CanCast is a checking code snippet that let you check if you can convert a std::string to another data type when using LexicalCast.

CanCast serves the same purpose as CanLexicalCast, but does not throw an exception and does not use Boost. Note that there are differences between CanCast and CanLexicalCast, as CanLexicalCast is more strict. Below the code, a comparison between the two is shown.


#include <string>

#include <sstream>



//From http://www.richelbilderbeek.nl/CppCanCast.htm

template <class TargetType> const bool CanCast(const std::string& from)

{

  std::istringstream i(from);

  TargetType temp;

  return ( (i >> temp) ? true : false );

}

Comparison between CanCast and CanLexicalCast

The table below shows if a std::string can be converted according to CanCast (CC) and CanLexicalCast (CLC). Note that the first std::string was a space (' '). Below the table I show the code I've used to generate this output. CanCast serves the same purpose as CanLexicalCast, but does not throw an exception and does not use Boost. Note that there are differences between CanCast and CanLexicalCast, as CanLexicalCast is more strict.

Type	int	int	double	double
string	CC	CLC	CC	CLC
	false	false	false	false
a	false	false	false	false
1	true	true	true	true
1,1	true	false	true	false
1.1	true	false	true	true
1.1.1	true	false	true	false
-1	true	true	true	true
-1.1	true	false	true	true
-1.1.1	true	false	true	false


#include <vector>

 

int main()

{

  std::vector<std::string> v;

  v.push_back("");

  v.push_back("a");

  v.push_back("1");

  v.push_back("1,1");

  v.push_back("1.1");

  v.push_back("1.1.1");

  v.push_back("-1");

  v.push_back("-1.1");

  v.push_back("-1.1.1");

 

    std::cout << "Type"

      << '\t' << "int"

      << '\t' << "int"

      << '\t' << "double"

      << '\t' << "double"

      << std::endl;

    std::cout << "string"

      << '\t' << "CC"

      << '\t' << "CLC"

      << '\t' << "CC"

      << '\t' << "CLC"

      << std::endl;

 

  std::cout << std::boolalpha;

 

  const std::size_t size = v.size();

  for (std::size_t i=0; i!=size; ++i)

  {

    std::cout << v[i]

      << '\t' << CanCast<int>(v[i])

      << '\t' << CanLexicalCast<int>(v[i])

      << '\t' << CanCast<double>(v[i])

      << '\t' << CanLexicalCast<double>(v[i])

      << '\n';

  }

}

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(C++) CanCast

Comparison between CanCast and CanLexicalCast