Question

对于带有复合类型的boost :: lexical_cast，我有一个（也许）简单的问题（在我的情况下是std::vector。

我的第一个模板化字符串化函数版本如下

template <typename T>
std::string stringiy(const T &t)
{
std::ostringstream o;
o<< t;
return o.str();
}

以下是一个工作实例：

vector<int> x(10,-3;
cout << stringify<vector<int> >(x) << endl;

输出 "-3-3-3-3-3-3-3-3"~ 但出于性能原因，我想利用boost::lexical_cast

现在我改变了函数实现：

template <typename T>
std::string stringiy(const T &t)
{
   return boost::lexical_cast<string>(t);
}

虽然此方法适用于内置类型，但当它用于std::vector

时，它会停止处理上一个类似的情况

如果为向量创建专用模板

，问题仍然存在（它不会编译）

template <typename T>
std::string stringiy(const std::vector<T> &t)
{
     vector<string> strret = num2str(t);
     string r;
     for ( vector<string>::iterator iter = strret.begin(); iter!=strret.end(); ++iter )
    r.append(*iter);
     return r;
}

有什么建议吗？

g ++ - 4.5，ubuntu 11.10 amd64

In file included from Util.h:41:0,
                 from testLexicalCast.cpp:49:
/usr/include/boost/lexical_cast.hpp: In member function ‘bool boost::detail::lexical_stream<Target, Source, Traits>::operator<<(const Source&) [with Target = std::basic_string<char>, Source = std::vector<double>, Traits = std::char_traits<char>]’:
/usr/include/boost/lexical_cast.hpp:1151:13:   instantiated from ‘Target boost::detail::lexical_cast(typename boost::call_traits<Source>::param_type, CharT*, size_t) [with Target = std::basic_string<char>, Source = std::vector<double>, bool Unlimited = true, CharT = char, typename boost::call_traits<Source>::param_type = const std::vector<double>&, size_t = long unsigned int]’
/usr/include/boost/lexical_cast.hpp:1174:77:   instantiated from ‘Target boost::lexical_cast(const Source&) [with Target = std::basic_string<char>, Source = std::vector<double>]’
Util.h:211:43:   instantiated from ‘std::string util::stringify(const T&) [with T = std::vector<double>, std::string = std::basic_string<char>]’
testLexicalCast.cpp:72:53:   instantiated from here
/usr/include/boost/lexical_cast.hpp:595:48: error: no match for ‘operator<<’ in ‘((boost::detail::lexical_stream<std::basic_string<char>, std::vector<double>, std::char_traits<char> >*)this)->boost::detail::lexical_stream<std::basic_string<char>, std::vector<double>, std::char_traits<char> >::stream << input’
/usr/include/c++/4.5/ostream:108:7: note: candidates are: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:117:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>, std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]
/usr/include/c++/4.5/ostream:127:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:165:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:169:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:173:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/bits/ostream.tcc:91:5: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.5/ostream:180:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/bits/ostream.tcc:105:5: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.5/ostream:191:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:200:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:204:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:209:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:213:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:221:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:225:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/bits/ostream.tcc:119:5: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]
make: *** [testLexicalCast.o] Error 1

Answer 1

您可能已在全局命名空间中声明了operator<<个向量，而boost::lexical_cast只会在boost::命名空间和std::命名空间中查找ostream std:: 1}}已定义。通过在operator<<中包装namespace std { ... }的声明和定义，尝试将重载添加到{{1}}命名空间。

Answer 2

我可能会离开这里，但我个人认为你会更好，而不是尝试对你为所有容器制作'序列化'方法的容器进行字符串化。

编辑：修复

template<typename Container>
   std::string serialize_container(const Container& container)
{
     std::stringstream ss;
     std::copy(container.begin(), container.end(),    
              std::ostream_iterator<typename Container::value_type>(ss,"-"));
     return ss.str();    
}

编辑：如果你想使用带字符串化的矢量，那你就这样做了。

template <typename T, typename A=void>
std::string stringiy(const T& t)
{
    //...
} 

template <typename T, typename A>
std::string stringiy(const std::vector<T, A>& container)
{
     std::stringstream ss;

     //if << is overloaded for vector
     ss << container;

     /*//else
     std::copy(container.begin(), container.end(),
               std::ostream_iterator<T>(ss,"-"));    
     //        std::ostream_iterator<typename Container::value_type>(ss,"-"));
     */
     return ss.str();    
}

N.B未经测试，但这是要点。

boost :: lexical_cast和非内置类型的字符串化

2 个答案: