Boost::lexical_cast和非内置类型的字符串化
boost::lexical_cast and stringification of non-builtin types
我有一个(可能)简单的问题关于boost::lexical_cast与复合类型(在我的情况下std::vector
.
我的第一个模板化的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();
}
,下面是一个工作示例:
vector<int> x(10,-3;
cout << stringify<vector<int> >(x) << endl;
显示输出"-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
如果为vector
创建一个专门的模板,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;
}
任何建议吗?
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
您可能已经在全局名称空间中为向量声明了operator<<
,而boost::lexical_cast
将只查看boost::
名称空间和std::
名称空间,其中定义了ostream
。通过在namespace std { ... }
中包装operator<<
的声明和定义,尝试将您的重载添加到std::
命名空间。
我可能在这里的方式,但我个人认为你会更好,而不是试图字符串化一个容器,你做一个'序列化'的方法为所有的容器。
固定编辑:
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:也就是说,如果你想在stringify中使用向量,那么你可以这样做。
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,但这就是要点。
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