(C++) Compile-time Strategy Design Pattern example: StrToDouble

 

Compile-time Strategy Design Pattern example: StrToDouble is a compile-time Strategy Design Pattern.

 

You can also employ a run-time Strategy Design Pattern.

 

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

 

 

 

 

 

 

 

 

Technical facts

 

Application type(s)

• Desktop application

Operating system(s) or programming environment(s)

• Lubuntu 12.10 (quantal)

IDE(s):

• Qt Creator 2.5.2

Project type:

• Console application

C++ standard:

• C++11

Compiler(s):

• G++ 4.7.2

Libraries used:

• STL: GNU ISO C++ Library, version 4.7.2

 

 

 

 

 

Qt project file: CppCtStrategyDesignPatternExampleStrToDouble.pro

 

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TEMPLATE = app CONFIG += console CONFIG -= qt QMAKE_CXXFLAGS += -std=c++11 -Wall -Wextra -Weffc++ SOURCES += main.cpp

 

 

 

 

 

main.cpp

 

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#include <boost/lexical_cast.hpp> #include <string> ///A compile-time Strategy Design Pattern enum CtStrategyPolicy { Use_stl, Use_boost, Use_cpp11 }; template <CtStrategyPolicy> struct CtStrategy {   static double StrToDouble(const std::string& s); }; template<> double CtStrategy<Use_stl>::StrToDouble(const std::string& s) {   return std::atof(s.c_str()); } template<> double CtStrategy<Use_boost>::StrToDouble(const std::string& s) {   return boost::lexical_cast<double>(s); } template<> double CtStrategy<Use_cpp11>::StrToDouble(const std::string& s) {   return std::stof(s); } #include <cassert> int main() {   const CtStrategy<Use_stl> a;   const CtStrategy<Use_boost> b;   const CtStrategy<Use_cpp11> c;   assert( std::abs(12.34 - a.StrToDouble("12.34")) < 0.000001);   assert( std::abs(12.34 - b.StrToDouble("12.34")) < 0.000001);   assert( std::abs(12.34 - c.StrToDouble("12.34")) < 0.000001); }