; }   return true; } double CanStrToDoubleBoost(const std::string& s) {   try { boost::lexical_cast<double>(s); }   catch (boost::bad_lexical_cast&) { return false; }   return true; } #include <cassert> ///fuzzy_equal_to is a predicate to test two doubles for equality ///with a certain tolerance. A tolerance of 0.0 denotes that ///an exact match is requested. Note that the value of 0.0 cannot ///be compared fuzzily. //From http://www.richelbilderbeek.nl/CppFuzzy_equal_to.htm struct fuzzy_equal_to   : public std::binary_function<double,double,bool> {   fuzzy_equal_to(const double tolerance = 0.01)     : m_tolerance(tolerance)   {     assert(tolerance >= 0.0);   }   bool operator()(const double lhs, const double rhs) const   {     return rhs > (1.0 - m_tolerance) * lhs         && rhs < (1.0 + m_tolerance) * lhs;   }   const double m_tolerance; }; int main() {   assert(!CanStrToDoubleStl("a"));   assert(!CanStrToDoubleCpp0x("a"));   assert(!CanStrToDoubleBoost("a"));   assert(CanStrToDoubleStl("0.0"));   assert(CanStrToDoubleCpp0x("0.0"));   assert(CanStrToDoubleBoost("0.0"));   assert(CanStrToDoubleStl("123.456"));   assert(CanStrToDoubleCpp0x("123.456"));   assert(CanStrToDoubleBoost("123.456"));   const std::string s = "123.456";   assert(fuzzy_equal_to(0.00001)(StrToDoubleStl(s),StrToDoubleCpp0x(s)));   assert(fuzzy_equal_to(0.00001)(StrToDoubleStl(s),StrToDoubleBoost(s))); }