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Synopsis

lexical_cast
bad_lexical_cast

Library features defined in boost/lexical_cast.hpp:

namespace boost
{
    class bad_lexical_cast;

    template<typename Target, typename Source>
      Target lexical_cast(const Source& arg);

    template <typename Target>
      Target lexical_cast(const AnyCharacterType* chars, std::size_t count);
}

template<typename Target, typename Source>
  Target lexical_cast(const Source& arg);

Returns the result of streaming arg into a standard library string-based stream and then out as a Target object. Where Target is either std::string or std::wstring, stream extraction takes the whole content of the string, including spaces, rather than relying on the default operator>> behavior. If the conversion is unsuccessful, a bad_lexical_cast exception is thrown.

template <typename Target>
  Target lexical_cast(const AnyCharacterType* chars, std::size_t count);

Takes an array of count characters as input parameter and streams them out as a Target object. If the conversion is unsuccessful, a bad_lexical_cast exception is thrown. This call may be useful for processing nonzero terminated array of characters or processing just some part of character array.

The requirements on the argument and result types for both functions are:

  • Source is OutputStreamable, meaning that an operator<< is defined that takes a std::ostream or std::wostream object on the left hand side and an instance of the argument type on the right.
  • Target is InputStreamable, meaning that an operator>> is defined that takes a std::istream or std::wistream object on the left hand side and an instance of the result type on the right.
  • Target is CopyConstructible [20.1.3].
  • Target is DefaultConstructible, meaning that it is possible to default-initialize an object of that type [8.5, 20.1.4].

The character type of the underlying stream is assumed to be char unless either the Source or the Target requires wide-character streaming, in which case the underlying stream uses wchar_t. Following types also can use char16_t or char32_t for wide-character streaming:

  • Single character: char16_t, char32_t
  • Arrays of characters: char16_t *, char32_t *, const char16_t *, const char32_t *
  • Strings: std::basic_string, boost::containers::basic_string
  • boost::iterator_range<WideCharPtr>, where WideCharPtr is a pointer to wide-character or pointer to const wide-character
  • boost::array<CharT, N> and std::array<CharT, N>, boost::array<const CharT, N> and std::array<const CharT, N>
[Important] Important

Many compilers and runtime libraries fail to make conversions using new Unicode characters. Make sure that the following code compiles and outputs nonzero values, before using new types:

std::cout
    << boost::lexical_cast<std::u32string>(1.0).size()
    << "  "
    << boost::lexical_cast<std::u16string>(1.0).size();

Where a higher degree of control is required over conversions, std::stringstream and std::wstringstream offer a more appropriate path. Where non-stream-based conversions are required, lexical_cast is the wrong tool for the job and is not special-cased for such scenarios.

class bad_lexical_cast : public std::bad_cast
{
public:
    ... // same member function interface as std::exception
};

Exception used to indicate runtime lexical_cast failure.


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